Arctic winter warms up to a low summer ice season

Sea ice extent in the Bering Sea remains at record low levels for this time of year. Total ice extent over the Arctic Ocean also remains low.

Overview of conditions

Figure 1. Arctic sea ice extent for March 2018 was 14.30 million square kilometers (5.52 million square miles). The magenta line shows the 1981 to 2010 average extent for the month.

Figure 1. Arctic sea ice extent for April 2018 was 13.71 million square kilometers (5.29 million square miles). The magenta line shows the 1981 to 2010 average extent for the month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent for April 2018 averaged 13.71 million square kilometers (5.29 million square miles). This was 980,000 square kilometers (378,400 square miles) below the 1981 to 2010 average and only 20,000 square kilometers (7,700 square miles) above the record low April extent set in 2016. Given the uncertainty in measurements, NSIDC considers 2016 and 2018 as tying for lowest April sea ice extent on record. As seen throughout the 2017 to 2018 winter, extent remained below average in the Bering Sea and Barents Sea. While retreat was especially pronounced in the Sea of Okhotsk during the month of April, the ice edge was only slightly further north than is typical at this time of year. Sea ice extent in the Bering Sea remains the lowest recorded since at least 1979. The lack of sea ice within this region created many coastal hazards this past winter.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of April 4, 2018, along with daily ice extent data for four previous years and 2012, the year with record low minimum extent. 2018 is shown in blue, 2017 in green, 2016 in orange, 2015 in brown, 2014 in purple, and 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data.

Figure 2. The graph above shows Arctic sea ice extent as of April 30, 2018, along with daily ice extent data for four previous years and 2012, the year with record low minimum extent. 2018 is shown in blue, 2017 in green, 2016 in orange, 2015 in brown, 2014 in purple, and 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Overall, sea ice extent for April 2018 declined by 920,000 square kilometers (355,000 square miles). The amount of ice lost for the month was less than the 1981 to 2010 average of 1.1 million square kilometers (424,700 square miles). The ice edge retreated everywhere except in Hudson Bay and Baffin Bay/Davis Strait. The sea ice expanded slightly within Davis Strait during the month. Sea ice in the Hudson Bay usually does not begin to retreat until the end of May.

Air temperatures at 925 hPa (about 2,500 feet above sea level) for April were up to 10 degrees Celsius (18 degrees Fahrenheit) higher than average in the East Siberian Sea and stretching towards the pole. Air temperatures were also up to 5 degrees Celsius (9 degrees Fahrenheit) above average within the East Greenland Sea and 3 degrees Celsius (5 degrees Fahrenheit) above average over Baffin Bay. By contrast, air temperatures were near average within the Barents and Kara seas and lower than average over Canada and the Hudson Bay. The pattern of temperature departures from average resulted from higher than average sea level pressure over the Beaufort Sea as well as the North Atlantic, combined with below average sea level pressure over Eurasia and western Greenland through eastern Canada. On the Pacific side of the Arctic, this pressure pattern drove warm air from the south over the East Siberian and Chukchi Seas, while bringing cold air into northern Canada. The pattern of above average sea level pressure over the North Atlantic was combined with lower than average sea level pressure over western Greenland and the Canadian Archipelago, bringing in warm air in from the south over Greenland and Baffin Bay.

April 2018 compared to previous years

Figure 3. Monthly March ice extent for 1979 to 2018 shows a decline of 2.7 percent per decade.

Figure 3. Monthly April ice extent for 1979 to 2018 shows a decline of 2.6 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

The linear rate of decline for April sea ice extent is 37,500 square kilometers (14,500 square miles) per year, or 2.6 percent per decade relative to the 1981 to 2010 average.

Continued loss of the oldest sea ice, five-years or older

Figure 4a-d. These maps show the ice age distribution during week 9 in 1984 (a) and 2018 (b). The time-series (c) shows total sea ice extent for different age classes as is outlined in the Arctic Ocean Domain (d). Credit: Preliminary analysis courtesy M. Tschudi, University of Colorado Boulder. Images by M. Tschudi, S. Stewart, University of Colorado, Boulder, and W. Meier, J. Stroeve, NSIDC|

Figure 4a-d. These maps show the ice age distribution during week nine in 1984 (a) and 2018 (b). The time-series (c) shows total sea ice extent for different age classes as is outlined in the Arctic Ocean Domain (d).

Credit: Preliminary analysis courtesy M. Tschudi, University of Colorado Boulder. Images by M. Tschudi, S. Stewart, University of Colorado, Boulder, and W. Meier, J. Stroeve, NSIDC
High-resolution image

An updated assessment of ice age changes in the Arctic through week nine (early March) in 2018 shows a substantial amount of first-year ice within the Beaufort, Chukchi, East Siberian, Laptev, Kara and Barents Seas (Figure 4b). Multiyear ice near the Alaskan and Siberian coast is limited to scattered regions off shore in the Beaufort and Chukchi Seas. A tongue of second- and third-year ice extends from near the pole toward the New Siberian Islands, and a region of second-year ice extends toward Severnaya Zemlya. As averaged over the Arctic Ocean domain (Figure 4d), the multiyear ice cover has declined from 61 percent in 1984 to 34 percent in 2018. In addition, only 2 percent of the ice age cover is categorized as five-plus years, the least amount recorded during the winter period. While the proportion of first-year versus multiyear ice will largely depend on how much ice melted during summer, how much ice is exported out of Fram Strait each winter also plays a role. First-year ice grows to about 1.5 to 2 meters (5 to 6.5 feet) thick over a winter season, while older ice is often 3 to 4 meters (9.8 to 13.1 feet) thick.

Note: The ice age fields originally posted on Thursday, May 3, were incorrect. The ice age field has its “birthday” each September after the minimum, when all of the age values are incremented by one after the end of the summer melt season. For example, first-year ice becomes second-year ice after the minimum, second-year ice becomes third-year ice, and so on. However, in the original post, the near-real-time age fields were not incremented after the 2017 minimum. The ice age fields are now corrected (as of Monday, May 7). However, as these are near-real-time data, minor adjustments may occur during final processing. Final numbers will be available in the next few months.

Is winter warming resulting in less winter ice growth?

Figure 5a. These maps show the cumulative number of freezing degree day anomalies from the Climate Forecast System version 2 (CFSv2). Courtesy of A. Barrett, National Snow and Ice Data Center|

Figure 5a. These maps show the cumulative number of freezing degree day anomalies from the Climate Forecast System version 2 (CFSv2).

Credit: A. Barrett, National Snow and Ice Data Center
High-resolution image

Figure xx. This time-series from 1985 to 2017 shows the mean winter ice growth (mid-November to mid-April) simulated by the Los Alamos sea ice model (CICE) forced by NCEP-2 atmospheric reanalysis (a). Also shown are the mean 2 meters NCEP-2 air temperature averaged over the Arctic Ocean (b), cumulative freezing degree days (FDDs) (c) and CICE-simulated November ice thickness (d). See Stroeve et al. (2018) for more details.

Figure 5b. This time-series (a) from 1985 to 2017 shows the mean winter ice growth (mid-November to mid-April) simulated by the Los Alamos sea ice model (CICE) forced by the National Center for Environmental Prediction (NCEP-2) atmospheric reanalysis. Also shown are the mean 2 meters NCEP-2 air temperature averaged over the Arctic Ocean (b), cumulative freezing degree days (FDDs) (c), and CICE-simulated November ice thickness (d).

See Stroeve et al. (2018) for more details.
High-resolution image

The last three winters have seen air temperatures at the North Pole surge above 0 degrees Celsius (32 degrees Fahrenheit). While heat transport associated with individual storms can result in high air temperatures persisting over several days, a more important metric in regard to how winter warming impacts the sea ice cover is the cumulative number of freezing degree days. This is defined as the number of days below freezing multiplied by the magnitude of the temperatures below the freezing point. Widespread reductions in the total number of freezing degree days (as compared to average) are apparent for the last three winters, being most pronounced this past winter (Figure 5a).

Previous studies evaluated how the low number of cumulative freezing degree days in the 2015 to 2016 winter over the Barents and Kara Seas impacted the ice thickness and sea ice extent in that region. A newer study looks at the effects of warm winters for a larger area. NSIDC scientist Julienne Stroeve found that in response to the warm winter of 2016 to 2017, ice growth over the Arctic Ocean was likely reduced by 13 centimeters (5 inches). Generally, one does not expect variations in winter air temperature to have a significant impact on winter ice growth—temperatures still generally remain well below freezing and the rate at which ice grows (thickens) is greater for thin ice than thick ice. Thus, despite an overall increase in winter air temperatures, thermodynamic ice growth over winter has generally increased in tandem with thinning at the end of summer (Figure 5b). However, since 2012, this relationship appears to be changing. Overall winter ice growth in the 2016 to 2017 winter was similar to that in 2003, despite having a mean November ice thickness well below that seen in 2003. A similar analysis is not yet available for the 2017 to 2018 winter, but given the very warm conditions, it is likely that thermodynamic ice growth was reduced compared to average.

Unusual polynya opening north of Greenland

Figure6_adj

Figure 6a. This sequence of high-resolution images from the NASA Advanced Microwave Scanning Radiometer 2 (AMSR2) show the formation of a large polynya north of Greenland.

Credit: J. Stroeve, National Snow and Ice Data Center
High-resolution image

Figure6b. This graph shows average daily temperatures at Cape Morris Jesup, Greenland’s northernmost station. Credit:

Figure 6b. This graph shows average daily temperatures at Cape Morris Jesup, Greenland’s northernmost station.

Credit: J. Stroeve, National Snow and Ice Data Center
High-resolution image

During the middle of February, a large polynya opened north of Greenland and persisted through the first week of March (Figure 6a). Development of the polynya was driven in part by strong winds from the south and unusually high air temperatures. On February 24, during the peak of the polynya opening, air temperatures at Cape Morris Jesup, Greenland’s northernmost station, surged well above freezing, reaching 6.1 degrees Celsius (43 degrees Fahrenheit), while the daily average temperature hovered just above freezing (Figure 6b). Such periods of extremely warm winter temperatures have been unusual since the beginning of the Cape Morris Jesup record in 1981. During the month of February, only a few years exhibited hourly air temperatures rising above 0 degrees Celsius (32 degrees Fahrenheit): once in 1997, five times in 2011, seven in 2017 and 59 times in 2018.

References

Beitsch, A., L. Kaleschke, and S. Kern. 2014. Investigating high-resolution AMSR2 sea ice concentrations during the February 2013 fracture event in the Beaufort Sea. Remote Sensing 6, 3841-3856, doi.org/10.3390/rs6053841.

Boisvert, L.N., A.A. Petty, and J. Stroeve. 2016. The impact of the extreme winter 2015/16 Arctic cyclone on the Barents–Kara Seas, Bulletin of the American Meteorological Society, doi:10.1175/MWR-D-16-0234.1.

Ricker, R., S. Hendricks, F. Girard-Ardhuin, L. Kaleschke, C. Lique, X. Tian-Kunze, M. Nicolaus, and T. Krumpen. 2017a. Satellite observed drop of Arctic sea ice growth in winter 2015-2015, Geophysical Research Letters, doi:10.1002/2016GL072244.

Stroeve, J., D. Schroeder, M. Tsamados, and D. Feltham. 2018. Warm winter, thin ice? The Cryosphere, doi:10.5194/tc-2017-287, accepted.

Further reading

Thompson, A. “Shock and thaw—Alaskan sea ice just took a steep, unprecedented dive.” Scientific American. https://www.scientificamerican.com/article/shock-and-thaw-alaskan-sea-ice-just-took-a-steep-unprecedented-dive.

Hansen, K. “Historic low sea ice in the Bering Sea.” NASA Earth Observatory. https://earthobservatory.nasa.gov/IOTD/view.php?id=92084.

2018 winter Arctic sea ice: Bering down

The 2018 winter sea ice maximum has passed, and the melt season has begun. The most notable aspect of the 2017 to 2018 winter ice extent was the persistently low ice extent in the Bering Sea. While December, January, and February were characterized by very warm conditions over the Arctic, March temperatures were mixed, with cool conditions over the Eurasian side and moderately warm conditions over the North American side.

Overview of conditions

Figure 1. Arctic sea ice extent for March 2018 was 14.3 million square kilometers (5.52 million square miles). The magenta line shows the 1981 to 2010 average extent for that month.

Figure 1. Arctic sea ice extent for March 2018 was 14.30 million square kilometers (5.52 million square miles). The magenta line shows the 1981 to 2010 average extent for the month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent for March 2018 averaged 14.30 million square kilometers (5.52 million square miles), the second lowest in the 1979 to 2018 satellite record. This was 1.13 million square kilometers (436,300 square miles) below the 1981 to 2010 average and 30,000 square kilometers (11,600 square miles) above the record low March extent in 2017. Extent at the end of the month was far below average in the Bering Sea, as it has been for the past several months, and slightly below average in the far northern Atlantic Ocean and Barents Sea. Ice extent was slightly above average in the Sea of Okhotsk.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of April 4, 2018, along with daily ice extent data for four previous years, and the record low year. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2011 to 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data.

Figure 2a. The graph above shows Arctic sea ice extent as of April 4, 2018, along with daily ice extent data for four previous years, and the record low year. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2011 to 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Figure 2b. This plot shows the departure from average air temperatures at the 925 hPa level in degrees Celsius in the Arctic for March 2018. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Figure 2b. This plot shows departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for March 2018. Yellows and reds indicate higher than average temperature; blues and purples indicate lower than average temperature.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Figure 2c. This plot shows the average sea level pressures in the Arctic (in millibars) at the 925 hPa level for March 2018. Yellows and reds indicate higher than average air pressures; blues and purples indicate lower than average air pressures.

Figure 2c. This plot shows the average sea level pressure in the Arctic at the 925 hPa level, in millibars, for March 2018. Yellows and reds indicate higher than average air pressure; blues and purples indicate lower than average air pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Overall, ice extent for March 2018 changed little. Extent reached the annual maximum on March 17 and declined by March 31 to nearly the same level as at the beginning of the month. Ice loss following the seasonal maximum has been almost entirely restricted to the Bering Sea and the Sea of Okhotsk, with slight increases in extent in the Barents Sea and near Svalbard.

Air temperatures at the 925 hPa level (about 2,500 feet above sea level) were 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) higher than average in regions near Greenland and Alaska. Cooler conditions prevailed over Scandinavia, the Kara Sea, and far eastern Siberia, where temperatures were generally 4 to 7 degrees Celsius (7 to 13 degrees Fahrenheit) below average.

Higher than average sea level pressure was present over the western Arctic, including Canada, the Beaufort Sea, and Greenland, while lower than average sea level pressure prevailed over most of Europe and Siberia. This pattern was associated with winds from the south in the Bering Sea and Alaska, helping to push ice toward the pole. Conversely, over Scandinavia and the Barents Sea this pressure pattern resulted in winds from the northeast that pushed Arctic air onto the northern Eurasian landmass leading to colder air temperatures.

The Arctic Oscillation (AO), an indicator for general wind, precipitation, and temperature patterns in the Arctic, was strongly negative in early March, reflecting the higher than average sea level pressure in the western Arctic. This negative phase is characterized by a weakening of the circumpolar wind pattern, a pattern that favors cold air outbreaks over much of the United States as well as parts of Europe and Asia.

March 2018 compared to previous years

Figure 3. Monthly March ice extent for 1979 to 201X shows a decline of 2.7 percent per decade.||Credit: National Snow and Ice Data Center

Figure 3. Monthly March ice extent for 1979 to 2018 shows a decline of 2.7 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

The linear rate of decline for March ice extent is 42,200 square kilometers (16,400 square miles) per year, or 2.7 percent per decade relative to the 1981 to 2010 average.

Review of winter season 2017 to 2018

Figure 4. This plot shows the departure from average air temperatures in the Arctic at the 925 hPa level, in degrees Celsius, for December 2017 and January and February in 2018. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.||Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division| High-resolution image

Figure 4. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for December 2017 and January and February in 2018. Yellows and reds indicate higher than average temperature; blues and purples indicate lower than average temperature.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Unusually warm conditions and some prominent warm air intrusions characterized the 2017 to 2018 winter over the Arctic Ocean. Mean air temperature for the months of December, January, and February combined (the climatological winter season) was as much as 7 degrees Celsius (13 degrees Fahrenheit) higher than average, and nearly the entire Arctic Ocean was 4 degrees Celsius (7 degrees Fahrenheit) higher than average. This is the fourth year in a row that unusual jet stream patterns have led to warm air intrusions over the Arctic Ocean. However, some Arctic and subarctic land areas experienced unusually cold periods during the winter. Recent studies show that the frequency and intensity of warm air intrusions has increased in the last few years, particularly in the Atlantic sector, helping to reduce ice growth in the Barents Sea. The winter of 2017 to 2018 marks the second year in a row of pronounced warming events in the Pacific sector.

Deep snow in Russia and Europe

Figure 5. These images show the Northern Hemisphere water equivalent of snow cover in millimeters (top) and the Northern Hemisphere Total snow mass from October 2017 to March 31, 2018, in gigatons.

Figure 5. These images show Northern Hemisphere water equivalent of snow cover in millimeters (top) and Northern Hemisphere total snow mass in gigatons (bottom) from October 2017 to March 31, 2018.

Credit: GlobSnow Project and the Finnish Meteorological Institute
High-resolution image

Snow cover extent on the land masses surrounding the Arctic Ocean was average this past winter. However, an analysis of the snow cover thickness and density showed that the total snow mass this past winter was high. Estimates of total snow mass as of March 31 showed that the Northern Hemisphere had nearly 700 billion tons more snow this winter than the 1982 to 2012 average. Many areas of Russia and northern Europe had more than 150 millimeters (6 inches) of water-equivalent on the ground, present as deep snow cover. Snow extent had been above average the entire autumn-winter season but grew to exceptional levels beginning in February. Although the total snow mass has begun to decrease, it is still far above average. The analysis is based on many sources of snow and snow depth data, including passive microwave data produced by NSIDC (EASE-Grid Snow Water Equivalent and Daily Snow Cover), and data derived from several other groups from the European Space Agency and the National Oceanographic and Atmospheric Administration.

Sea ice drift in the Arctic Ocean

Figure 6. This plot shows monthly average sea ice motion in the Arctic for the months of January, February, and March in 2018. Credit: NSIDC courtesy Ocean and Sea Ice Satellite Application Facility (OSI-SAF)

Figure 6. This plot shows monthly average sea ice motion in the Arctic, in centimeters per second, for the months of January, February, and March in 2018.

Credit: Alek Petty/NASA Goddard Space Flight Center (GSFC) and the Ocean and Sea Ice Satellite Application Facility (OSI-SAF)
High-resolution image

Plots of monthly average sea ice motion for January, February, and March 2018 reveal pronounced changes in drift direction, since sea ice movement is largely controlled by winds, and therefore storms and pressure patterns. The maps include averages of sea surface temperature outside of the ice-covered area, and indicate that the surface of both the northern Pacific and northern Atlantic were substantially warmer relative to a 1982 to 2015 reference period. Strong Beaufort Gyre and Transpolar Drift patterns were present for January and March of 2018. Ice motion and sea surface temperature data are based on a multi-sensor estimate created by the Ocean and Sea Ice Satellite Application Facility (OSI-SAF), a European meteorological consortium.

Seasonal increase in Antarctic sea ice

After reaching a minimum extent for the year on February 20 and 21, Antarctic sea ice grew rapidly in March 2018. Sea ice extent averaged 3.53 million square kilometers (1.36 million square miles) for the month, not far below the 1981 to 2010 average of 4.03 million square kilometers (1.56 million square miles). Growth was especially rapid in the Amundsen and Ross Seas, nearly erasing the area of below-average sea ice extent that had been in the eastern Ross Sea and western Amundsen in early March.

Rapid sea ice growth in the Amundsen and eastern Ross Seas was reflected in temperatures at the 925 hPa level that were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below average across the Pine Island Bay region. This is likely related to cool winds from the south coming up against the west side of a low-pressure area over the Bellingshausen Sea. By comparison, temperatures 2.5 to 4.5 degrees Celsius (4 to 8 degrees Fahrenheit) higher than average were the rule over much of the continental interior from Dronning Maud Land to northern Victoria Land along the Transantarctic Mountains. The index of the strength of the circumpolar vortex (or Southern Annular Mode) was near-neutral for March.

References

Boisvert, L. N., A. A. Petty, and J. Stroeve. 2016. The Impact of the Extreme Winter 2015/16 Arctic Cyclone on the Barents–Kara Seas, Bulletin of the American Meteorological Society, doi:10.1175/MWR-D-16-0234.1.

Graham, R. M., L. Cohen, A. A. Petty, L. N. Boisvert, A. Rinke, S. R. Hudson, M. Nicolaus, and M. A. Granskog. 2017. Increasing frequency and duration of Arctic winter warming events, Geophysical Research Letters, 44, 6974–6983, doi:10.1002/2017GL073395.

Ricker, R., S. Hendricks, F. Girard-Ardhuin, L. Kaleschke, C. Lique, X. Tian-Kunze, M. Nicolaus, and T. Krumpen. 2017. Satellite observed drop of Arctic sea ice growth in winter 2015-2015, Geophysical Research Letters, doi:10.1002/2016GL072244.

Rinke, A., M. Maturilli, R. M. Graham, H. Matthes, D. Handorf, L. Cohen, S. R. Hudson, and J. C. Moore. 2017. Extreme cyclone events in the Arctic: Wintertime variability and trends , Environmental Research Letters, 12 (9), 094006, doi:10.1088/1748-9326/aa7def.

Correction

On April 20, we revised a sentence under the section Seasonal increase in Antarctic sea ice. The sentence originally read “Growth was especially rapid in the Amundsen and eastern Ross Sea, where sea ice was nearly absent at the time of the minimum extent, and along the East Antarctic coast, where many areas now exceed the daily median extent for the end of March.” We revised it to “Growth was especially rapid in the Amundsen and Ross Seas, nearly erasing the area of below-average sea ice extent that had been in the eastern Ross Sea and western Amundsen in early March.”

 

Arctic sea ice maximum at second lowest in the satellite record

Arctic sea ice appears to have reached its annual maximum extent on March 17. This is the second lowest Arctic maximum in the 39-year satellite record. The four lowest maximum extents in the satellite record have all occurred in the past four years. NSIDC will post a detailed analysis of the 2017 to 2018 winter sea ice conditions in our regular monthly post in early April.

Overview of conditions

Figure 1. Arctic sea ice extent for March 17, 2018 was 14.48 million square kilometers (5.59 million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data||Credit: National Snow and Ice Data Center|High-resolution image

Figure 1. Arctic sea ice extent for March 17, 2018 was 14.48 million square kilometers (5.59 million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

On March 17, 2018, Arctic sea ice likely reached its maximum extent for the year, at 14.48 million square kilometers (5.59 million square miles), the second lowest in the 39-year satellite record, falling just behind 2017. This year’s maximum extent is 1.16 million square kilometers (448,000 square miles) below the 1981 to 2010 average maximum of 15.64 million square kilometers (6.04 million square miles).

The four lowest seasonal maxima have all occurred during the last four years. The 2018 maximum is 60,000 square kilometers (23,200 square miles) above the record low maximum that occurred on March 7, 2017; 40,000 square kilometers (15,400 square miles) below the 2015 and 2016 maxima (now tied for third lowest); and is 190,000 square kilometers (73,400 square miles) below the 2011 maximum, which is now fifth lowest.

In March 2017, we reported a new record maximum being set, with 2016 sliding to the second lowest, and 2015 the third lowest. In November 2017, we updated our calculation of the monthly average sea ice extent in the NSIDC Sea Ice Index, resulting in 2016 tying with 2015.

The date of the maximum this year, March 17, was five days later than normal compared to the 1981 to 2010 median date of March 12.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of March 22, 2018, along with daily ice extent data for five previous years. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2012 in magenta, and 2011 to 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data.

Figure 2. The graph above shows Arctic sea ice extent as of March 22, 2018, along with daily ice extent data for four previous years and the record low year. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in magenta, and the record low year 2011 to 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

The ice growth season ended with very low sea ice extents in the Bering Sea in the Pacific side of the Arctic, and in the Barents Sea in the Atlantic side of the Arctic. The regions of reduced ice cover reflect the combined influences of late autumn freeze-up as well as persistent high air temperatures throughout the winter. Freeze-up was especially late in the Chukchi Sea, due in part to the effects of strong ocean heat transport into the area through the Bering Strait. February then saw an early retreat of sea ice in the Bering Sea. Sea ice extent on the Atlantic side remained below average throughout the winter, which also appears linked to warm ocean waters. While air temperatures at the 925 hPa level (about 2,500 feet above sea level) remained well above average through most of winter, February saw an extreme heat wave over the Arctic Ocean. This is the fourth winter in a row that such heat waves have been recorded over the Arctic Ocean.

A late spurt in sea ice growth just prior to the maximum occurred in the Barents Sea near Novaya Zemlya; sea ice retreat just after the maximum was led by ice loss in the Bering Sea.

Table 1. Ten lowest maximum Arctic sea ice extents (satellite record, 1979 to present)

Rank Year In millions of square kilometers In millions of square miles Date
1 2017 14.42 5.57 March 7
2 2018 14.48 5.59 March 17
3 2015 14.52 5.61 February 25
3 2016 14.52 5.61 March 24
5 2011 14.67 5.66 March 9
5 2006 14.68 5.67 March 12
7 2007 14.77 5.7 March 12
8 2005 14.95 5.77 March 12
8 2014 14.96 5.78 March 21
10 2009 15.17 5.84 March 5

The Antarctic minimum

As noted in our previous post, in the Southern Hemisphere, sea ice reached its minimum extent for the year on February 20 and 21, at 2.18 million square kilometers (842,000 square miles). This year’s minimum extent was the second lowest in the satellite record, 70,000 square kilometers (27,00 square miles) above the record low set on March 3, 2017. The Antarctic minimum extent is 670,000 square kilometers (259,000 square miles) below the 1981 to 2010 average minimum of 2.85 million square kilometers (1.10 million square miles).

The February 20 and 21 timing of the minimum (the same extent was recorded on both dates) was just slightly earlier than the 1981 to 2010 median date of February 24 for the minimum. Over the satellite record, the Antarctic minimum has occurred as early as February 15 and as late as March 6.

Compared to the Arctic, air temperatures over the sea ice regions of Antarctica over the past season (austral summer) have been closer to their climatological average, hovering within 2 degrees Celsius (4 degrees Fahrenheit) of the 1981 to 2010 average. Relatively rapid and early growth of ice along the eastern Weddell Sea ice edge led the beginning of the autumn sea ice expansion.

Final analysis pending

Please note this is a preliminary announcement. At the beginning of April, NSIDC scientists will release a full analysis of winter conditions in the Arctic, along with monthly data for March. For more information about the maximum extent and what it means, see the NSIDC Icelights post, the Arctic sea ice maximum.

A warm approach to the equinox

As temperatures at the North Pole approached the melting point at the end of February, Arctic sea ice extent tracked at record low levels for this time of year. Extent was low on both the Atlantic and Pacific sides of the Arctic, with open water areas expanding rapidly in the Bering Sea during the latter half of the month. On the other side of the globe, Antarctic sea ice has reached its minimum extent for the year, the second lowest in the satellite record.

Overview of conditions

Figure 1. Arctic sea ice extent for February 2018 was 13.95 million square kilometers (5.39 million square miles). The magenta line shows the 1981 to 2010 average extent for that month.

Figure 1. Arctic sea ice extent for February 2018 was 13.95 million square kilometers (5.39 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Winter continues to be mild over the Arctic Ocean. Sea ice extent remained at record low daily levels for the month. Arctic sea ice extent for February 2018 averaged 13.95 million square kilometers (5.39 million square miles). This is the lowest monthly average  recorded for February, 1.35 million square kilometers (521,000 square miles) below the 1981 to 2010 average and 160,000 square kilometers (62,000) below the previous record low monthly average in 2017.

Extent was especially low in the Bering Sea where sea ice declined during the first three weeks of the month. The eastern part of the Bering Sea was largely ice-free for most of the month; extent was low on the western side, with the ice edge further north than normal. In the Chukchi Sea, extent also retreated during part of February, with open water developing north of the Bering Strait on both the Siberian and Alaskan coasts. As seen all winter, ice extent continued to be below average in the Barents Sea, and at the end of February, a wedge of open water formed north of Svalbard that extended well into the Arctic Ocean.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of March 4, 2018, along with daily ice extent data for four previous years. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2011 to 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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Figure 2b. This plot shows the average sea level pressures at the 925 hPa level for February 2018. Yellows and reds indicate higher than average air pressures; blues and purples indicate lower than average air pressures.

Figure 2b. This plot shows the average sea level pressures at the 925 hPa level for February 2018. Yellows and reds indicate higher than average air pressures; blues and purples indicate lower than average air pressures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
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Figure 2c. This figure shows differences from the average in temperature in degrees Celsius and in addition to wind conditions for the period February 22 to 26, 2018. In addition, the North Atlantic Oscillation (NAO) index is shown in the lower left. This is a measure of the strength of the westerly winds in the North Atlantic. When the index is negative, the flow is wavier, which increases the probability of transport of warm air to Greenland from the south.

Figure 2c. This figure shows differences from average temperature in degrees Celsius, and wind conditions for the period February 22 to 26, 2018. In addition, the North Atlantic Oscillation (NAO) index is shown in the lower left. This is a measure of the strength of the westerly winds in the North Atlantic. When the index is negative, the flow is wavier, which increases the probability of transport of warm air to Greenland from the south.

Credit: European Centre for Medium-Range Weather Forecasts (ECMWF) IFS forecast model
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Low pressure centered just east of the Kamchatka Peninsula and high pressure centered over Alaska and the Yukon during February set up southerly winds that brought warm air and warm ocean waters into the Pacific side of the Arctic Ocean, impeding southward ice growth. This helps to explain the rapid loss of ice extent in the Bering Sea and the ice-free regions within the Chukchi Sea during the month. The warm air intrusion is evident in the 925 mb air temperatures, with monthly temperatures 10 to 12 degrees Celsius (18 to 22 degrees Fahrenheit) above average in the Chukchi and Bering Sea.

On the Atlantic side, low pressure off the southeast coast of Greenland and high pressure over northern Eurasia helped to funnel warm winds into the region and may have also enhanced the northward transport of oceanic heat. At the end of the month, this atmospheric circulation pattern was particularly strong, associated with a remarkable inflow of warm air from the south, raising the temperatures near the North Pole to above freezing, around 20 to 30 degrees Celsius (36 to 54 degrees Fahrenheit) above average. Air temperatures at Cape Morris Jesup in northern Greenland (83°37’N, 33°22’W) exceeded 0 degrees Celsius for several hours and open water formed to the north of Greenland at the end of the month. This is the third winter in a row in which extreme heat waves have been recorded over the Arctic Ocean. A study published last year by Robert Graham from the Norwegian Polar Institute showed that recent warm winters represent a trend towards increased duration and intensity of winter warming events within the central Arctic. While the Arctic has been relatively warm for this time of year, northern Europe was hit by extreme cold conditions at the end of February.

February 2018 compared to previous years

Figure 3. Monthly 2018 ice extent for 1979 to 2018 shows a decline of 3.1 percent per decade.

Figure 3. Monthly 2018 ice extent for 1979 to 2018 shows a decline of 3.1 percent per decade.

Credit: National Snow and Ice Data Center
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The linear rate of decline for February is 47,000 square kilometers per year (18,000 square miles per year), or 3.1 percent per decade.

Late freeze-up

freeze average and anomaly plots

Figure 4. These graphs show the average Arctic Ocean ice freeze-up dates for 1979 to 2017 (top) and the number of days that freeze-up occurred earlier (cool colors) or later (warm colors) than average (bottom).

Credit: J. Miller, NASA Goddard Space Flight Center
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This year, the freeze-up started earlier than average over much of the central Arctic Ocean, near average within Hudson and Baffin Bays, but significantly later than average elsewhere. Freeze-up was delayed by more than a month later than average within the Chukchi and Bering Seas on the Pacific side, and within the Barents and East Greenland Seas on the Atlantic side. In these regions freeze-up happened after December. Later freeze-up impacts sea ice thickness, reducing the number of days over which sea ice can grow during winter.

Winter navigation in the Arctic without an icebreaker

Figure 4. This figure shows the distribution of Arctic sea ice according to stage of development, , as of February 22, 2018. Pink shows new ice; purple shows young ice; blue shows first year thin ice; orange shows first year medium ice, red shows first year thick ice, brown shows old ice, and while shows glacial ice.

Figure 5. This figure shows the distribution of Arctic sea ice according to stage of development, , as of February 22, 2018. Pink shows new ice; purple shows young ice; blue shows first year thin ice; orange shows first year medium ice, red shows first year thick ice, brown shows old ice, and while shows glacial ice.

Credit: U.S. National Ice Center
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The Arctic Ocean is becoming more accessible for shipping. Most of the increase in commercial shipping traffic has been during summer, primarily through the Northern Sea Route along the coast of Siberia. However, this February a commercial tanker, the Eduard Toll, made the first crossing of the Northern Sea Route in winter. Improvements in ship-building and the development of ice-strengthened hull technology is a major factor in enabling winter access. Previous ice-strengthened ships could only navigate safely through 0.5 meter thick ice, compared to the 1.8 meter thick ice that the Eduard Toll cruised through. A fleet of six ships with similar technology is being constructed by a South Korean shipbuilder.

While the Northern Sea Route has tended to be dominated by first-year ice, which typically reaches a maximum of around 2 meters, thicker (3- to 4-meter) multi-year ice would be a hazard even to the newer, stronger ships. According to analysis by the U.S. National Ice Center, this year’s old ice (multi-year ice) has pulled completely away from the coast and the Northern Sea Route is dominated by first-year medium (0.7- to 1.2-meter) or first-year thick (1.2- to 2-meter) ice.

Opposite pole, same near-record low extent

Figure 6. The graph above shows Antarctic sea ice extent as of March 1, 2018, along with daily ice extent data for four previous years. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2011 to 2012 in dotted magenta. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data.

Figure 6a. The graph above shows Antarctic sea ice extent as of March 1, 2018, along with daily ice extent data for four previous years. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2011 to 2012 in dotted magenta. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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Figure 6b. This figure shows Antarctic sea ice extent for February 28, 2018. Sea Ice Index data. About the data||Credit: National Snow and Ice Data Center|High-resolution image

Figure 6b. This figure shows Antarctic sea ice extent for February 28, 2018. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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In the Antarctic, sea ice extent reached its daily seasonal minimum, 2.18 million square kilometers (842,000 square miles), on February 20 and 21. This is the second lowest minimum extent in the satellite record, 70,000 square kilometers (27,000 square miles) above the record low, which was set on March 3, 2017. The February average was 2.29 million square kilometers (884,000 square miles), second lowest in the satellite record, and 20,000 square kilometers (7,700 square miles) above the record low February in 2017.

Sea ice in the Antarctic is highly variable from year to year—much more so than in the Arctic. This is clearly seen in the February extent values, where low 2011 values were followed by record or near-record highs in 2013, 2014, and 2015. This was then followed by record or near-record lows in 2017 and this year.

Sea ice extent is particularly low in the Ross and western Amundsen Sea region, and along the southern reaches of the Bellingshausen Sea. Patchy sea ice areas along the East Antarctic coast are near-average in extent.

Further reading

Graham, R. M., L. Cohen, A. A. Petty, L. N. Boisvert, A. Rinke, S.R. Hudson, M. Nicolaus, and M. A. Granskog. 2017. Increasing frequency and duration of Arctic winter warming events, Geophys. Res. Lett., 16, 6974-6983, doi:10.1002/2017GL073395.

Kretschmer, M., D. Coumou, L. Agel, M. Barlow, E. Tziperman, and J. Cohen. 2017. More persistent weak stratospheric polar vortex states linked to cold extremes, Bull. Amer. Meteor. Soc., doi:10.1175/BAMS-D-16-0259.1.

 

 

Sea ice tracking low in both hemispheres

January of 2018 began and ended with satellite-era record lows in Arctic sea ice extent, resulting in a new record low for the month. Combined with low ice extent in the Antarctic, global sea ice extent is also at a record low.

Overview of conditions

sea ice extent map

Figure 1. Arctic sea ice extent for January 2018 was 13.06 million square kilometers (5.04 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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The new year was heralded by a week of record low daily ice extents, with the January average beating out 2017 for a new record low. Ice grew through the month at near-average rates, and in the middle of the month daily extents were higher than for 2017. However, by the end of January, extent was again tracking below 2017. The monthly average extent of 13.06 million square kilometers (5.04 million square miles) was 1.36 million square kilometers (525,000 square miles) below the 1981 to 2010 average, and 110,000 square kilometers (42,500 square miles) below the previous record low monthly average in 2017.

The pattern seen in previous months continued, with below average extent in the Barents and Kara Seas, as well as within the Bering Sea. The ice edge remained nearly constant throughout the month within the Barents Sea, and slightly retreated in the East Greenland Sea. By contrast, extent increased in the Gulf of St. Lawrence, off the coast of Newfoundland, in the eastern Bering Sea and the Sea of Okhotsk. Compared to 2017, at the end of the month, ice was less extensive in the western Bering Sea, the Sea of Okhotsk and north of Svalbard, more extensive in the eastern Bering Sea and in the Gulf of St. Lawrence. Overall, the Arctic gained 1.42 million square kilometers (548,000 square miles) of ice during January 2018.

Conditions in context

extent timeseries

Figure 2a. The graph above shows Arctic sea ice extent as of February 5, 2018, along with daily ice extent data for five previous years. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2012 to 2013 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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airtemp

Figure 2b. The plot shows air temperatures in degrees Celsius in the Arctic as difference from average for January 2018. Yellows, oranges, and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA/ESRL Physical Sciences Division
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Air temperatures at the 925 hPa level (about 2,500 feet above sea level) remained unusually high over the Arctic Ocean (Figure 2b). Nearly all of the region was at least 3 degrees Celsius (5 degrees Fahrenheit) or more above average. The largest departures from average of more than 9 degrees Celsius (16 degrees Fahrenheit) were over the Kara and Barents Seas, centered near Svalbard. On the Pacific side, air temperatures were about 5 degrees Celsius (9 degrees Fahrenheit) above average. By contrast, 925 hPa temperatures over Siberia were up to 4 degrees Celsius (7 degrees Fahrenheit) below average. The warmth over the Arctic Ocean appears to result partly from a pattern of atmospheric circulation bringing in southerly air, and partly from the release of heat into the atmosphere from open water areas. Sea level pressure was higher than average over the central Arctic Ocean, stretching towards Siberia. This pattern, coupled with below average sea level pressure over the Chukchi and Bering seas, helped to move warm air from Eurasia over the central Arctic Ocean.

Ice growth for January averaged 37,000 square kilometers (14,000 square miles) per day, close to the average rate for the month of 42,700 square kilometers per day (16,486 square miles per day). In the Barents Sea, the ice extent was the second lowest during the satellite data record. Ice conditions in this region of the Arctic are increasingly viewed as important in having downstream effects on atmospheric circulation. These proposed links include northward expansion of the Siberian High and cooling over northern Eurasia.

January 2018 compared to previous years

extent trend graph

Figure 3. Monthly January ice extent for 1979 to 2018 shows a decline of 3.3 percent per decade.

Credit: National Snow and Ice Data Center
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The linear rate of decline for January is 47,700 square kilometers (18,400 square miles) per year, or 3.3 percent per decade.

Engaging stakeholders in sea ice forecasting

tourism graphs

Figure 4. These graphs show changes in polar tourism based on membership in the Association of Arctic Expedition Cruise Operators (AECO, top), and by the number and type of Arctic vessels operated or managed (bottom).

Credit: Kelvin Murray, Director, Expedition Operations EYOS Expeditions
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Uncertainty about future sea ice conditions presents challenges to industry, policymakers, and planners responsible for economic, safety, and risk mitigation decisions. The ability to accurately forecast the extent and duration of sea ice on different timescales is relevant to a wide range of Arctic maritime activities. While there have been considerable advances in sea ice forecasting over the past decade, it remains unclear how well end users are able to utilize these products and services in their planning. In response, the Sea Ice Prediction Network, in collaboration with several sponsors, held a workshop at the Arctic Frontiers Conference in Tromsø, Norway to foster dialogue between stakeholders and sea ice forecasters.

Conference attendees recognized that the sea ice forecasting community and users of these forecasts need a common language. Often forecast users do not understand the data presented by forecasters, nor do they have the skills to interpret the complex data products. Most marine operators in the Arctic require accurate daily to short-term (< 72 hours) information on the sea ice edge and near-ice-edge concentration. Forecast users often want additional information such as ice strength, ice thickness and ice drift. These data need to be accessed in a user-friendly format that can be easily downloaded (e.g., to a ship at sea). Typically, ice charts from national ice centers or high-resolution Synthetic Aperture Radar image maps are used for describing and analyzing sea ice for real-time navigation.

Longer-term seasonal ice forecasts are potentially useful to the polar marine industry but are not yet being relied upon. While improving, the uncertainty in these forecasts has not been clearly communicated. Nevertheless, logistics planners are interested in using longer-term forecasts, mostly to augment or extend more timely data or in-house diagnostics. Tour operators in particular desire seasonal and even two- to three-year forecasts so that they can plan what to offer their customers. Along with the increase in polar tourism (Figure 4), there is also significant industry traffic in the European Arctic, the Northwest Passage and some areas in the Northern Sea Route. Due to the decreasing ice cover, we can expect an extension of the seasonal activity, with ships embarking earlier and ending their journeys later than in previous years. This underscores the need for accurate forecasting, extending to the more variable shoulder seasons of Arctic sea ice.

Importance of ice drift

Figure 5. The top figure shows the location of the R/V Lance during the N-ICE2015 expedition (pink lines) with aircraft flight lines shown in black and blue. The bottom figure shows a time series of wind speed and direction, together with rates of ice divergence (blue line) and shear (purple line). Figure from Itkin et al. 2017.

Credit: Norwegian Polar Institute
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As the Arctic sea ice cover continues to thin, convergent sea ice motion can more readily pile up ice into large ridges. Such ridges can be hazardous to marine activities in the Arctic. Divergent ice motion produces openings in the ice called leads, where new ice can readily grow. Winds are the main driver for both ridging and lead formation. A single storm event can lead to significant redistribution of sea ice mass through ridging and new leads. As part of the Norwegian Young Sea ICE (N-ICE2015) expedition, colleagues at the Norwegian Polar Institute made detailed sea ice thickness and ice drift observations before and after a storm in an area north of Svalbard (Figure 5). Results showed that about 1.3 percent of the level sea ice volume was pressed together into ridges. Combined with new ice formation in leads, the overall ice volume increased by 0.5 percent. While this is a small number, sea ice in the North Atlantic is typically impacted by 10 to 20 storms each winter, which could account for 5 to 10 percent of ice volume each year.

Antarctic sea ice also low, leading to low global sea ice extent

In the Southern Hemisphere, after January 11 sea ice began tracking low, leading to a January average extent that was the second lowest on record. The lowest extent for this time of year was in 2017. Extent is below average in the Ross Sea and the West Amundsen Seas, while elsewhere extent remains close to average. The low ice extent is puzzling, given that air temperatures at the 925 hPa level are near average or below average (relative to the 1981 to 2010 period) over much of the Southern Ocean. The Weddell and Amundsen Seas were 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) below average. Slightly above-average temperatures were the rule in the northwestern Ross Sea.

Further reading

Itkin, P., Spreen, G., Hvidegaard, S. M., Skourup, H., Wilkinson, J., Gerland, S., & Granskog, M. A. 2018. Contribution of deformation to sea ice mass balance: A case study from an N-ICE2015 storm. Geophysical Research Letters, 45. https://doi.org/10.1002/2017GL076056.

 

Baked Alaska and 2017 in review

Arctic sea ice extent in December 2017 was below average in both the far northern Atlantic and the Bering Sea, and notably high temperatures prevailed over most of the Arctic, especially over Central Alaska. We look back at the year’s events, and examine Arctic sea ice trends since 1850 based on a new compilation of data from maps, ship reports, and other records.

Overview of conditions

Figure 1. Arctic sea ice extent for December 2016 was 11.75 million square kilometers (4.54 million square miles). The magenta line shows the 1981 to 2010 average extent for that month.

Figure 1. Arctic sea ice extent for December 2017 was 11.75 million square kilometers (4.54 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Arctic sea ice extent for December 2017 averaged 11.75 million square kilometers (4.54 million square miles), the second lowest in the 1979 to 2017 satellite record. This was 1.09 million square kilometers (420,900 square miles) below the 1981 to 2010 average and 280,000 square kilometers (108,100 square miles) above the record low December extent recorded in 2016. Extent at the end of the month was below average in the far northern Atlantic Ocean and Barents Sea, slightly above average in western Hudson Bay, and continued to be below average in the Bering and Chukchi Seas. Near-average conditions prevailed along the eastern coast of Greenland and in the Sea of Okhotsk.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of January 2, 2018, along with daily ice extent data for four previous years. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2014 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2012 to 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data.

Figure 2a. The graph above shows Arctic sea ice extent as of January 2, 2018, along with daily ice extent data for five previous years. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2014 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2012 to 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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Figure 2b. This plot shows the departure from average air temperatures at the 925 hPa level in degrees Celsius for December 2017. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.||Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division

Figure 2b. This plot shows the departure from average air temperatures at the 925 hPa level in degrees Celsius for December 2017. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
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Figure 2c. This plot shows the departure from average sea level pressures at the 925 hPa level in degrees Celsius for December 2018. Yellows and reds indicate higher than average air pressures; blues and purples indicate lower than average air pressures.|

Figure 2c. This plot shows the departure from average sea level pressures at the 925 hPa level in degrees Celsius for December 2018. Yellows and reds indicate higher than average air pressures; blues and purples indicate lower than average air pressures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Ice growth during December 2017 averaged 59,800 square kilometers (23,100 square miles) per day. This was fairly close to the average rate for the month of 64,100 square kilometers (24,800 square miles) per day. Ice growth in the Chukchi Sea (very late compared to previous years), the Kara Sea, and the eastern Hudson Bay areas were the main regions of change in December. In contrast, the ice edge slightly retreated in the Barents Sea near Franz Josef Land.

December air temperatures at the 925 hPa level (about 2,500 feet above sea level) throughout the Arctic Ocean were 2 to 6 degrees Celsius (4 to 11 degrees Fahrenheit) above average. Prominent warm spots were found over north Central Asia and Central Alaska (more than 10 degrees Celsius, or 18 degrees Fahrenheit above average), as well as over Svalbard and Central Siberia (nearly 6 degrees Celsius or 11 degrees Fahrenheit above average). Temperatures were 2 to 3 degrees Celsius (4 to 5 degrees Fahrenheit) below average in Eastern Siberia.

The air temperature pattern in December was similar to that seen in November, driven in part by the arrangement of high and low air pressure regions surrounding the Arctic. Below-average pressure over easternmost Siberia and above-average pressure over the Gulf of Alaska drove southwesterly winds into Central Alaska and the Yukon region. Warmth in the Central Arctic and in Svalbard was consistent with southerly winds arising from low pressure over Scandinavia and higher pressure in the Laptev Sea and Central Siberia.

The Arctic Oscillation (AO) is a key climate indicator for general wind, precipitation, and temperature patterns in the Arctic. The AO index was moderately positive through most of 2017, indicating a tendency toward strong circumpolar winds at high latitude and warm conditions in the mid-latitudes. December 2017 had a mix of conditions, resulting in a near-neutral AO state (as measured by the index).

December 2017 compared to previous years

Figure 3. Monthly December ice extent for 1979 to 2017 shows a decline of 3.7 percent per decade.

Figure 3. Monthly December ice extent for 1979 to 2017 shows a decline of 3.7 percent per decade.

Credit: National Snow and Ice Data Center
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The linear rate of sea ice decline for December is 47,400 square kilometers (18,300 square miles) per year or 3.7 percent per decade. Recall from our previous post that NSIDC has revised the way in which monthly average extents are computed, which has some impacts on computed trends.

2017 year in review

Figure 4. These figures show trends for sea ice-over dates in the Beaufort (top) and Chukchi (bottom) Seas.

Figure 4. These figures show trends for ice-over dates in the Beaufort (top) and Chukchi (bottom) Seas. Sea Ice Index data.

Credit: R. Thoman, NOAA
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The winter of 2016 to 2017 saw record low winter sea ice extent and higher than average temperatures. Indeed, the first four months of 2017 set or tied record low extents for the month. However, the melt season progressed somewhat slowly from May through July, as storminess and relatively cool conditions began to prevail. As such, sea ice extent at the seasonal minimum, on September 13, ended up as eighth lowest.

Assessments of sea ice thickness modeled by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS), as well as sea ice age near the seasonal minimum extent indicate that Arctic sea ice remains very low in overall volume. As the year ended, ice extent remained especially low in the Chukchi and Bering Seas. As discussed in an earlier post, the unusually early seasonal ice retreat in the Chukchi Sea this past summer likely relates to a strong inflow of oceanic heat into the region via the Bering Strait. With more heat in the upper ocean at summer’s end, it takes longer for sea ice to form in autumn and winter. Colleague Rick Thoman of the National Oceanic and Atmospheric Administration (NOAA) National Weather Service has assembled a time series of the ice-over dates in both the Chukchi and Beaufort Seas based on the satellite passive microwave record (Figure 4). The ice-over date is defined as the first day that the ice concentration exceeds 95 percent in the region. The trends towards later freeze up in both seas is striking. This has an impact on sea ice thickness as the growth season is shortened, which may lead to thinner ice by the end of winter. On the other hand, later freeze up also means less time for snow accumulation on the sea ice. Since sea ice grows faster for a thinner snowpack, this may partially offset the impacts of late ice formation.

A longer record of Arctic sea ice extent

Figure 5a. This figure shows departures from 1850 to 2013 calendar-month averages of Arctic sea ice extent as a function of year (x-axis) and calendar month (y-axis). The color bar at the right shows magnitudes of departures from the average.

Figure 5a. This figure shows departures from 1850 to 2013 calendar-month averages of Arctic sea ice extent as a function of year (x-axis) and calendar month (y-axis). The color bar at the right shows magnitudes of departures from the average.

Credit: J. E. Walsh, F. Fetterer, J. S. Stewart, W. L. Chapman. 2016. Geographical Review; after a figure by J. Stroeve, National Snow and Ice Data Center
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Figure 5b. These sea ice concentration maps compare the lowest September minimum Arctic sea ice extents for the periods 1850 to 1900, 1901 to 1950, 1951 to 2000, and 2000 to 2013.||Credit: F. Fetterer/National Snow and Ice Data Center, NOAA

Figure 5b. These sea ice concentration maps compare the lowest September minimum Arctic sea ice extents for the periods 1850 to 1900, 1901 to 1950, 1951 to 2000, and 2000 to 2013.

Credit: F. Fetterer/National Snow and Ice Data Center, NOAA
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Using a compilation of maps, ship reports, and other records, NOAA has published monthly estimates of Arctic sea ice extent spanning 1850 to 2013. While data in the earlier part of the record is limited, the carefully constructed time series helps to put the more recent satellite record in a longer-term context. Figure 5a shows the decline in extent over the period of satellite observations standing out prominently in comparison with the rest of the record, especially in late summer and early autumn. An earlier period of unusually low summer sea ice extent around 1937 to 1943 (as compared to the 1850 to 2013 average) did not extend to the winter season, and was followed by a few years of significantly higher-than-average summer ice extents. Early in the record (1850 to 1900), winter ice extent was not particularly elevated relative to the 1850 to 2013 average, but summer sea ice extent was quite a bit higher higher than the average. As another way to place recent conditions into a longer context using this data set, we show the years of the lowest September extent recorded within the 50-year periods 1850 to 1900, 1901 to 1950, 1951 to 2000, along with the lowest over the period 2000 to 2013 (Figure 5b). The decline in extent is apparent.

Low sea ice extent in the Antarctic

Figure 6. Antarctic sea ice extent for December 2017 was 9.34 million square kilometers (3.61 million square miles). The magenta line shows the 1981 to 2010 average extent for that month.

Figure 6. Antarctic sea ice extent for December 2017 was 9.34 million square kilometers (3.61 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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In the Southern Hemisphere, sea ice for December 2017 averaged 9.34 million square kilometers (3.61 million square miles) and was the fourth lowest in the satellite record. Sea ice extent was far below average in the eastern Weddell Sea, but above average in the northwestern Weddell Sea. The East Antarctic coastline had near-average ice extent. As the Southern Hemisphere entered into the summer months, sea ice declined steeply. Temperatures at the 925 hPa level were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) higher than average in Dronning Maud Land and the northern Ross Sea, and generally lower than average over the ice sheet. Near-average temperatures have prevailed over the fringing Southern Ocean. Pressures were slightly above average over the continent and below average in the surrounding ocean. Consistent with this pattern, the Southern Annular Mode index, a measure of the strength of westerly winds, was moderately positive for December.

Further reading

Walsh, J. E., F. Fetterer, J. S. Stewart, and W. L. Chapman. 2016. A database for depicting Arctic sea ice variations back to 1850. Geographical Review. doi: 10.1111/j.1931-0846.2016.12195.x.

Record low extent in the Chukchi Sea

November 2017 will be remembered not for total Arctic ice extent, which was the third lowest recorded over the period of satellite observations, but for the record low extent in the Chukchi Sea. This is a key area for Arctic Ocean access, and is an indicator of oceanographic influences on sea ice extent.

Overview of conditions

Figure 1. Arctic sea ice extent for XXXX 20XX was X.XX million square kilometers (X.XX million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data||Credit: National Snow and Ice Data Center|High-resolution image

Figure 1. Arctic sea ice extent for November 2017 was 9.46 million square kilometers (3.65 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent for November 2017 averaged 9.46 million square kilometers (3.65 million square miles), the third lowest in the 1979 to 2017 satellite record. This was 1.24 million square kilometers (479,000 square miles) below the 1981 to 2010 average and 830,000 square kilometers (321,000 square miles) above the record low November extent recorded in 2016. Extent at the end of the month was below average over the Atlantic side of the Arctic, primarily in the Barents and Kara Seas, slightly above average in western Hudson Bay, but far below average in the Chukchi Sea. This continues a pattern of below-average extent in this region that has persisted for the last year.

Conditions in context

timeseries graph

Figure 2. The graph above shows Arctic sea ice extent as of December 3, 2017, along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, 2013 in purple, and 2012 in dotted red. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Ice growth during November 2017 averaged 80,100 square kilometers (30,900 square miles) per day. This was stronger than the average rate for the month of 69,600 square kilometers (26,900 square miles) per day. Ice growth was particularly rapid within Hudson Bay, Baffin Bay, and the Kara Sea.

November air temperatures at 925 hPa (about 3,000 feet above sea level) were above average over essentially all of the Arctic Ocean, with prominent warm spots (more than 6 degrees Celsius, or 11 degrees Fahrenheit above the 1981 to 2010 average) over the Chukchi Sea and north of Svalbard. The unusual warmth in the Chukchi Sea at least in part manifests the extensive open water in this region, but a pattern of winds blowing in from the southwest also appears to have had an influence. The warmth north of Svalbard is more clearly related to the average pattern of atmospheric circulation over the month, with an area of low pressure centered over the Norwegian Sea and an area of high pressure centered north of the Taymyr Peninsula combining to transport warm air into the region.

November 2017 compared to previous years

ice extent trend

Figure 3. Monthly November ice extent for 1979 to 2017 shows a decline of 5.14 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

The linear rate of sea ice decline for November is 55,000 square kilometers (21,200 square miles) per year, or 5.14 percent per decade. Recall from our previous post that NSIDC recently revised the way in which monthly average extents are computed, which has minor impacts on computed trends.

Open water in the Chukchi Sea

sea ice concentration

Figure 4. The map at top shows an analysis of sea ice concentration on November 30, 2017 in the area of the Bering and Chukchi Seas. The graph at bottom shows the combined sea ice concentration from 1978 to 2017, based on Sea Ice Index data.

Credit: Rick Thoman of the NOAA National Weather Service Alaska Region
High-resolution image

Based on an analysis by Rick Thoman of the NOAA National Weather Service, as of 19 November, ice extent in the combined Beaufort and Chukchi Seas sector was the lowest ever observed in the sea ice record (Figure 4). This was largely driven by the lack of sea ice within the Chukchi Sea. By the end of November, the Beaufort Sea was completely ice-covered. The NOAA analysis makes use of the NSIDC Sea Ice Index data set. As discussed in our June 7 post, the current state of the ice cover in this region likely has its origin as far back as last year, when warm conditions favored the persistence of open water in the Chukchi Sea into December of 2016.

Strong winds from the north occurred for a few days at the end of March and early April, pushing ice southward in the Bering Sea, breaking up the ice in the Chukchi Sea, and even flushing some ice out through the Bering Strait. We also suggested a possible role of a strong oceanic heat inflow to the Chukchi Sea via Bering Strait. In support of this view, in the summer of 2017, Rebecca Woodgate of the University of Washington, Seattle, sailing on the research vessel Norseman II, recovered mooring data that indicated an early arrival of warm ocean water in the strait, about a month earlier than the average. This resulted in June ocean temperatures that were 3 degrees Celsius (5 degrees Fahrenheit) above average. Higher ocean temperatures in summer plays a large role in the timing of when the ice will form again in winter. There is likely a considerable amount of heat remaining in the top layer of the ocean, which will need to be lost to the atmosphere and outer space before the region becomes fully ice covered.

Low Antarctic sea ice extent

Figure 5a. Antarctic sea ice concentration from AMSR2, in percent, for November 28, 2017. The Maud Rise polynya is seen at top.

Credit: University of Bremen
High-resolution image

Figure 5b. Small tabular icebergs are seen in the marginal ice zone of the northern Weddell Sea on November 22, 2017 during a NASA Operation IceBridge flight.

Credit: NASA/John Sonntag
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In the Southern Hemisphere, where it is late spring, sea ice declined at a faster-than-average pace after the very late-season October 12 maximum extent. This led to the third-lowest November average monthly extent in the satellite record, behind 1986 and 2016. Sea ice extent was near-average in all regions except the Weddell Sea, where extent is at a satellite-era record low.

The atmospheric circulation for November exhibited a very strong wave-3 pattern. In a wave-3 pattern, there are three major low-pressure areas around the continent separated by three high-pressure areas. Air temperatures for the month were near-average in most regions except for the eastern Weddell Sea, consistent with the reduced sea ice extent there.

The Maud Rise Polynya (Figure 5a) continued to grow through November, as increased sunshine and air temperatures allowed the upwelling warm water to expand the opening in the floating sea ice cover. At the beginning of December,  retreat of the sea ice edge converted the polynya to a large embayment in the sea ice cover.

Freezing in the dark

Rapid expansion of the Arctic sea ice cover is the norm for October as solar input dwindles and the remaining heat in the upper ocean is released upwards, warming the lower atmosphere and escaping to space. Because of late season growth, the seasonal Antarctic maximum we previously reported as occurring on September 15 was exceeded, with a new maximum set on October 11 and 12. This is the second-lowest and second-latest seasonal maximum extent in the satellite record.

Overview of conditions

Figure 1. Arctic sea ice extent for October 2017 was6.71 million square kilometers (2.60 million square miles). The magenta line shows the 1981 to 2010 average extent for that month.

Figure 1. Arctic sea ice extent for October 2017 was 6.71 million square kilometers (2.60 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent for October 2017 averaged 6.71 million square kilometers (2.60 million square miles), the fifth lowest in the 1979 to 2017 satellite record. This was 1.64 million square kilometers (633,000 square miles) below the 1981 to 2010 average and 820,000 square kilometers (317,000 square miles) above the record low October extent recorded in 2012. By the end of October, extent remained below average throughout most of the Arctic except within the Laptev Sea, which is fully ice covered. Ice growth over the month was most prominent within the Beaufort, East Siberian, and Laptev Seas and within Baffin Bay. In the Chukchi, Kara, and Barents Seas, the rate of ice growth was slower. Ice extent also remains far below average in the East Greenland Sea.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of November 2, 2017, along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, 2013 in purple, and 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data.

Figure 2a. The graph above shows Arctic sea ice extent as of November 2, 2017 along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, 2013 in purple, and 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Figure 2b. This plot shows Arctic air temperature anomalies at the 925 hPa level in degrees Celsius for October 2017. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Figure 2b. This plot shows Arctic air temperature anomalies at the 925 hPa level in degrees Celsius for October 2017. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Figure 2c. This plot shows Arctic air temperatures as a function of both height and latitudes. Above average air temperatures for the Arctic as a whole extend up to approximately 9,200 meters (30,000 feet) high in the atmosphere. Colors indicate temperatures in degrees Celsius. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Figure 2c. This plot shows Arctic air temperatures as a function of height and latitudes. Above average air temperatures for the Arctic as a whole extend up to approximately 9,200 meters (30,000 feet) altitude. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Ice growth during October 2017 averaged 94,200 square kilometers (36,000 square miles) per day. This was 5,100 square kilometers (2,000 square miles) per day faster than the average rate of ice growth for the month. Total ice extent for the month remains more than 2 standard deviations below the 1981 to 2010 average.

October air temperatures at 925 hPa (about 3,000 feet above sea level) were 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) above average over most of the Arctic Ocean and up to 7 degrees Celsius (13 degrees Fahrenheit) above average over the East Greenland Sea. Unusually high temperatures over the East Greenland Sea appear to largely reflect the transport of warm air from Eurasia, driven by the combination of above average sea level pressure over the Kara and Barents Seas, and below average pressure over the North Atlantic and Greenland. Elsewhere, above average near surface air temperatures reflect in part the exchange of heat from the ocean to the atmosphere as the ocean cools and sea ice forms, such as within the Chukchi Sea. A plot of temperatures as a function of both height and latitudes shows that the above average air temperatures for the Arctic as a whole extend up to approximately 9,200 meters (30,000 feet) high in the atmosphere.

October 2017 compared to previous years

Figure 3. Monthly October ice extent for 1979 to 2017 shows a decline of 9.3 percent per decade.

Figure 3. Monthly October ice extent for 1979 to 2017 shows a decline of 9.3 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

The linear rate of sea ice decline for October is 77,600 square kilometers (30,000 square miles) per year, or 9.3 percent per decade relative to the 1981 to 2010 average. While this appears as an increase in the rate of October ice retreat compared to the trend reported last year, it is not a climate signal but is rather largely a result of using a different averaging method to derive the monthly average sea ice extent values (see below).

Effects of snow salinity on CryoSat-2 ice freeboard estimates

Figure 4. This schematic illustrates how salinity shifts the source of the radar signature in the icepack.

Figure 4. This schematic illustrates how salinity shifts the source of the radar signature in the icepack. Ice thickness can be over-estimated by radar satellites (CryoSat-2) when snow conditions are more saline.

Credit: V. Nandan
High-resolution image

After the end of sea ice melt season, the ocean cools and new sea ice forms. The ice crystals that form expel salt into the water. Some of this salt, or brine, is also expelled upwards to the surface of the ice or into snow that has fallen since the ice formed. The brine is then wicked upwards into the snowpack, leading to a slightly saline snowpack, ranging from 1 to 20 parts per thousand (standard seawater is about 35 parts per thousand). This saline snow is a strong reflector of radar energy.

A recent study led by the Cryosphere Climate Research Group at the University of Calgary investigated the impact of snow salinity on retrieving sea ice thickness from radar altimeters, such as CryoSat-2. The study shows that the snow layers observed over much of the Arctic’s first-year ice are salty enough to reflect the radar pulse from CryoSat-2, a radar altimeter used to measure sea ice thickness and ice sheet elevation. They calculate that a correction factor could compensate for this effect, and improve sea ice thickness measurements. While snow salinity is important, other factors, such as surface roughness and ice density also contribute to uncertainties in ice thickness, and they can potentially cancel each other out. Continued comparisons to observed thickness data is crucial to better quantify these uncertainties.

Antarctica’s double-humped sea ice maximum

Figure 5. This graph shows the first and second peaks in extent during the 2017 Antarctic sea ice freeze up.

Figure 5a. This graph shows the first and second peaks in extent during the 2017 Antarctic sea ice freeze up. The extent line for the year 2002 is also shown and has a similar pattern to 2017. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Figure 5b. This map shows Antarctic sea ice concentration on October 31, 2017. Note the Maud Rise polynya at the top of the image. Data are from the Advanced Microwave Scannig Radiometer 2 (AMSR2)||Credit: Institute of Environmental Physics, University of Bremen|High-resolution image

Figure 5b. This map shows Antarctic sea ice concentration on October 31, 2017. Note the Maud Rise polynya at the top of the image. Data are from the Advanced Microwave Scanning Radiometer 2 (AMSR2).

Credit: Institute of Environmental Physics, University of Bremen
High-resolution image

In our last post, we noted that Antarctic sea ice may have reached its maximum extent for the year on September 15, at 17.98 million square kilometers (6.94 million square miles). However, after two weeks of decline, extent increased again reaching a second and final maximum of 18.03 million square kilometers (6.96 million square miles) on October 11 and 12. This is tied with 2002 for the latest maximum on record and is the second lowest Antarctic maximum extent in the satellite data record, slightly higher than 1986. Interestingly, 2002 had a similar Bactrian maximum pattern.

The Maud Rise polynya (or Weddell Sea polynya) continues to be a significant feature of the sea ice cover near 5°E longitude and 65°S. The feature appeared around September 13 and grew to its approximate current extent by September 17. Its current size remains about 30,000 square kilometers (12,000 square miles).

Winds and ocean temperatures continue to drive Antarctic sea ice variability. Since there is no land boundary to the north of the Antarctic continent, sea ice in the Southern Hemisphere is free to expand toward the equator until it reaches water temperatures that are high enough to melt sea ice. As a result, changes in winds or ocean temperatures can have a large influence on the amount of sea ice year to year. Changes in winds related to the positive phase of the Southern Annular Mode (SAM) appear to explain the positive trend in total Antarctic sea ice extent. When the SAM is in a positive phase during austral summer, stronger than average westerly winds blow around the Antarctic continent, and sea ice is pushed both westward and slightly northward due to the Coriolis effect. In addition, below average sea surface temperatures persist through the summer and lead to increased sea ice growth the following autumn, while the negative phase precedes higher sea surface temperatures and reduced sea ice growth. A new study suggests the negative SAM mode during 2016/2017 austral summer largely explained the record minimum Antarctic sea ice extent observed in March 2017.

Revised computation of the monthly mean extent

Figure 6. This chart compares the monthly October Arctic sea ice extents generated from the old (black dashed line) and the new (solid black line) averaging method.

Figure 6. This chart compares the monthly October Arctic sea ice extents generated from the old (black dashed line) and the new (solid black line) averaging method. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

We have updated the way the monthly average sea ice extent is calculated in the NSIDC Sea Ice Index, the source for our sea ice extent estimates. The monthly average total extent (and area) are now computed as an average of the daily values over the month. Historically, the monthly mean sea ice extent has been calculated based on the monthly mean averaged sea ice concentration field. While there is a rationale for both approaches, the new method is more intuitive and eliminates unusual and unexpected results in months when there is rapid ice growth and retreat. Most of the new monthly mean extents are smaller than the previous values with a mean extent difference between -0.45+0.24 and -0.23+0.16 million square kilometers for the Arctic and Antarctic, respectively. The largest differences for the Arctic occur during the month of October due to the rapid ice growth rates typical at that time of year, with the largest difference of -1.20 million square kilometers in October 2012. Changes in rankings and trends were much smaller because the new method tends to affect all years of a given month in a similar manner. October is also the month with the largest trend difference, increasing in magnitude from -7.4 percent per decade to -9.3 percent per decade. Changes in Arctic trends for other months are much smaller.

Similarly, in the Antarctic, differences in averaging methods results in the largest changes during the month of December when the ice cover is rapidly receding. The largest difference of -1.27 million square kilometers occurs in December 1981. The largest changes in the trends are for January and December with a change in value from +2.7 to +3.5 and +1.2 to +1.9 percent per decade, respectively. For more detailed information on the impacts of the revised averaging methods on trends and rankings, please see NSIDC Special Report 19.

Further reading

Nandan, V., T. Geldsetzer, J. Yackel, M. Mahmud, R. Scharien, S. Howell, J. King, R. Ricker, and B. Else. 2017. Effect of snow salinity on CryoSat-2 Arctic first-year sea ice freeboard measurements: Sea ice brine-snow effect on CryoSat-2. Geophysical Research Lettersdoi:10.1002/2017GL074506.

Doddridge, E. W. and J. Marshall. 2017. Modulation of the seasonal cycle of Antarctic sea ice extent related to the Southern Annular Mode. Geophysical Research Letters, 44, 9761–9768. doi: 10.1002/2017GL074319.

Windnagel, A., M. Brandt, F. Fetterer, and W. Meier. 2017. Sea Ice Index Version 3 Analysis. NSIDC Special Report 19. https://nsidc.org/sites/nsidc.org/files/files/NSIDC-special-report-19.pdf.

Arctic sea ice 2017: Tapping the brakes in September

After setting a record low seasonal maximum in early March, Arctic sea ice extent continued to track low through July. However, the rate of ice loss slowed in August and September. The daily minimum extent, reached on September 13, was the eighth lowest on record, while the monthly average extent was seventh lowest. In Antarctica, sea ice extent may have reached its annual winter maximum.

Overview of conditions

ice extent image

Figure 1. Arctic sea ice extent for September 2017 was 4.87 million square kilometers (1.88 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent for September 2017 averaged 4.87 million square kilometers (1.88 million square miles), the seventh lowest in the 1979 to 2017 satellite record. This was 1.67 million square kilometers (645,000 square miles) below the 1981 to 2010 average, and 1.24 million square kilometers (479,000 square miles) above the record low September set in 2012.

After reaching the minimum on September 13 (eighth lowest on record), extent initially increased slowly (about 20,000 square kilometers, or 8,000 square miles, per day). However, starting September 26 and persisting through the end of the month, ice growth rates increased to about 60,000 square kilometers (23,000 square miles) per day. During the second half of the month, extent increased in all sectors except in the Beaufort Sea, where some local ice retreat persisted. The most rapid growth occurred along the Siberian side of the Arctic Ocean, where the ice edge advanced as much as 150 kilometers (90 miles) over the latter half of September. At the end of September, the ice edge in the Beaufort and Chukchi Seas remained considerably further north than is typical.

Conditions in context

extent timeseries

Figure 2a. The graph above shows Arctic sea ice extent as of October 4, 2017, along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, 2013 in purple, and 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

pressure anomaly

Figure 2b. This image shows the departure from average sea level pressure in millibars over the Arctic for June, July, and August in 2017. Yellows and reds indicate higher than average pressures; blues and purples indicate lower than average pressures.

Credit: NSIDC courtesy NOAA/ESRL Physical Sciences Division
High-resolution image

September air temperatures at the 925 hPa level (approximately 2,500 feet above sea level) were above average over much of the Arctic Ocean. Temperatures ranged from 5 degrees Celsius (9 degrees Fahrenheit) above the 1981 to 2010 long term average in the far northern Atlantic east of Greenland, to 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) above the reference period in the western Arctic. Cooler conditions (1 degree Celsius or 2 degrees Fahrenheit below average) were present in Baffin Bay. Part of the above average temperatures over the coastal areas of the Arctic Ocean and in the northern North Atlantic likely results from heat fluxes from open water.

Looking back at this past summer (June through August), air temperatures at the 925 hPa level averaged for June through August were near or below the 1981 to 2010 average over much of the Arctic Ocean, notably along the Siberian side centered over the Laptev Sea (1 degree Celsius or 1.8 degrees Fahrenheit below the 1981 to 2010 average). By contrast, temperatures were slightly above average over much of the East Siberian, Chukchi and Beaufort Seas (1 degree Celsius, or 1.8 degrees Fahrenheit above average).

Like 2016, the summer of 2017 was characterized by persistently stormy patterns over the central Arctic Ocean, reflected in the summer average sea level pressure field (Figure 2b) as an area of low pressure centered just south of the North Pole in the Siberian sector of the Arctic. As has been shown in past studies, low pressure systems found over the central Arctic Ocean in summer are typically “cold cored.” This helps to explain the cool summer temperatures noted above. The cyclonic (counterclockwise) winds associated with the stormy pattern also tend to spread out the sea ice. Both processes likely helped to slow sea ice loss this summer.

September 2017 compared to previous years

ice trend

Figure 3. Monthly September ice extent for 1979 to 2017 shows a decline of 13.2 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

The linear rate of sea ice decline for September is 86,100 square kilometers (33,200 square miles) per year, or 13.2 percent per decade relative to the 1981 to 2010 average. For comparison, the decline rate was calculated at 13.7 percent after the 2013 minimum, and 13.4 percent in 2016. Although sea ice shows significant year-to-year variability, the overall trend of decline remains strong.

Thickness and age trends in Arctic sea ice from models and data

Figure 4a. This image from the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) shows Arctic sea ice thickness departures from average (anomaly) in meters for September 2017, relative to the 2000 to 2015 average. Reds indicate thicker than average ice; blues indicate thinner than average ice.

Credit: NSIDC courtesy University of Washington Polar Science Center
High-resolution image

ice age

Figure 4b. Sea ice age distribution at the annual minimum extent for 1985 (upper left) and 2017 (upper right). Time series (bottom) of different age categories the minimum extent for 1985 to 2017. Note that the ice age product does not include ice in the Canadian Archipelago. Data from Tschudi et al., EASE-Grid Sea Ice Age, Version 3

Credit: W. Meier/National Snow and Ice Data Center, M. Tschudi et al.
High-resolution image

According to estimates from the University of Washington Polar Science Center’s PIOMAS, which assimilates observational data into a coupled ice-ocean model, sea ice volume was at record low levels from January through June of 2017. However, the generally cool summer conditions slowed the rate of ice melt, and the ice volume for September ended up fourth lowest in the PIOMAS record, above 2010, 2011, and 2012.

Another way to assess the volume of the ice, at least in a qualitative sense, is through tracking sea ice age (Figure 4b). Older ice is generally thicker ice. Over the satellite record, there has been a significant decline in coverage of the oldest, thickest ice. While this year’s minimum sea ice extent is higher than in 2016, the marginal gain can be largely attributed to younger ice types: first-year ice (0 to 1 years old) and second-year ice (1 to 2 years old). The oldest ice, that which is over 4 years old, is only slightly higher than last year and remains almost non-existent within the Arctic. At the minimum this year, ice older than 4 years constituted only ~150,000 square kilometers (~58,000 square miles), compared to over 2 million square kilometers (~770,000 square miles) during the mid-1980s.

Antarctic maximum extent

antarctic sea ice

Figure 5. The graph above shows Antarctic sea ice extent as of October 4, 2017, along with daily ice extent data for 2017 (aqua), 2016 (red), 2013 (dotted green), and 1986 (yellow). The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Antarctic sea ice may have reached its maximum extent on September 15, at 17.98 million square kilometers (6.94 million square miles), among the earliest maxima on record. If this date and extent hold, it will be the second-lowest daily maximum in the satellite record, 20,000 square kilometers (7,700 square miles) above 1986. Antarctic sea ice extent has been at record or near-record lows since September 2016. A series of recent studies have explored causes of the sudden decline in extent that occurred in austral late winter and spring of 2016. Most studies conclude that an unusual period of strong meridional winds—consistent with a very pronounced negative phase of the Southern Annular Mode index, coupled with a significant ‘wave-3 pattern’ in the atmospheric circulation—were the cause. A ‘wave-3 pattern’ refers to a tendency for circulation around the southern continent to resemble a three-leaf clover, rather than the more typical near-zonal (along lines of latitude) pattern.

The Maud Rise polynya, discussed in our last post, continues to grow and is now at about 35,000 square kilometers (14,000 square miles). A recent study (see Further reading, below) discusses how its formation is related to climate patterns and natural variability, and that the recent reappearance supports a forecast by an updated climate model.

Driftwood and long-term changes in Arctic ice movement

circulation

Figure 6. The maps show two modes of wintertime Arctic sea ice circulation patterns. (a) shows the Low Arctic Oscillation (AO) index has a strong Beaufort Gyre which supports ice re-circulation within the Arctic. (b) shows the High AO index in which the Beaufort Gyre is weak and the Transpolar Drift expands, leading to Arctic ice exported in a shorter time interval. Bold numbers show the average time in years for ice starting from various locations to be exported through Fram Strait under the illustrated patterns. The red dashed lines encircle the region of ice recirculation and persistence (Rigor et al., 2002). Over continents, light blue lines show watersheds with named major rivers (shown as bold blue lines) that export driftwood into the Arctic Ocean. Green letters indicate driftwood sample regions: CAA, Canadian Arctic Archipelago; EG, East Greenland; JM, Jan Mayen; NG, North Greenland; FJL, Franz Josef Land; NZ, Novaya Zemlya; SB, Svalbard. Circulation patterns compiled and modified from Rigor et al. (2002).

Credit: G. Hole and M. Macias-Fauria, The Cryosphere Discuss.
High-resolution image

While the satellite record has been key in documenting large declines in the Arctic sea ice cover during the past four decades, the data record is still relatively short. To provide a longer record, scientists turn to the geologic record and proxy data. One approach is to analyze the age, transport, and deposition of driftwood. Driftwood distribution depends strongly on past sea ice conditions and ocean currents. New research using 913 driftwood samples collected across the western Arctic (Figure 6) has shed new insight on sea ice changes during the Holocene, between 12,000 years ago to present. During the early Holocene (12,000 to 8,000 years ago), the analysis suggests that the clockwise Beaufort Gyre dominated Arctic Ocean circulation, allowing more sea ice to stay within the Arctic Ocean. In the mid-Holocene (8,000 to 4,000 years ago), temperatures were higher and the Transpolar Drift dominated, leading to more ice export out of the Arctic Ocean through Fram Strait and less sea ice in the Arctic Ocean. In the late Holocene (4,000 years ago to present), the Beaufort Gyre once again strengthened as temperatures slowly cooled until the most recent several decades.

Further reading

Hole, G. M. and M. Macias-Fauria. 2017. Out of the woods: Driftwood insights into Holocene pan-Arctic sea ice dynamic., J. Geophys. Res. Oceans, 122, doi:10.1002/2017JC013126.

Reintges, A., T. Martin, M. Latif, and W. Park. 2017. Physical controls of Southern Ocean deep-convection variability in CMIP5 models and the Kiel Climate Model. Geophys. Res. Lett., 44 (13), 6951-6958, doi:10.1002/2017GL074087.

Rigor, I.G., Wallace, J.M. and Colony, R.L. 2002. Response of sea ice to the Arctic Oscillation. Journal of Climate,15 (18), 2648-2663, doi:10.1175/1520-0442(2002)015<2648:ROSITT>2.0.CO;2.

Schlosser, E., Haumann, F. A., and Raphael, M. N. Atmospheric influences on the anomalous 2016 Antarctic sea ice decay. The Cryosphere Discuss., doi:10.5194/tc-2017-192, in review, 2017.

Arctic sea ice at minimum extent

On September 13, Arctic sea ice appears to have reached its seasonal minimum extent of 4.64 million square kilometers (1.79 million square miles), the eighth lowest in the 38-year satellite record. The overall rate of ice loss this summer was slowed by a persistent pattern of low sea level pressure focused over the central Arctic Ocean.

Please note that this is a preliminary announcement. Changing winds or late-season melt could still reduce the Arctic ice extent, as happened in 2005 and 2010. NSIDC scientists will release a full analysis of the Arctic melt season, and discuss the Antarctic winter sea ice growth, in early October.

Overview of conditions

Figure 1. Arctic sea ice extent for September 13, 2017 was 4.64 million square kilometers (1.79 million square miles), the eighth lowest in the satellite record. The orange line shows the 1981 to 2010 average extent for that day.

Figure 1. Arctic sea ice extent for September 13, 2017 was 4.64 million square kilometers (1.79 million square miles), the eighth lowest in the satellite record. The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

On September 13, 2017, sea ice extent reached an annual minimum of 4.64 million square kilometers (1.79 million square miles). This was 1.58 million square kilometers (610,000 square miles) below the 1981 to 2010 median extent for the same day, and 1.25 million square kilometers (483,000 square miles) and 500,000 square kilometers (193,000 square miles) above the 2012 and 2016 extents for the same day, respectively.

During the first two weeks of September, the ice edge continued to retreat in the Chukchi, East Siberian, and Kara Seas, whereas it slightly expanded in the Beaufort and Laptev Seas. The ice edge remains far to the north of its average position in the Chukchi Sea. The Northern Sea Route is largely open; Amundsen’s Northwest Passage (the southern route) has up to 50 percent ice cover in some places, though as noted in our last post, ships have successfully navigated through the southern route with icebreaker assistance. The northern Northwest Passage route, entered from the west via McClure Strait, remains choked by consolidated, thick, multi-year ice.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of September 17, 2017, along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, 2013 in purple, and 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.||Credit: National Snow and Ice Data Center|High-resolution image

Figure 2a. The graph above shows Arctic sea ice extent as of September 17, 2017, along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, 2013 in purple, and 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Figure 2b. This image shows average sea level pressure over the Arctic Ocean for the period of September 1 to 16, 2017.

Figure 2b. This image shows average sea level pressure over the Arctic Ocean for the period of September 1 to 16, 2017.

Credit: NSIDC courtesy NOAA/ESRL Physical Sciences Division
High-resolution image

The date of the minimum ice extent for 2017 was two days earlier than the average minimum date of September 15. The earliest annual sea ice minimum in the satellite record occurred on September 5 in the years 1980 and 1987, and the latest on September 23, 1997.

As is typical of this time of year when the solar radiation received at the surface is quickly waning, the rate of ice loss slowed during the first half of September. Ice retreat from the beginning of September until the minimum averaged 25,300 square kilometers (9,770 square miles) per day, slightly faster than the 1981 to 2010 average for the same period of 22,800 square kilometers (8,800 square miles) per day.

The pattern of low sea level pressure over the central Arctic Ocean that persisted through this summer and inhibited summer ice loss has broken down. For the first half of September, the pattern has instead been one of above-average sea level pressure centered over the Barents Sea and extending across part of the Arctic Ocean (Figure 2b). Corresponding air temperatures at the 925 hPa level (about 2,500 feet above sea level) were above average over most of the Arctic Ocean. Above average temperatures over some parts of the Arctic Ocean likely reflect heat transfer to the atmosphere from areas of open water, hence cooling the ocean.

Ten lowest minimum Arctic sea ice extents (satellite record, 1979 to present)

Table 1.  Ten lowest minimum Arctic sea ice extents (satellite record, 1979 to present)
 RANK  YEAR MINIMUM ICE EXTENT DATE
IN MILLIONS OF SQUARE KILOMETERS IN MILLIONS OF SQUARE MILES
1 2012 3.39 1.31 Sept. 17
2 2016
2007
4.14
4.15
1.60
1.60
Sept. 10
Sept. 18
4 2011 4.34 1.67 Sept. 11
5 2015 4.43 1.71 Sept. 9
6 2008 4.59 1.77 Sept. 19
7 2010 4.62 1.78 Sept. 21
8 2017 4.64 1.79 Sept. 13
9 2014 5.03 1.94 Sept. 17
10 2013 5.05 1.94 Sept. 13

Effects of seasonal ice retreat in the Beaufort and Chukchi Seas

Figure 3. This chart shows combined sea ice extent in the Chukchi and Beaufort Seas from August 15 to October 7 for the years 2006 to 2016, including the extent so far for 2017. The colored dots show the day the minimum occurred in the region during a specific year. ||Credit: Courtesy R. Thoman/National Weather Service Alaska Region Environmental and Scientific Services Division| High-resolution image

Figure 3. This chart shows combined sea ice extent in the Chukchi and Beaufort Seas from August 15 to October 7 for the years 2006 to 2016, including the extent so far for 2017. The colored dots show the day the minimum occurred in the region during a specific year. Data are from the Multisensor Analyzed Sea Ice Extent (MASIE) product.

Credit: Courtesy R. Thoman/National Weather Service Alaska Region Environmental and Scientific Services Division
High-resolution image

According to a report by the Alaska Dispatch News, the lack of sea ice forced walruses to the shore of Alaska’s Chukchi Sea earlier than any time on record. The lack of ice also forced biologists monitoring Alaska polar bears to cut short their spring field season. In turn, the NOAA National Weather Service Climate Prediction Center states that because of the extensive open water, air temperatures over the Beaufort and Chukchi Seas and along the North Slope of Alaska will likely be far above average through this autumn.

Rick Thoman of the National Weather Service in Fairbanks, Alaska compiled an analysis of the combined Chukchi and Beaufort Seas ice extent from the Multisensor Analyzed Sea Ice Extent (MASIE) product. MASIE is based on operational ice analyses at the U.S. National Ice Center and is archived and distributed by NSIDC. It shows that 2017 tracked near record lows for the region through much of the summer, but after mid-August the pace of ice loss slowed relative to recent years. While it appears unlikely that extent in the Beaufort and Chukchi Seas will reach a record low (set in 2012), it will still be among the four or five lowest in the MASIE record (Figure 3). Note that the range in dates for the minimum extent in the region differs from those for the Arctic as a whole and tend to be later, ranging from September 10 in 2015 to September 25 in 2007 and 2008. In other words, the Chukchi and Beaufort Seas may continue to lose ice even after the overall Arctic minimum extent is reached. From the passive microwave data (not shown), the Chukchi/Beaufort minimum has occurred as early as August 14 in 1980 to as late as October 2 in 1991.

Antarctic sea ice approaching winter maximum

Figure 4a. The graph above shows Antarctic sea ice extent as of September 17, 2017, along with daily ice extent data for four previous years.

Figure 4a. The graph above shows Antarctic sea ice extent as of September 17, 2017, along with daily ice extent data for four previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in dashed brown, 2013 in purple. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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Figure 4b: This map shows Antarctic sea ice concentration on September 16, 2017. Note the Maud Rise polynya at the top of the image. Data are from the Advanced Microwave Scannig Radiometer 2 (AMSR2).

Figure 4b: This map shows Antarctic sea ice concentration on September 16, 2017. Note the Maud Rise polynya at the top of the image. Data are from the Advanced Microwave Scannig Radiometer 2 (AMSR2).

Credit: G. Heygster, C. Melsheimer, J. Notholt/Institute of Environmental Physics, University of Bremen
High-resolution image

Following the record low summer minimum extent in March, Antarctic sea ice extent is now nearing its winter maximum. This will likely be among the five lowest winter extents in the satellite era. As of mid-September, Antarctic ice extent was just under 18 million square kilometers (7 million square miles), which is approximately half a million square kilometers below the 1981 to 2010 median ice extent. Sea ice is below the typical extent in the Indian Ocean sector, the northern Ross Sea, and the northern Weddell Sea, and slightly above average extent in the northern Amundsen Sea region.

Between September 9 and September 17 of 2016, Antarctic sea ice lost nearly 100,000 square kilometers (38,600 square miles) of sea ice per day, and sea ice extent moved from near-average to a near-record-daily low by September 17. For the next 12 months Antarctic sea ice remained extremely low. Record low ice extents were set every day from November 5, 2016 to April 10, 2017. Extents averaged for November and December of 2016 were five standard deviations below average. No other 12-month period (September 2016 to August 2017) has had such persistently low sea ice extent. The year 1986 had near-record low extent for the winter period (June to December), but there were periods of near-average and even above-average ice extent earlier in the calendar year.

Beginning around September 2, an opening in the Antarctic sea ice pack formed north of Dronning Maud Land in the easternmost Weddell Sea (near 64°S, 5°E). By mid-September, this opening, or polynya, had grown to about 12,000 square kilometers (4,600 square miles). This feature has been observed intermittently in the Antarctic pack ice since the first satellite data became available in the 1970s. In 1974, 1975, and 1976, the polynya was much larger, averaging 250,000 square kilometers (96,500 square miles). It was absent for many years in the 1980s and 1990s. In recent years the feature has been observed sporadically and has been much smaller.

The polynya is formed when ocean currents uplift deep warm ocean water to the surface where it melts the sea ice. An oceanic plateau called the Maud Rise is responsible for forcing the vertical movement of the water. The persistence of certain atmospheric patterns, such as the southern annular mode, or SAM, is thought to play a role in driving the deep water layer against the Maud Rise.

2017 Arctic sea ice minimum animation

See the NASA animation of Arctic sea ice extent from the beginning of the melt season on March 8, 2017 to the day of the annual minimum on September 13, 2017 here.

Further reading

Gordon, A.L., Visbeck, M. and Comiso, J.C. 2007. A possible link between the Weddell Polynya and the Southern Annular Mode. Journal of Climate20(11), 2558-2571. doi:10.1175/JCLI4046.1

Holland, D.M. 2001. Explaining the Weddell Polynya–a large ocean eddy shed at Maud Rise. Science, 292(5522), 1697-1700. doi:10.1126/science.1059322.

Erratum

In Table 1, years 2014 and 2013 were both ranked ninth lowest. They should have been ninth and tenth respectively. This has been corrected.