Antarctic sea ice appears to have reached its annual maximum extent on October 6. The maximum occurred relatively late compared to past years. In contrast to the past three years, the 2015 maximum did not set a new record high for the period of satellite observations, but was nevertheless slightly above the 1981 to 2010 average.
Overview of conditions
Antarctic sea ice extent reached its likely maximum for the year, at 18.83 million square kilometers (7.24 million square miles) on October 6, 2015. This year’s maximum was the sixteenth highest in the 35-year record. It was 120,000 square kilometers (46,000 square miles) above the average maximum daily extent computed over the 1981 to 2010 period of 18.71 million square kilometers (7.19 million square miles), and 1.33 million square kilometers (514,000 square miles) below the record maximum set in 2014. The date of the maximum was quite late in comparison to the 35-year satellite record. Only one year, 2002, has had a later maximum (October 12).
At the date of the 2015 maximum, Antarctic sea ice extent was greater than average in the Antarctic Peninsula region, the Weddell Sea, and the Wilkes Land coast area; and below average in the Ross Sea and Indian Ocean sectors.
Conditions in context
As recently as July 12, Antarctic sea ice extent was at a record daily high extent for the satellite period of observations. For much of early 2015, Antarctic sea ice extent was either slightly above or slightly below the levels seen on the same date in 2014, the record high year. However, beginning in mid-July, the growth rate for Antarctic sea ice slowed significantly, causing the 2015 maximum extent to be only the sixteenth highest in the record.
It is likely that this slowing of late-winter ice growth is related in part to the build-up of the El Niño conditions. El Niño occurs when a large area of the surface waters in the tropical eastern Pacific Ocean warms, and it has widespread effects on weather patterns. In the Southern Ocean, El Niño conditions are typically associated with a weakening of the Amundsen Sea Low, a persistent region of low air pressure in the southernmost Pacific sector of the Antarctic coast (Raphael et al., 2015). Air pressure in the Amundsen Sea region for the months of August and September was higher than average, indicating a weakening of the low-pressure tendency in the region. Higher-than-average air pressure was also observed in the Indian Ocean sector. These regions saw reduced sea ice growth and even local sea ice retreat as the austral winter progressed, and areas of higher-than-average temperatures near the ice edge.
Patterns of sea ice concentration around Antarctica (the deviation from average ice concentration) for El Niño years show a similar pattern, with more ice near the Peninsula.
Raphael, M. N., G. J. Marshall, J. Turner, R. Fogt, D. Schneider, D. A. Dixon, J. S. Hosking, J. M. Jones, and W. R. Hobbs. 2015. The Amundsen Sea Low: Variability, change and impact on Antarctic climate. Bulletin of the American Meteorological Society 2015, doi:10.1175/BAMS-D-14-00018.1.