Sea Ice Age by Month: More Information

The maps and bar graphs show the age of Arctic sea ice for each year of a chosen month. On the maps, ice that has survived four years or more appears in the darkest shade of blue, while sea ice that is under a year old appears in the lightest shade of green. This time series of maps by month helps show how the amount and location of each type of ice during a particular month has changed from year to year.

The bar graphs show sea ice age as either millions of square kilometers or as a percentage of the total sea ice extent. On the graphs, ice is broken out into three categories to give a closer look at ice age. The bar graphs help show how the proportion of each type of ice has changed during the same time of year, over the satellite record.

This sample images show sea ice for March 2012This sample image shows sea ice age for March 2012.

For sea ice, age matters. Sea ice in the Arctic is becoming younger and thinner, so that the ice pack is even more vulnerable to melting. Young, thin ice can melt very rapidly during a warm Arctic summer. Weather conditions in a particular year can spell the difference between a lower than normal ice extent and a record low ice extent, but the continued thinning of the ice pack means it will not fully recover during the winter regardless of summer conditions.

If ice survives a melt season, it grows thicker over the winter. The next melt season, it is more resistant to melting out. If ice completely melts away during a melt season, the ice cover that re-freezes over winter is much thinner and more vulnerable to melting out the next season. The maps show how over time, more and more older ice is melting out or drifting out of the Arctic and melting, leaving the Arctic covered in a much thinner layer of ice and rendering it even more vulnerable to melt as the proportion of first-year ice increases. This is most noticeable in September, towards the end of the summer melt season, when the bar graphs show a greater area of the Arctic covered in first-year ice.

Both maps show a noticeable decline in multi-year ice since 1985, especially in the last ten years. The largest declines are in the oldest ice. First-year ice tends to be more variable from year to year but overall first-year ice in the ice pack is increasing. In other words, multi-year ice is effectively being replaced by first-year ice, thus thinning the ice pack.

Older ice is hardier. It tends to be thicker, rougher, and more resilient to changes within the atmosphere and ocean, as compared to younger ice. Younger ice tends to be thinner and smoother, and more likely to melt completely for given summer conditions. Thinner ice also more easily drifts with winds and currents, resulting in more openings (leads) in the ice. These openings absorb more sunlight, further increasing melt rates.

The effect of summer melt is different for thinner ice. In the springtime, first-year ice and older ice are both snow covered and reflect sunlight in much the same way. However, once melting begins things become more complicated. As snow melts, water pools in depressions on the surface of the ice. Due to its rough surface, multi-year ice develops deeps depressions. Here, “melt ponds” grow and deepen over a smaller area but for first-year ice the area of melt ponds is much larger. Since first-year ice has a smoother surface, water pools in shallow and widely spread out ponds. Melt ponds are a critical component of melting. These pools of water absorb more solar radiation than the ice surface; they heat up faster. Thus a younger, thinner ice covered with widely spread out melt ponds absorbs more energy in the summer, enhancing melt further.

Satellite data and drifting buoys observe the formation, movements, and disappearance of sea ice. Years of accumulated observations have been used to estimate ice age since the early 1980s. The satellite data and drifting buoy information is used to derive vector fields on a 12.5 by 12.5 kilometer Equal-Area Scalable Earth Grid (EASE-Grid).

Ice age is estimated from the gridded vector fields by tracking the motion of parcels (pixels) of ice over time using the derived vectors. A grid cell must contain at least 15% ice concentration to be mapped. When a grid survives the melt season, the particle ages one year. Since the sea ice minimum for the Arctic happens toward the end of summer (early to mid September), the week following the record low marks the birthday of any ice left over. Weekly data has been averaged to create monthly fields for both the maps and bar graphs.

Some regions of purely seasonal ice have not been mapped. Thus the cited values for ice coverage are less than the actual amount of ice present in the Arctic.


Tschudi, M., Fowler, C., Maslanik, J., Dept. of Aerospace Engr., University of Colorado Boulder


Maslanik, J., J. Stroeve, C. Fowler, and W. Emery. 2011. Distribution and trends in Arctic sea ice age through spring 2011. Geophys. Res. Lett. 38, L13502, doi:10.1029/2011GL047735.

Tschudi, M.A., Fowler, C, Maslanik, J.A., Stroeve, J. 2010. Tracking the movement and changing surface characteristics of Arctic sea ice. IEEE J. Selected Topics in Earth Obs. And Rem. Sens., 10.1109/JSTARS.2010.2048305.

Maslanik, J.A., C. Fowler, J. Stroeve, S. Drobot, J. Zwally, D. Yi and W. Emery, 2007.  A younger, thinner Arctic ice cover:  Increased potential for rapid, extensive sea-ice loss Geophys. Res. Lett. 34, L24501, doi:10.1029/2007GL032043.

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