Field Notes: The Polar Field Services Newsletter

Arctic Sea Ice Analysis

Arctic sea ice extent for September 2010 was 4.90 million square kilometers (1.89 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. All infographics: NSIDC.

The National Snow and Ice Data Center (NSIDC) in Boulder, Colorado recently announced that the sea ice of the Arctic Ocean region had reached its annual minimum, which is the lowest extent after melting all summer before the ice begins thickening and rebuilding for fall and winter. This year the amount of ice at the end of the summer was the third lowest on record—1.84 square miles (4.76 million square kilometers).

About a week later, the center updated its report to say that the ice had continued to melt (after appearing to begin its winter recovery). In total, scientists estimate there remained 1.78 million square miles of ice following the 2010 summer.

The graph above shows daily Arctic sea ice extent as of October 3, 2010, along with daily ice extents for years wtih the previous four lowest minimum extents. The solid light blue line indicates 2010; dark blue shows 2009, purple shows 2008; dashed green shows 2007; light green shows 2005; and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data.

September 2010 compared to past years

Monthly September ice extent for 1979 to 2010 shows a decline of 11.5% per decade.

Ice extent for September 2010 was the third lowest in the satellite record for the month, behind 2007 (lowest) and 2008 (second lowest). The linear rate of decline of September ice extent over the period 1979 to 2010 is now 81,400 square kilometers (31,400 square miles) per year, or 11.5% per decade relative to the 1979 to 2000 average. Sea ice extent at the end of the melt season is shaped by conditions in the atmosphere and ocean, as well as the condition of the ice cover itself.

Remaining Ice Is Young

The remaining ice in the Arctic is younger and therefore thinner than the ice generally is at this time, according to a more in-depth analysis from NSIDC. In short, in addition to decreasing in area, the ice is also diminishing in volume. Older ice tends to be thicker than younger, one- or two-year-old ice.

This is significant because thinner ice is more susceptible to environmental changes, according to the analysis. Should next summer be as warm as this summer, the level of melt could be great.

Last winter, the wind patterns associated with the negative phase of the Arctic Oscillation transported a great deal of multiyear ice from the coast of the Canadian Arctic into the Beaufort and Chukchi seas. Scientists speculated that much of this ice, some five years or older, would survive the summer melt period. Instead, it mostly melted away.

At the end of the summer 2010, less than 15 percent of the ice remaining the Arctic was more than two years old, compared to 50 to 60 percent during the 1980s. There is virtually none of the oldest (at least five years old) ice remaining in the Arctic (less than 60,000 square kilometers, or 23,000 square miles, compared to 2 million square kilometers, or 722,000 square miles, during the 1980s).

Whether younger multiyear ice (two or three years old) in the Arctic Ocean will continue to age and thicken depends on how much of that ice stays in the Arctic instead of exiting into the North Atlantic through Fram Strait  whether the ice survives its transit across the Beaufort and Chukchi Seas or instead melts away.

Steady Decline

Since NSIDC began satellite measurements of sea ice extent, the trend in the Arctic has been one of decline. Click on this video Arctic Sea Ice Decline to watch a movie of annual maximums and minimums.

For the first 12 years, sea ice melt was usually followed by a recovery. But in 2002 the sea ice minimum fell to a then-record 2.3 million square miles, more than 66,000 square miles below the previous low. It failed to rebound in 2004. In 2005, sea ice extent fell to another low, 2.15 million square miles, and then, in 2007, it underwent a massive drop, to 1.65 million square miles, the lowest yet.

Significance of Arctic Sea Ice Melt Being Studied

Many of the scientists Polar Field Services supports study the direct and indirect consequences of sea ice melting. Please check back frequently for updates on their research. —Rachel Walker

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