Arctic sea ice observations until the end of July 2013

5th August, 2013

DMI, Center for Ocean and Ice
Section for Polar Oceanography

Figur 7. The total ice-covered area in the Arctic for the years 2009 to June 2013.

The low sea ice export through Fram Strait, the relatively normal spring temperatures and the late beginning of the melt season in the Arctic Ocean, has led to a general larger sea ice extent than the past 5-8 years, since the sea ice extent peak in March (figure 7). Despite a larger sea ice extent in June and July than in previous years, the ice loss through melting during the first 2 weeks of July was very high, with a daily melt rate of approximately 120.000km2, i.e. an area comparable to three times that of Denmark. After that, the sea ice loss by melting apparently stopped.

Figure 6. The mean Arctic temperature north of 80° N.

The minimum Arctic sea ice extent in September is largely affected by three conditions: 

1) the ice thickness in the early spring, 2) the beginning of the melt season, and 3) the weather during spring and summer. As the Arctic sea ice gets thinner, the minimum extent in September is becoming more controlled by weather conditions during summer. Consequently, the minimum extent is increasingly difficult to predict, and the year to year variability is larger than previous.

This year, the melt season in the Arctic Ocean began 2 weeks later than normal for the period 1958 until today, and the Arctic temperatures have generally been close to the climatological mean temperatures in spring (figure 6). Because of this, the sea ice has had more time to grow and less time to melt. The wind conditions in the Arctic Ocean have been dominated by a low pressure system over the central regions in June, and a relative high pressure in July. The (mainly) wind-driven transpolar drift from Siberia towards Greenland and Fram Strait has for that reason been weak during large part of this spring and summer and the loss of sea ice through Fram Strait has been low. 

Figure 8. Average Arctic sea ice thickness over the ice-covered regions from PIOMAS for a selection of years. From Polar Science Center.

The large variability in July melt-rates indicates that the ice extent has been controlled by local weather. The large weather-influence on the melt-rate is occurring because the sea ice has become thin and fragile. At the Polar Science Centre at The University of Washington, they estimate (from modeling results) that the average sea ice thickness in 2011-2013 is significantly thinner than in previous years (figure 8). The weather in August will be of crucial importance whether the Arctic faces a new season of record low sea ice extent, or whether the sea ice will recover after last year’s minimum.