Sea Ice and Freshwater Ice Assessments
2015/2016 Sea Ice
A. Letterly, J. Key, R. Thoman, and R. Heim
[7 September 2016]
Updated 13 November, 24 November, and 1 December 2016
Arctic Sea Ice
For the second year in a row, Arctic sea ice extent reached a record low wintertime maximum (Figure 1). In March, sea ice extent of 5.607 million square miles (14.522 million square kilometers) edged out the previous winter’s (2014/2015) lowest maximum record by only 3,000 square miles (7770 square kilometers). Though the differences in maximum extents were small, this record was set a month later than last year. The 2016 maximum extent was reached on March 24. While peak ice extent is typically reached by mid-March, the 2015 record was set on February 25. The maximum March 2016 extent was 433,000 square miles (1.121 million square kilometers) below the recent winter maximum average of 6.04 million square miles (15.64 million square kilometers). This is the smallest wintertime ice extent since the beginning of the satellite record in 1979. The September 2015 sea ice minimum that preceded the record-setting winter was also below average, the fourth-lowest minimum extent ever recorded.
Fig. 1. NASA video showing 2015/2016 sea ice extent. Credit: NASA Goddard’s Scientific Visualization Studio.
Ice extent in the spring and early summer of 2016 was below average in the Kara and Barents Seas. Prevailing atmospheric conditions promoted wind-driven divergence in the Beaufort Sea through May, leading to open water and large ice floes off the northern coast of Alaska. Stormy weather associated with low pressure systems tracking from Eurasia to the Central Arctic typically slows the rate of ice thickness decreases, but this year was offset by higher temperatures in coastal Arctic regions. By early August, ice extent in the Alaskan and Siberian Arctic was near average. Achieving a new record low September ice extent is considered by the National Snow and Ice Data Center (NSIDC) to be unlikely. Figure 2 shows that Arctic sea ice extent has been approximately two standard deviations below normal since mid-June, but remains far from the record minimum set in September, 2012.
Fig. 2. Spring and Summer sea ice in the Arctic through 14 August 2016 compared to previous winters. Credit: National Snow and Ice Data Center (NSIDC).
Late August and early September 2016 saw large reductions in ice thickness for much of the central and Siberian Arctic. Figure 3 shows an Arctic-wide reduction in ice extent and ice thickness, leaving open water on all Arctic coastlines except for Greenland and the Canadian Archipelago. Thicker, multi-year ice in the northern Beaufort Sea that persisted through much of the melt period was replaced by open water by September. A large region of open water also extended northward from the East Siberian Sea, forming a peninsula of multi-year ice spanning from the Chukchi Sea to the Central Arctic.
Fig. 3. Ice thickness on August 1 (left) and September 1 (right), 2016 estimated from AVHRR satellite data (Wang et al., 2016). Note the different color scales. The approach used has an upper limit of 2-3 m, particularly during the summer months, so ice thickness along the Canadian Archipelago may be underestimated. Credit: Cooperative Institute for Meteorological Satellite Studies (CIMSS).
Record Minimum October Arctic Sea Ice Extent
(This section was added in November 2016)
While Arctic sea ice extent was low in late summer 2016, it was not a record low. However, October did set a new record minimum ice extent for the satellite era. This is illustrated in Figure 4, which shows the 2016 ice extent, recent record minima, and decadal averages for the 1980's, 1990's, and 2000's. Figure 5 shows the above average temperatures for September and October 2016 over the area poleward of 70N latitude. Figure 6 shows a time series of surface air temperature in October at Barrow, Alaska. The large warming in 2016 is evident, as is the significant reduction in ice extent in the Chukchi and Beaufort Seas (Figure 6, right).
Fig. 4. Arctic sea ice extent for recent years and decadal averages from JAXA-NiPR (left) and NSIDC (right). Note the record low October 2016 ice extent in both datasets. Credit: JAXA-NiPR and NSIDC.
Fig. 5. Left: 2016 surface temperatures over the Arctic (70-90N) compared to recent climatology. Right: Time series of October Arctic surface temperature over the area 70-90N. Both figures are derived from the AVHRR Polar Pathfinder-Extended (APP-x) dataset. Credit: Cooperative Institute for Meteorological Satellite Studies (CIMSS).
Fig. 6. Left: Time series of October surface temperature at Barrow, Alaska. Right: Ice extent in the Chukchi and Beauforts Seas on October 31 in each of the years over the last decade. Credit: R. Thoman (NOAA/NWS Alaska) and the National Snow and Ice Data Center.
Autumn Sea Ice Near Alaska Was Exceptionally Low
(This section was added 1 December 2016 by R. Thoman and R. Heim)
Sea ice coverage near Alaska during the summer of 2016 was something of a mixed bag. Beaufort Sea ice coverage was at near record low values since spring, and waters were navigable for most vessels after mid-July. In the Chukchi Sea waters near Alaska, most sea ice cleared south of 70N by mid-July, and a narrow sea ice free pathway cleared of sea ice along the coast from Wainwright to Point Barrow in late July. However, significant ice persisted off the northwest Alaska coast all summer near the Hanna Shoal region, partially consisting of remnant multi-year sea ice which shifted down from the north during spring storms. While there were occasional shifts of ice to the coast, navigation around Point Barrow was mostly open after early August. During the late summer multiple recreational and tourism vessels, including the large cruise ship “Crystal Serenity” navigated the Chukchi Sea and Beaufort Sea waters without incident. As summer yielded to autumn, sea ice extent near Alaska continued to decrease, as seen in the high resolution analyses from the NOAA National Weather Service (NWS) Alaska Sea Ice Program (Figure 7). Remarkably, the lowest sea ice coverage within 150 nm of the 2016 melt season of Alaska did not occur until approximately October 11.
Fig. 7. Daily sea ice analyses for 2 September (left), 30 September (middle), and 17 October (right) 2016 from the NOAA/NWS Alaska Sea Ice Program (ASIP). Additional analyses are available on the ASIP website.
By the end of October some near-shore ice had formed east of Point Barrow but otherwise the Alaska portion of the Beaufort Sea was ice free south of 73N, and the Chukchi Sea south of 73N was almost completely ice free. Daily ice extent areas derived from the U.S. National Ice Center analyses showed that at the end of October the combined ice extent for the Beaufort and Chukchi Seas was 15 to 20% lower than on the same date in either of the other very low ice extent autumns of 2007 and 2012. The contrast between this autumn (2016) and 2015 was dramatic, as seen in the October 31 comparison shown in Figure 8.
Fig. 8. ASIP sea ice analyses for 31 October 2015 (left) and 31 October 2016 (right).
November sea ice coverage has continued to increase. The Beaufort Sea became effectively ice covered around November 19, about a week later than 2012 (though earlier than in 2007), and three weeks later than last year. Chukchi Sea ice extent as of November 24 was similar to that on the same date 2007 and 2014.
Antarctic Sea Ice
Unlike the last two winters, Antarctic sea ice extent through mid-2016 was unremarkable though somewhat below average (Figure 4). Sea ice extent very closely tracked the 1982-2010 average and remained well below the previous two years’ extent, particularly 2014, until August-September. Recent years have shown a small positive trend in Antarctic sea ice extent during the Southern Hemispheric winter. Antarctic sea ice extent on September 1, 2016 was 7.04 million square miles (18.245 million square kilometers), which was 375,000 square miles (971,250 square kilometers) less than the ice extent on that date in 2014 (7.42 million square miles or 19.206 million square kilometers).
Since late August, however, Antarctic sea ice extent has been substantially below average. In fact, only the 1986 spring extent was lower.
Fig. 4. Antarctic sea ice extent for 2016, with means from the 1980s, 1990s, and 2000s, and with ice extents for 2012, 2013, and 2014. Credit: JAXA/NiPR.
Wang, X., J. Key, R. Kwok, and J. Zhang, 2016, Comparison of sea ice thickness from satellites, aircraft, and PIOMAS data, Remote. Sens., 8, 713, doi:10.3390/rs8090713.