Sea Ice and Freshwater Ice Assessments
2019 Sea Ice
Jeff Key and Rick Thoman
6 January 2019; updated 18 January, 7 March, 10 July
Note: This is an early and partial assessment for 2019. It will be updated and expanded periodically througout the year.
Record Minimum Antarctic Sea Ice Extent for Early January and June
On 1 January 2019, the sea ice area around the Antarctic continent was the smallest January area since the satellite record began in 1978. Figure 1 shows time series of ice extent from two sources. The sea ice area was 30,044 sq km (11,600 sq mi) below the previous record low for 1 January, which was set in 2017. Figure 2 shows the sea ice extent from AMSR2 on 1 January 2018 and 1 January 2019. The largest differences are in the Davis Sea (~75°E longitude) and the Ross Sea (~175°W). The melt season will continue into February. By February the minimum Antarctic sea ice extent was no longer a record. However, in June it was the lowest mean monthly extent for that month (Figure 1, middle and right), surpassing 2002 and 2017.
Fig. 1. Antarctic sea ice extent through early January (left) and through July 2019 (middle and right). Left and right: NSIDC; middle: JAXA/NiPR/ADS.
Fig. 2. Antarctic sea ice extent on 1 January 2018 (left) and 1 January 2019 (right). (NOAA)
Antarctic sea ice cover is highly variable. For example, it reached a record high in 2014 and a record low in 2016 (Figure 3). Why is the Antarctic sea ice extent so low? There is some discussion that suggests it's a combination of natural variability in the atmosphere and ocean, with a possible role of human-induced changes in the climate system. For the 2016 record minimum, it appears that a strongly negative Indian Ocean Dipole (IOD) event promoted a wind pattern such that surface winds from the north pushed the sea ice back towards the Antarctic continent and also brought additional heat to the region, enhancing ice melt. That 2016 pattern may have a longer-term impact that has led to the current low sea ice extent event.
Fig. 3. Annual cycle of Antarctic sea ice extent in 2014 and 2016 with the 1981-2010 median. (NSIDC's Charctic tool)
Anomalous Winter Transition to Open Water for Western Alaska…Again
Looking back, the winter of 2017-18 produced unprecedented low sea ice coverage in the Bering Sea. A number of western Alaskan communities battled the all-too-familiar coastal flooding during the autumn and into the winter, culminating with unprecedented flooding at Little Diomede during late February. Maritime subsistence harvest activities were modified with increased financial costs and public safety risks - or altogether abandoned. Beginning in late spring, seabirds and subadult seals were emaciated or in poor body condition. The late winter 2018 ice extent was significantly lower than any reconstructed ice extent records since 1850. Summer came and revealed profound changes in the northern Bering Sea marine ecosystem due to the lack of the thermal barrier formed by the briny waters that are created by sea ice formation. This dense salty water, which can remain liquid to -2°C, historically separated two distinct marine ecosystems (northern and southern Bering Sea). With limited sea ice formation in the northern Bering Sea, this barrier was almost entirely removed, allowing the larger predatory commercially, viable southern fishes to surge north.
Autumn 2018 started with very warm ocean temperatures in the southern Chukchi and Bering Seas and, as a result, sea ice was again slow to form. However, seasonably cold temperatures and frequent north winds during December 2018 and early January 2019 allowed for rapid ice growth and optimism for more normal spring sea ice conditions. But it was not to be: starting in late January the weather changed to persistent southerly storm conditions, with 15 separate storm systems affecting the northern Bering Sea region through February. This “parade of storms” decimated the existing sea ice by melting or pushing the ice north through the Bering Strait and into the in the southern Chukchi Sea (Figure 4). The impacts to coastal communities are immediate, and people are left to change their food-gathering strategies to a novel open water winter situation in order to provide for the nutritional, cultural, and economic needs of their families.
Overall, the February 2018 sea ice extent in the Bering Sea was the lowest record in the satellite era (since 1979), just 42% of the 1981-2010 average. Sea ice extent during February 2019 is the second lowest documented, at 56% of average. Sea ice extent in Alaska during March 2019 is not off to a good start, as there is already much less sea ice than at the same time in 2018.
Fig. 4. Sea ice concentration on 1 March 2019 (left) and 1 March 2018 (right). (Courtesy of University of Bremen and @AlaskaWx)