Winter 2019/2020: Low sea-ice volume in the Arctic

3 April 2020

Combining satellite observations of sea-ice area and thickness allows us to compute the total amount of sea ice in the Arctic. The standard unit used for the sea-ice volume is thousands of cubic kilometres, and offers a better measure of the state of Arctic sea ice than the extent, since the volume includes the thickness of the ice layer and not merely its total area. In recent years, changes in sea-ice volume have typically ranged from 5,000 cubic kilometres for the minimum extent in October, to 20,000 for the maximum extent in April.

To compute sea-ice volume, seamless ice thickness information is required. This can be achieved by merging data from the two ESA satellites CryoSat-2 and SMOS, but the method is limited to the Arctic winter months, from October to April. Creating such a dataset is the purpose of the “SMOS & CryoSat-2 Sea Ice Data Product Processing and Dissemination Service (CS2SMOS-PDS)” project, which started  in October 2019 to provide consistent sea-ice thickness information on the Northern Hemisphere, with daily updates (Video 1). Both the CryoSat-2 and SMOS satellite have been providing sea-ice thickness data since November 2010 and will soon deliver a 10-year long data record for scientific analysis.

The sea-ice volume computed from the CryoSat-2/SMOS observations for January 2020 shows the second-lowest volume since the beginning of the time series (Figure 1). The value for 31 January 2020 was 15,040 cubic kilometres, which is 1,084 cubic kilometres less than the average value for this date. Due to the well-documented decline in sea-ice extent and thickness due to the loss of older ice, it’s highly probable that January 2020 had the second-lowest volume in the last several decades, and not just in the CryoSat-2/SMOS time series.

The low ice volume is a product of moderate sea-ice extent and wider stretches of below-average thicknesses in the central Arctic Ocean (Figure 2). Above-average thicknesses were only to be found in the Beaufort, Barents and Kara Seas. These regionally limited patterns were fairly consistent throughout the winter months, and were already apparent in October 2019. This indicates that the patterns began in the melting season of the previous summer, and subsequently prevailed through the first four months of the winter season. 

The Arctic sea-ice will most likely gain an additional 5,000 cubic kilometres of volume before the start of the melting season. We won’t be able to make a final assessment of the current season until June, when all the CryoSat-2 and SMOS data is available.

Dr Stefan Hendricks