Abstract
Abstract. Changes in Arctic sea ice thickness are the result of complex interactions of the dynamic and variable ice cover with atmosphere and ocean. Most of the sea ice exiting the Arctic Ocean does so through Fram Strait, which is why long-term measurements of ice thickness at the end of the Transpolar Drift provide insight into the integrated signals of thermodynamic and dynamic influences along the pathways of Arctic sea ice. We present an updated summer (July–August) time series of extensive ice thickness surveys carried out at the end of the Transpolar Drift between 2001 and 2020. Overall, we see a more than 20 % thinning of modal ice thickness since 2001. A comparison of this time series with first preliminary results from the international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) shows that the modal summer thickness of the MOSAiC floe and its wider vicinity are consistent with measurements from previous years at the end of the Transpolar Drift. By combining this unique time series with the Lagrangian sea ice tracking tool, ICETrack, and a simple thermodynamic sea ice growth model, we link the observed interannual ice thickness variability north of Fram Strait to increased drift speeds along the Transpolar Drift and the consequential variations in sea ice age. We also show that the increased influence of upward-directed ocean heat flux in the eastern marginal ice zones, termed Atlantification, is not only responsible for sea ice thinning in and around the Laptev Sea but also that the induced thickness anomalies persist beyond the Russian shelves and are potentially still measurable at the end of the Transpolar Drift after more than a year. With a tendency towards an even faster Transpolar Drift, winter sea ice growth will have less time to compensate for the impact processes, such as Atlantification, have on sea ice thickness in the eastern marginal ice zone, which will increasingly be felt in other parts of the sea-ice-covered Arctic.
Highlights
The Arctic sea ice cover is undergoing rapid changes
On the basis of airborne EM (AEM) surveys conducted over the DN regions (DNR) in April and early July 2020 and the already existing IceBird time series, we argue that the modal sea ice thickness (SIT) of 1.71 m measured on the MOSAiC floe is not just representative for the wider area around the floe and in line with measurements from previous years (Fig. 1b)
This study provides an important extension of the longterm electromagnetic induction (EM)-derived summer SIT time series at the end of the Transpolar Drift presented by Krumpen et al (2016)
Summary
The Arctic sea ice cover is undergoing rapid changes. Besides the continuous decline in annual mean sea ice extent by almost 14 % per decade from 1979 to 2010 (Cavalieri and Parkinson, 2012; Stroeve et al, 2012), sea ice volume has decreased as well. Based on a combination of submarine sea ice draft and satellite sea ice thickness (SIT) measurements from ICESat and CryoSat-2 from 1958 to 2018, Kwok (2018) found that central Arctic summer mean SIT decreased by Published by Copernicus Publications on behalf of the European Geosciences Union. Belter et al.: Interannual variability in Transpolar Drift summer sea ice thickness about 60 % over 6 decades. This thinning was accompanied by a reduction in second-year and multi-year ice (SYI and MYI) fraction of more than 50 %, which resulted in substantial sea ice volume loss (Kwok, 2018; Spreen et al, 2020)
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