Preprints
https://doi.org/10.5194/tc-2020-375
https://doi.org/10.5194/tc-2020-375

  16 Feb 2021

16 Feb 2021

Review status: this preprint is currently under review for the journal TC.

Arctic sea ice anomalies during the MOSAiC winter 2019/20

Klaus Dethloff1, Wieslaw Maslowski2, Stefan Hendricks3, Younjoo Lee2, Helge F. Goessling3, Thomas Krumpen3, Christian Haas3, Dörthe Handorf1, Robert Ricker3, Vladimir Bessonov4, John J. Cassano5, Jaclyn Clement Kinney2, Robert Osinski6, Markus Rex1, Annette Rinke1, Julia Sokolova4, and Anja Sommerfeld1 Klaus Dethloff et al.
  • 1Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Telegrafenberg A45, 14473 Potsdam, Germany
  • 2Department of Oceanography, Graduate School of Engineering and Applied Sciences, Naval Postgraduate School, Monterey, CA 93943, US
  • 3Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
  • 4Arctic and Antarctic Research Institute, Center Ice and Hydrometeorological Information, Bering Street 38, St. Petersburg, Russia
  • 5Cooperative Institute for Research in Environmental Sciences, National Snow and Ice Data Center and Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, US
  • 6Institute of Oceanology, Polish Academy of Sciences, Sopot 81712, Poland

Abstract. As the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) project went into effect during the winter of 2019/2020, the Arctic Oscillation (AO) has experienced some of the largest shifts from a highly negative index in November 2019 to an extremely positive index during January-February-March (JFM) 2020. Here we analyse the sea ice thickness (SIT) distribution based on CryoSat-2/SMOS satellite data augmented with results from the hindcast simulation by the fully coupled Regional Arctic System Model (RASM) for the time period from November 2019 through March 2020. A notable result of the positive AO phase during JFM 2020 were large SIT anomalies, up to 1.3 m, which emerged in the Barents-Sea (BS), along the northeastern Canadian coast and in parts of the central Arctic Ocean. These anomalies appear to be driven by nonlinear interactions between thermodynamic and dynamic processes. In particular, in the Barents- and Kara Seas (BKS) they are a result of an enhanced ice growth connected with the colder temperature anomalies and the consequence of intensified atmospheric-driven sea ice transport and deformations (i.e. divergence and shear) in this area. Low-pressure anomalies, which developed over the Eastern Arctic during JFM 2020, increased northerly winds from the cold Arctic Ocean to the BS and accelerated the southward drift of the MOSAiC ice floe. The satellite-derived and model-simulated sea ice velocity anomalies, which compared well during JFM 2020, indicate a strong acceleration of the Transpolar Drift relative to the mean for the past decade, with intensified speeds up to 6 km/day. As a consequence, sea ice transport and deformations driven by atmospheric wind forcing accounted for bulk of SIT anomalies, especially in January and February 2020. The unusual AO shift and the related sea ice anomalies during the MOSAiC winter 2019/20 are within the range of simulated states in the forecast ensemble. RASM intra-annual ensemble forecast simulations, forced with different atmospheric boundary conditions from November 1, 2019 through April 30, 2020, show a pronounced internally generated variability in the sea ice volume. A comparison of the respective SIT distribution and turbulent heat fluxes during the positive AO phase in JFM 2020 and the negative AO phase in JFM 2010 further corroborates the conclusion, that winter sea ice conditions of the Arctic Ocean can be significantly altered by AO variability.

Klaus Dethloff et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2020-375', Anonymous Referee #1, 02 Mar 2021
  • RC2: 'Comment on tc-2020-375', Anonymous Referee #2, 31 Mar 2021

Klaus Dethloff et al.

Klaus Dethloff et al.

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Short summary
Sea ice thickness anomalies during the MOSAiC project (Multidisciplinary drifting Observatory for the Study of Arctic Climate) in January, February and March 2020 have been simulated with the fully coupled regional Arctic climate system model (RASM) and compared with satellite data of CryoSat-2/SMOS. Hindcast and ensemble simulations indicate that these ice anomalies are driven by nonlinear interactions between thermodynamic ice growth and deformation processes and dynamic sea-ice transports.