EGU21-3723, updated on 04 Mar 2021
https://doi.org/10.5194/egusphere-egu21-3723
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Winter upper-ocean thermohaline variability observed from drifting ice platforms in the Amundsen Basin, Arctic Ocean

Ying-Chih Fang1,2, Benjamin Rabe2, Ivan Kuznetsov2, Mario Hoppmann2, Sandra Tippenhauer2, Kirstin Schulz2, Julia Regnery2, Markus Janout2, Jan Rohde2, Jakob Belter2, Thomas Krumpen2, Marcel Nicolaus2, and the MOSAiC Ocean Team*
Ying-Chih Fang et al.
  • 1National Sun Yat-sen University, Department of Oceanography, Kaohsiung, Taiwan (ying-chih.fang@awi.de)
  • 2Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • *A full list of authors appears at the end of the abstract

We analyzed hydrographic data from several autonomous oceanographic buoys within the MOSAiC Distributed Network together with regular CTD casts from the MOSAiC Central Observatory during the 2019/20 winter in the Amundsen Basin. These drifting platforms can yield as small as ~300 m (or 10 min) horizontal resolution, providing unprecedented perspectives for the (sub)mesoscale dynamics. Full-depth CTD profiles yielded the first baroclinic Rossby radii (R1) of ~7.5 km, which is consistent with previous studies based on climatology. Near-surface layers shallower than the halocline were not always mixed. Restratification was commonly observed, suggesting the onset of baroclinic instabilities and/or eddies emanating from the lateral fronts. A surface-layer eddy with estimated radius of ~5 km was fortuitously observed and coincident with the surrounding mixed geostrophic shear in the vertical, that is, oppositely-sloping isopycnals within the depth range of ~20 – 200 m. This structure is reminiscent of the Charney-type baroclinic instability, resulting from a difference in the sign of the vertical gradient of the interior quasigeostrophic potential vorticity and that of the surface buoyancy forcing. A reconstructed surface dynamic height field supports this argument, showing that submesoscale to mesoscale surface lateral buoyancy gradients are ubiquitous. This result implies that the study domain could be inherently unstable and prone to generate baroclinic eddies. We also observed that the slopes of the density horizontal wavenumber spectra changed at the halocline depths (~40 – 75 m) after a ~3-day storm event with peak speeds ~ 20 m s-1. We hypothesize that such change could be related to the Ekman pumping due to large ice drift (~50 cm s-1) and its resultant stress curl during the storm. Our analyses underline that thinning Arctic sea ice and increasing ice drift could together trigger more oceanic heat flux into the cold halocline by storms, further deteriorating winter ice growth in the Amundsen Basin.

MOSAiC Ocean Team:

Jacob Allerholt , AWI ; Marylou Athanase , LOCEAN-IPSL ; Chris Basque , WHOI ; Dorothea Bauch , GEOMAR ; Till Baumann , UiB ; Dake Chen , SIO ; Silvia Cole , WHOI ; Sam Cornish , U Oxford ; Lisa Craw , U Tasmania ; Andrew Davies , WHOI ; Dmitry Divine , NPI/HAVOC ; Francesca Doglioni , AWI ; Falk Ebert , Herder-Gymnasium Berlin ; Carina Engicht , AWI ; Ying-Chih Fang , AWI ; Ilker Fer , UIB ; Mats Granskog , NPI/HAVOC ; Rainer Graupner , AWI ; Hailun He , SIO China ; Yan He , FIO ; Céline Heuzé , U Gotheburg ; Mario Hoppmann , AWI ; Markus Janout , AWI ; David Kadko , FIU ; Torsten Kanzow , AWI ; Salar Karam , U Gothenburg ; Yusuke Kawaguchi , Uni. Tokyo ; Zoe Koenig , UIB ; Bin Kong , FIO ; Rick Krishfield , WHOI ; David Kuhlmey , AWI ; Ivan Kuznetsov , AWI ; Musheng Lan , PRIC ; Ruibo Lei , PRIC ; Tao Li , OUC ; Long Lin , SIO ; Hailong Liu , SJTU ; Na Liu , FIO ; Xiaobing Ma , FIO ; Rosalie MacKay , NTNU ; Maria Mallet , AWI ; Robbie Mallet , UCL ; Wieslaw Maslowski , NPS ; Christian Mertens , Uni Bremen ; Volker Mohrholz , IOW ; Matthias Monsees , AWI ; Morven Muilwijk , UiB ; Jeff O'Brien , WHOI ; Algot Peterson , UIB ; Pierre Priou , U Newfoundland ; Benjamin Rabe , AWI ; Julia Regnery , AWI ; Jian Ren , SIO ; Natalia Ribeiro Santos , U Tasmania ; Janin Schaffer , AWI ; Ingo Schuffenhauer , IOW ; Kirstin Schulz , AWI ; William Shaw , NPS ; Timothy Stanton , NPS ; Mark Stephens , FIU ; Jie Su , OUC ; Natalia Sukhikh , Uni Bremen ; Arild Sundfjord , NPI/HAVOC ; Sandra Tippenhauer , AWI ; John Toole , WHOI ; Pedro Torre , NTNU ; Jutta Vernaleken , AWI ; Myriel Vredenborg , AWI ; Hangzhou Wang , ZJU ; Lei Wang , BMU ; Yuntao Wang , SIO ; Bai Youcheng , SIO ; Jinping Zhao , OUC ; Meng Zhou , SJTU ; Jialiang Zhu , OUC.

How to cite: Fang, Y.-C., Rabe, B., Kuznetsov, I., Hoppmann, M., Tippenhauer, S., Schulz, K., Regnery, J., Janout, M., Rohde, J., Belter, J., Krumpen, T., and Nicolaus, M. and the MOSAiC Ocean Team: Winter upper-ocean thermohaline variability observed from drifting ice platforms in the Amundsen Basin, Arctic Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3723, https://doi.org/10.5194/egusphere-egu21-3723, 2021.

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