Water Science and Technology; Earth-Surface Processes
Abstract :
[en] Arctic sea ice has undergone significant changes over the past 50 years. Modern large-scale estimates of sea ice thickness and volume come from satellite observations. However, these estimates have limited accuracy, especially during the melt season, making it difficult to compare the Arctic sea ice state year to year. Uncertainties in sea ice density lead to high uncertainties in ice thickness retrieval from its freeboard. During the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition, we observed a first-year ice (FYI) freeboard increase of 0.02 m, while its thickness decreased by 0.5 m during the Arctic melt season in June-July 2020. Over the same period, the FYI density decreased from 910 to 880 kg m-3, and the sea ice air fraction increased from 1 % to 6 %, due to air void expansion controlled by internal melt. This increase in air volume substantially affected FYI density and freeboard. Due to differences in sea ice thermodynamic state (such as salinity and temperature), the air volume expansion is less pronounced in second-year ice (SYI) and has a smaller impact on the density evolution of SYI and ridges. We validated our discrete measurements of FYI density from coring using co-located ice topography observations from underwater sonar and an airborne laser scanner. Despite decreasing ice thickness, a similar counterintuitive increasing ice freeboard was observed for the entire 0.9 km2 MOSAiC ice floe, with a stronger freeboard increase for FYI than for less saline SYI. The surrounding 50 km2 area experienced a slightly lower 0.01 m ice freeboard increase in July 2020, despite comparable 0.5 m melt rates obtained from ice mass balance buoys. The increasing sea ice air volume defines the rapid decrease in FYI density, complicates the retrieval of ice thickness from satellite altimeters during the melt season, and underlines the importance of considering air volume and density changes in retrieval algorithms.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Salganik, Evgenii ; Norwegian Polar Institute, Fram Centre, Tromsø, Norway
Crabeck, Odile ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO) ; Laboratoire de Glaciologie, Université Libre de Bruxelles, Brussels, Belgium
Fuchs, Niels ; Institute of Oceanography, University of Hamburg, Hamburg, Germany
Hutter, Nils; Geomar Helmholtz Centre for Ocean Research Kiel, Kiel, Germany ; Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
Anhaus, Philipp ; Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany ; Institut für Den Schutz Maritimer Infrastrukturen, Deutsches Zentrum für Luft- und Raumfahrt E. V., Bremerhaven, Germany
Landy, Jack Christopher ; Department of Physics and Technology, UiT Arctic University of Norway, Tromsø, Norway
Language :
English
Title :
Impacts of air fraction increase on Arctic sea ice density, freeboard, and thickness estimation during the melt season
Norges Forskningsråd BMBF - Bundesministerium für Bildung und Forschung UW - University of Washington DFG - Deutsche Forschungsgemeinschaft F.R.S.-FNRS - Fonds de la Recherche Scientifique ERC - European Research Council
Funding text :
The work carried out and the data used in this paper are part of the international Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) with the tag MOSAiC20192020. We thank all persons involved in the expedition of the Research Vessel Polarstern (Alfred-Wegener- Institut Helmholtz-Zentrum f\u00FCr Polar- und Meeresforschung, 2017) during MOSAiC in 2019-2020 (Project_ID: AWI_PS122_00) as listed in Nixdorf et al. (2021). We especially acknowledge Mats A. Granskog, Marcel Nicolaus, and Donald Perovich for their efforts in coordinating the sea ice physics work during MOSAiC. We are also grateful to Marcel Nicolaus for his efforts in coordinating the ROV work during MOSAiC and to Christian Katlein for processing ROV multibeam sonar data. Evgenii Salganik and Jack Landy were supported by Research Council of Norway project INTERAAC (grant no. 328957). Odile Crabeck was supported by the FRS-FNRS (Research Credit MOSAiC J.0051.20 and Research Project Sea Ice Spray - T.0061.23). Odile Crabeck was also supported by the FRSFNRS Fellowship (grant 1.B.103.21F) and GreenFeedBack (Greenhouse gas fluxes and earth system feedbacks) funded by the European Union's HORIZON research and innovation program under grant agreement no. 101056921. ROV operations were jointly supported by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF) through the Diatom ARCTIC project (BMBF grant no. 03F0810A). Data processing and the position of Nils Hutter were partly funded by German Federal Ministry of Education and Research (BMBF) project IceSense - Remote Sensing of the Seasonal Evolution of Climate-relevant Sea Ice Properties (03F0866A). Niels Fuchs acknowledges funding from the BMBF project Nice- LABpro (03F0867A) and from the Deutsche Forschungsgemeinschaft under Germany's Excellence Strategy (EXC 2037; CLICCS - Climate, Climatic Change, and Society; project no. 390683824). Philipp Anhaus was supported by the BMBF through the Diatom ARCTIC project (BMBF grant no. 03F0810A) and the IceScan project (BMBF grant no. 03F0916A). Jack Landy was additionally supported by the European Research Council project SI/3D (grant no. 101077496). The authors thank Harry Heorton and three anonymous reviewers for their constructive suggestions, which helped to improve the paper. This research has been supported by the Norges Forskningsr\u00E4d (grant no. 328957), the Bundesministerium f\u00FCr Bildung und Forschung (grant nos. 03F0810A, 03F0866A, 03F0867A, and 03F0916A), the Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington (grant no. NA20OAR4320271), the Deutsche Forschungsgemeinschaft (grant no. 390683824), the Fonds De La Recherche Scientifique - FNRS (grant nos. 1.B.103.21F, J.0051.20, and T.0061.23), and the HORIZON EUROPE European Research Council (grant no. 101056921).This research has been supported by the Norges Forskningsr\u00E5d (grant no. 328957), the Bundesministerium f\u00FCr Bildung und Forschung (grant nos. 03F0810A, 03F0866A, 03F0867A, and 03F0916A), the Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington (grant no. NA20OAR4320271), the Deutsche Forschungsgemeinschaft (grant no. 390683824), the Fonds De La Recherche Scientifique \u2013 FNRS (grant nos. 1.B.103.21F, J.0051.20, and T.0061.23), and the HORIZON EUROPE European Research Council (grant no. 101056921).Evgenii Salganik and Jack Landy were supported by Research Council of Norway project INTERAAC (grant no. 328957). Odile Crabeck was supported by the FRS-FNRS (Research Credit MOSAiC J.0051.20 and Research Project Sea Ice Spray \u2013 T.0061.23). Odile Crabeck was also supported by the FRS-FNRS Fellowship (grant 1.B.103.21F) and GreenFeedBack (Greenhouse gas fluxes and earth system feedbacks) funded by the European Union's HORIZON research and innovation program under grant agreement no. 101056921. ROV operations were jointly supported by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF) through the Diatom ARCTIC project (BMBF grant no. 03F0810A). Data processing and the position of Nils Hutter were partly funded by German Federal Ministry of Education and Research (BMBF) project IceSense \u2013 Remote Sensing of the Seasonal Evolution of Climate-relevant Sea Ice Properties (03F0866A). Niels Fuchs acknowledges funding from the BMBF project NiceLABpro (03F0867A) and from the Deutsche Forschungsgemeinschaft under Germany's Excellence Strategy (EXC 2037; CLICCS \u2013 Climate, Climatic Change, and Society; project no. 390683824). Philipp Anhaus was supported by the BMBF through the Diatom ARCTIC project (BMBF grant no. 03F0810A) and the IceScan project (BMBF grant no. 03F0916A). Jack Landy was additionally supported by the European Research Council project SI/3D (grant no. 101077496).
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