Freshwater Input and Vertical Mixing in the Canada Basin’s Seasonal Halocline: 1975 versus 2006–12

Journal Article · 30 June 2022 · Journal of Physical Oceanography

DOI: https://doi.org/10.1175/JPO-D-21-0116.1 · OSTI ID:1872475

Rosenblum, Erica ^[1]; Stroeve, Julienne ^[2]; Gille, Sarah T. ^[3]; Lique, Camille ^[4]; Fajber, Robert ^[5]; Tremblay, L. Bruno ^[6]; Galley, Ryan ^[7]; Loureiro, Thiago ^[8]; Barber, David G. ^[1]; Lukovich, Jennifer V. ^[1]

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1. a Centre for Earth Observation Science, University of Manitoba, Winnipeg, Manitoba, Canada
2. a Centre for Earth Observation Science, University of Manitoba, Winnipeg, Manitoba, Canada, b Centre for Polar Observation and Modelling, Earth Sciences, University College London, London, United Kingdom, c National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado
3. d Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California
4. e Univ. Brest, CNRS, IRD, Ifremer, Laboratoire d’Océanographie Physique et Spatiale, IUEM, Brest, France
5. f Department of Physics, University of Toronto, Toronto, Ontario, Canada
6. g Department of Atmospheric Science, McGill University, Montreal, Quebec, Canada
7. h Department of Environment and Geography, University of Manitoba, Winnipeg, Manitoba, Canada
8. i Ryerson University, Toronto, Ontario, Canada

Abstract The Arctic seasonal halocline impacts the exchange of heat, energy, and nutrients between the surface and the deeper ocean, and it is changing in response to Arctic sea ice melt over the past several decades. Here, we assess seasonal halocline formation in 1975 and 2006–12 by comparing daily, May–September, salinity profiles collected in the Canada Basin under sea ice. We evaluate differences between the two time periods using a one-dimensional (1D) bulk model to quantify differences in freshwater input and vertical mixing. The 1D metrics indicate that two separate factors contribute similarly to stronger stratification in 2006–12 relative to 1975: 1) larger surface freshwater input and 2) less vertical mixing of that freshwater. The larger freshwater input is mainly important in August–September, consistent with a longer melt season in recent years. The reduced vertical mixing is mainly important from June until mid-August, when similar levels of freshwater input in 1975 and 2006–12 are mixed over a different depth range, resulting in different stratification. These results imply that decadal changes to ice–ocean dynamics, in addition to freshwater input, significantly contribute to the stronger seasonal stratification in 2006–12 relative to 1975. These findings highlight the need for near-surface process studies to elucidate the impact of lateral processes and ice–ocean momentum exchange on vertical mixing. Moreover, the results may provide insight for improving the representation of decadal changes to Arctic upper-ocean stratification in climate models that do not capture decadal changes to vertical mixing.

• Research Organization: Univ. of California, San Diego, CA (United States)
• Sponsoring Organization: National Oceanic and Atmospheric Administration (NOAA); National Science Foundation (NSF); USDOE; USDOE Office of Science (SC)
• Grant/Contract Number: SC0020073
• OSTI ID: 1872475
• Journal Information: Journal of Physical Oceanography, Journal Name: Journal of Physical Oceanography Journal Issue: 7 Vol. 52; ISSN 0022-3670
• Publisher: American Meteorological SocietyCopyright Statement
• Country of Publication: United States
• Language: English