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The Daily-Resolved Southern Ocean Mixed Layer: Regional Contrasts Assessed Using Glider Observations

du Plessis, M. D. and Swart, S. and Biddle, L. C. and Giddy, I. S. and Monteiro, P. M. S. and Reason, C. J. C. and Thompson, A. F. and Nicholson, S.-A. (2022) The Daily-Resolved Southern Ocean Mixed Layer: Regional Contrasts Assessed Using Glider Observations. Journal of Geophysical Research. Oceans, 127 (4). Art. No. e2021JC017760. ISSN 2169-9275. doi:10.1029/2021jc017760. https://resolver.caltech.edu/CaltechAUTHORS:20220325-172915787

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Abstract

Water mass transformation in the Southern Ocean is vital for driving the large-scale overturning circulation, which transports heat from the surface to the ocean interior. Using profiling gliders, this study investigates the role of summertime buoyancy forcing and wind-driven processes on the intraseasonal (1–10 days) mixed layer thermohaline variability in three Southern Ocean regions southwest of Africa important for water mass transformation—the Subantarctic Zone (SAZ), Polar Frontal Zone (PFZ), and Marginal Ice Zone (MIZ). At intraseasonal time scales, heat flux was shown as the main driver of buoyancy gain in all regions. In the SAZ and MIZ, shallow mixed layers and strong stratification enhanced mixed layer buoyancy gain by trapping incoming heat, while buoyancy loss resulted primarily from the entrainment of cold, salty water from below. In the PFZ, rapid mixing linked to Southern Ocean storms set persistently deep mixed layers and suppressed mixed layer intraseasonal thermohaline variability. In the polar regions, lateral stirring of meltwater from seasonal sea-ice melt dominated daily mixed layer salinity variability. We propose that these meltwater fronts are advected to the PFZ during late summer, indicating the potential for seasonal sea-ice freshwater to impact a region where the upwelling limb of overturning circulation reaches the surface. This study reveals a regional dependence of how the mixed layer thermohaline properties respond to small spatiotemporal processes, emphasizing the importance of surface forcing occurring between 1 and 10 days on the mixed layer water mass transformation in the Southern Ocean.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1029/2021JC017760DOIArticle
http://www.ecmwf.int/en/forecasts/datasets/archive-datasets/reanalysis-datasets/era5Related ItemData
http://data.meereisportal.de/data/iup/hdf/s/Related ItemData
https://www.metoffice.gov.uk/hadobs/en4/download-en4-2-1.htmlRelated ItemData
http://www.aviso.altimetry.fr/en/data/data-access/gridded-data-extraction-tool.htmlRelated ItemData
http://doi.org/10.5281/zenodo.5076119DOIData
http://doi.org/10.5281/zenodo.5079763DOIData
ORCID:
AuthorORCID
du Plessis, M. D.0000-0003-2759-2467
Swart, S.0000-0002-2251-8826
Biddle, L. C.0000-0002-4785-1959
Giddy, I. S.0000-0002-8926-3311
Monteiro, P. M. S.0000-0003-0425-0552
Reason, C. J. C.0000-0002-3224-5243
Thompson, A. F.0000-0003-0322-4811
Nicholson, S.-A.0000-0002-1226-1828
Additional Information:© 2022 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. Issue Online: 05 April 2022; Version of Record online: 05 April 2022; Accepted manuscript online: 23 March 2022; Manuscript accepted: 07 March 2022; Manuscript revised: 01 March 2022; Manuscript received: 16 July 2021. This work was supported by the following grants of S. Swart: Wallenberg Academy Fellowship (WAF 2015.0186), Swedish Research Council (VR 2019-04400), STINT-NRF Mobility Grant and NRF-SANAP (SNA170522231782 and SANAP200324510487 with S. Nicholson as PI). S. Swart and M. du Plessis have received funding from the European Union's Horizon 2020 research and innovation program under Grant Agreement 821001 (SO-CHIC) an M. du Plessis was later funded by the European Union's Marie Skłodowska Curie Individual Fellowship under the Horizon 2020 framework with Project ID 101032683. L. Biddle is additionally supported by a Swedish Research Council grant (VR 2020 04281) The authors thank Sea Technology Services (STS), SANAP, the captain, and crew of the S.A. Agulhas II for their field-work/technical assistance. Zach Erickson, Mar Flexas, and Giuliana Viglione (Caltech) contributed to glider piloting throughout the MIZ deployment. The authors thank David Peddie of Offshore Sensing AS for assistance with the Sailbuoy deployment. The authors are grateful to Geoff Shilling and Craig Lee (APL, University of Washington) for hosting the gliders on IOP and the technical advice provided. The authors thank three anonymous reviewers, whose constructive reviews greatly improved this manuscript. Data Availability Statement: ERA5 data are generated using Copernicus Climate Change Service Information, available online at www.ecmwf.int/en/forecasts/datasets/archive-datasets/reanalysis-datasets/era5. The sea-ice data are made available via http://data.meereisportal.de/data/iup/hdf/s/. The EN4 data are made available via the UK Hadley Met Office at https://www.metoffice.gov.uk/hadobs/en4/download-en4-2-1.html. The ADT data used to determine the fronts are generated by the Archiving, Validation, and Interpretation of Satellite Oceanographic data service of Centre National D'Etudes Spatiales, available online www.aviso.altimetry.fr/en/data/data-access/gridded-data-extraction-tool.html. The code used for this analysis is available at http://doi.org/10.5281/zenodo.5076119 and the data at http://doi.org/10.5281/zenodo.5079763.
Funders:
Funding AgencyGrant Number
Knut and Alice Wallenberg FoundationWAF 2015.0186
Swedish Research CouncilVR 2019-04400
National Research Foundation (South Africa)SNA170522231782
National Research Foundation (South Africa)SANAP200324510487
European Research Council (ERC)821001
Marie Curie Fellowship101032683
Swedish Research CouncilVR 2020 04281
Subject Keywords:Gliders; Mixing; Heat Flux; Ocean Observations; Southern Ocean
Issue or Number:4
DOI:10.1029/2021jc017760
Record Number:CaltechAUTHORS:20220325-172915787
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20220325-172915787
Official Citation:du Plessis, M. D., Swart, S., Biddle, L. C., Giddy, I. S., Monteiro, P. M. S., Reason, C. J. C., et al. (2022). The daily-resolved Southern Ocean mixed layer: Regional contrasts assessed using glider observations. Journal of Geophysical Research: Oceans, 127, e2021JC017760. https://doi.org/10.1029/2021JC017760
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114079
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:25 Mar 2022 11:33
Last Modified:30 Jun 2022 18:39

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  • du Plessis, M. D. and Swart, S. and Biddle, L. C. and Giddy, I. S. and Monteiro, P. M. S. and Reason, C. J. C. and Thompson, A. F. and Nicholson, S.-A. The Daily-Resolved Southern Ocean Mixed Layer: Regional Contrasts Assessed Using Glider Observations. (deposited 25 Mar 2022 11:33) [Currently Displayed]

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