Mixed layer depth seasonality modulates summertime SST variability in the Southern Ocean
In recent years, the Southern Ocean has experienced unprecedented surface warming and sea ice loss---a stark reversal of sea ice expansion and surface cooling trends that prevailed over preceding decades. The most dramatic changes occurred in the austral spring of 2016 when Antarctic sea-ice extent...
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ftcaltechauth:oai:authors.library.caltech.edu:115452 2023-05-15T13:52:02+02:00 Mixed layer depth seasonality modulates summertime SST variability in the Southern Ocean Wilson, Earle A. Bonan, David B. Thompson, Andrew F. Armstrong, Natalie Riser, Stephen C. 2022-07-10 application/pdf https://authors.library.caltech.edu/115452/ https://authors.library.caltech.edu/115452/1/essoar.10511825.1.pdf https://resolver.caltech.edu/CaltechAUTHORS:20220711-347656000 en eng https://authors.library.caltech.edu/115452/1/essoar.10511825.1.pdf Wilson, Earle A. and Bonan, David B. and Thompson, Andrew F. and Armstrong, Natalie and Riser, Stephen C. (2022) Mixed layer depth seasonality modulates summertime SST variability in the Southern Ocean. . (Unpublished) https://resolver.caltech.edu/CaltechAUTHORS:20220711-347656000 <https://resolver.caltech.edu/CaltechAUTHORS:20220711-347656000> cc_by_nc_nd CC-BY-NC-ND Report or Paper PeerReviewed 2022 ftcaltechauth 2022-07-14T17:54:28Z In recent years, the Southern Ocean has experienced unprecedented surface warming and sea ice loss---a stark reversal of sea ice expansion and surface cooling trends that prevailed over preceding decades. The most dramatic changes occurred in the austral spring of 2016 when Antarctic sea-ice extent (SIE) reached a record minimum as sea surface temperatures (SST) climbed to a near-record high. In late 2019, another circumpolar surface warming event spanned the Southern Ocean, albeit with no appreciable decline in Antarctic SIE. A mixed layer heat budget analysis reveals that these recent circumpolar surface warming events were triggered by a weakening of the circumpolar westerlies, which decreased northward Ekman transport and accelerated the seasonal shoaling of the mixed layer. The latter effect amplified the surface warming effect of air-sea heat fluxes during months of peak solar insolation. More generally, summertime SST across the Southern Ocean is sensitive to the timing of the springtime shoaling of the mixed layer, which is controlled by the strength and temporal variance of the circumpolar westerlies. An examination of the CESM1 large ensemble demonstrates that these recent circumpolar warming events are consistent with the internal variability associated with the Southern Annual Mode (SAM), whereby negative SAM in austral spring favors shallower mixed layers and anomalously high summertime SST. Thus, future Southern Ocean surface warming extremes will depend on the evolution of regional mixed layer depths and interannual SAM variability. Report Antarc* Antarctic Sea ice Southern Ocean Caltech Authors (California Institute of Technology) Antarctic Austral Southern Ocean |
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English |
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In recent years, the Southern Ocean has experienced unprecedented surface warming and sea ice loss---a stark reversal of sea ice expansion and surface cooling trends that prevailed over preceding decades. The most dramatic changes occurred in the austral spring of 2016 when Antarctic sea-ice extent (SIE) reached a record minimum as sea surface temperatures (SST) climbed to a near-record high. In late 2019, another circumpolar surface warming event spanned the Southern Ocean, albeit with no appreciable decline in Antarctic SIE. A mixed layer heat budget analysis reveals that these recent circumpolar surface warming events were triggered by a weakening of the circumpolar westerlies, which decreased northward Ekman transport and accelerated the seasonal shoaling of the mixed layer. The latter effect amplified the surface warming effect of air-sea heat fluxes during months of peak solar insolation. More generally, summertime SST across the Southern Ocean is sensitive to the timing of the springtime shoaling of the mixed layer, which is controlled by the strength and temporal variance of the circumpolar westerlies. An examination of the CESM1 large ensemble demonstrates that these recent circumpolar warming events are consistent with the internal variability associated with the Southern Annual Mode (SAM), whereby negative SAM in austral spring favors shallower mixed layers and anomalously high summertime SST. Thus, future Southern Ocean surface warming extremes will depend on the evolution of regional mixed layer depths and interannual SAM variability. |
format |
Report |
author |
Wilson, Earle A. Bonan, David B. Thompson, Andrew F. Armstrong, Natalie Riser, Stephen C. |
spellingShingle |
Wilson, Earle A. Bonan, David B. Thompson, Andrew F. Armstrong, Natalie Riser, Stephen C. Mixed layer depth seasonality modulates summertime SST variability in the Southern Ocean |
author_facet |
Wilson, Earle A. Bonan, David B. Thompson, Andrew F. Armstrong, Natalie Riser, Stephen C. |
author_sort |
Wilson, Earle A. |
title |
Mixed layer depth seasonality modulates summertime SST variability in the Southern Ocean |
title_short |
Mixed layer depth seasonality modulates summertime SST variability in the Southern Ocean |
title_full |
Mixed layer depth seasonality modulates summertime SST variability in the Southern Ocean |
title_fullStr |
Mixed layer depth seasonality modulates summertime SST variability in the Southern Ocean |
title_full_unstemmed |
Mixed layer depth seasonality modulates summertime SST variability in the Southern Ocean |
title_sort |
mixed layer depth seasonality modulates summertime sst variability in the southern ocean |
publishDate |
2022 |
url |
https://authors.library.caltech.edu/115452/ https://authors.library.caltech.edu/115452/1/essoar.10511825.1.pdf https://resolver.caltech.edu/CaltechAUTHORS:20220711-347656000 |
geographic |
Antarctic Austral Southern Ocean |
geographic_facet |
Antarctic Austral Southern Ocean |
genre |
Antarc* Antarctic Sea ice Southern Ocean |
genre_facet |
Antarc* Antarctic Sea ice Southern Ocean |
op_relation |
https://authors.library.caltech.edu/115452/1/essoar.10511825.1.pdf Wilson, Earle A. and Bonan, David B. and Thompson, Andrew F. and Armstrong, Natalie and Riser, Stephen C. (2022) Mixed layer depth seasonality modulates summertime SST variability in the Southern Ocean. . (Unpublished) https://resolver.caltech.edu/CaltechAUTHORS:20220711-347656000 <https://resolver.caltech.edu/CaltechAUTHORS:20220711-347656000> |
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CC-BY-NC-ND |
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1766256227242737664 |