Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica
Katabatic winds in coastal polynyas expose the ocean to extreme heat loss, causing intense sea ice production and dense water formation around Antarctica throughout autumn and winter. The advancing sea ice pack, combined with high winds and low temperatures, has limited surface ocean observations of...
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ftcopernicus:oai:publications.copernicus.org:tc79984 2023-05-15T13:31:39+02:00 Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica Thompson, Lisa Smith, Madison Thomson, Jim Stammerjohn, Sharon Ackley, Steve Loose, Brice 2020-10-06 application/pdf https://doi.org/10.5194/tc-14-3329-2020 https://tc.copernicus.org/articles/14/3329/2020/ eng eng doi:10.5194/tc-14-3329-2020 https://tc.copernicus.org/articles/14/3329/2020/ eISSN: 1994-0424 Text 2020 ftcopernicus https://doi.org/10.5194/tc-14-3329-2020 2020-10-12T16:22:14Z Katabatic winds in coastal polynyas expose the ocean to extreme heat loss, causing intense sea ice production and dense water formation around Antarctica throughout autumn and winter. The advancing sea ice pack, combined with high winds and low temperatures, has limited surface ocean observations of polynyas in winter, thereby impeding new insights into the evolution of these ice factories through the dark austral months. Here, we describe oceanic observations during multiple katabatic wind events during May 2017 in the Terra Nova Bay and Ross Sea polynyas. Wind speeds regularly exceeded 20 m s −1 , air temperatures were below −25 ∘ C, and the oceanic mixed layer extended to 600 m. During these events, conductivity–temperature–depth (CTD) profiles revealed bulges of warm, salty water directly beneath the ocean surface and extending downwards tens of meters. These profiles reflect latent heat and salt release during unconsolidated frazil ice production, driven by atmospheric heat loss, a process that has rarely if ever been observed outside the laboratory. A simple salt budget suggests these anomalies reflect in situ frazil ice concentration that ranges from 13 to <math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">266</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">3</mn></mrow></msup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="f625808186b432fb2b94460aefb19756"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="tc-14-3329-2020-ie00001.svg" width="54pt" height="14pt" src="tc-14-3329-2020-ie00001.png"/></svg:svg> kg m −3 . Contemporaneous estimates of vertical mixing reveal rapid convection in these unstable density profiles and mixing lifetimes from 7 to 12 min. The individual estimates of ice production from the salt budget reveal the intensity of short-term ice production, up to 110 cm d −1 during the windiest events, and a seasonal average of 29 cm d −1 . We further found that frazil ice production rates covary with wind speed and with location along the upstream–downstream length of the polynya. These measurements reveal that it is possible to indirectly observe and estimate the process of unconsolidated ice production in polynyas by measuring upper-ocean water column profiles. These vigorous ice production rates suggest frazil ice may be an important component in total polynya ice production. Text Antarc* Antarctica ice pack Ross Sea Sea ice Copernicus Publications: E-Journals Austral Ross Sea Terra Nova Bay The Cryosphere 14 10 3329 3347 |
institution |
Open Polar |
collection |
Copernicus Publications: E-Journals |
op_collection_id |
ftcopernicus |
language |
English |
description |
Katabatic winds in coastal polynyas expose the ocean to extreme heat loss, causing intense sea ice production and dense water formation around Antarctica throughout autumn and winter. The advancing sea ice pack, combined with high winds and low temperatures, has limited surface ocean observations of polynyas in winter, thereby impeding new insights into the evolution of these ice factories through the dark austral months. Here, we describe oceanic observations during multiple katabatic wind events during May 2017 in the Terra Nova Bay and Ross Sea polynyas. Wind speeds regularly exceeded 20 m s −1 , air temperatures were below −25 ∘ C, and the oceanic mixed layer extended to 600 m. During these events, conductivity–temperature–depth (CTD) profiles revealed bulges of warm, salty water directly beneath the ocean surface and extending downwards tens of meters. These profiles reflect latent heat and salt release during unconsolidated frazil ice production, driven by atmospheric heat loss, a process that has rarely if ever been observed outside the laboratory. A simple salt budget suggests these anomalies reflect in situ frazil ice concentration that ranges from 13 to <math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">266</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">3</mn></mrow></msup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="f625808186b432fb2b94460aefb19756"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="tc-14-3329-2020-ie00001.svg" width="54pt" height="14pt" src="tc-14-3329-2020-ie00001.png"/></svg:svg> kg m −3 . Contemporaneous estimates of vertical mixing reveal rapid convection in these unstable density profiles and mixing lifetimes from 7 to 12 min. The individual estimates of ice production from the salt budget reveal the intensity of short-term ice production, up to 110 cm d −1 during the windiest events, and a seasonal average of 29 cm d −1 . We further found that frazil ice production rates covary with wind speed and with location along the upstream–downstream length of the polynya. These measurements reveal that it is possible to indirectly observe and estimate the process of unconsolidated ice production in polynyas by measuring upper-ocean water column profiles. These vigorous ice production rates suggest frazil ice may be an important component in total polynya ice production. |
format |
Text |
author |
Thompson, Lisa Smith, Madison Thomson, Jim Stammerjohn, Sharon Ackley, Steve Loose, Brice |
spellingShingle |
Thompson, Lisa Smith, Madison Thomson, Jim Stammerjohn, Sharon Ackley, Steve Loose, Brice Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica |
author_facet |
Thompson, Lisa Smith, Madison Thomson, Jim Stammerjohn, Sharon Ackley, Steve Loose, Brice |
author_sort |
Thompson, Lisa |
title |
Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica |
title_short |
Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica |
title_full |
Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica |
title_fullStr |
Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica |
title_full_unstemmed |
Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica |
title_sort |
frazil ice growth and production during katabatic wind events in the ross sea, antarctica |
publishDate |
2020 |
url |
https://doi.org/10.5194/tc-14-3329-2020 https://tc.copernicus.org/articles/14/3329/2020/ |
geographic |
Austral Ross Sea Terra Nova Bay |
geographic_facet |
Austral Ross Sea Terra Nova Bay |
genre |
Antarc* Antarctica ice pack Ross Sea Sea ice |
genre_facet |
Antarc* Antarctica ice pack Ross Sea Sea ice |
op_source |
eISSN: 1994-0424 |
op_relation |
doi:10.5194/tc-14-3329-2020 https://tc.copernicus.org/articles/14/3329/2020/ |
op_doi |
https://doi.org/10.5194/tc-14-3329-2020 |
container_title |
The Cryosphere |
container_volume |
14 |
container_issue |
10 |
container_start_page |
3329 |
op_container_end_page |
3347 |
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1766019744848150528 |