Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica

• Published in: The Cryosphere
• Main Authors: L. Thompson, M. Smith, J. Thomson, S. Stammerjohn, S. Ackley, B. Loose
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2020
• Subjects: Environmental sciences; GE1-350; Geology; QE1-996.5; Austral; Ross Sea; Terra Nova Bay; Antarc*; Antarctica; ice pack; Sea ice; The Cryosphere
• Online Access: https://doi.org/10.5194/tc-14-3329-2020; https://doaj.org/article/2c26400b04d9418892f50cb623cac52c

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 ...