Supercooled Southern Ocean Waters

• Main Authors: Haumann, F. Alexander, Moorman, Ruth, Riser, Stephen C., Smedsrud, Lars H., Maksym, Ted, Wong, Annie P. S., Wilson, Earle A., Drucker, Robert, Talley, Lynne D., Johnson, Kenneth S., Key, Robert M., Sarmiento, Jorge L.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Geophysical Union 2020
• Subjects: Southern Ocean; supercooling; sea ice; ice shelf; observations; convection; Antarctic; Antarc*; Ice Shelf; Ice Shelves; Sea ice
• Online Access: https://doi.org/10.1029/2020gl090242

In cold polar waters, temperatures sometimes drop below the freezing point, a process referred to as supercooling. However, observational challenges in polar regions limit our understanding of the spatial and temporal extent of this phenomenon. We here provide observational evidence that supercooled waters are much more widespread in the seasonally iceâ€covered Southern Ocean than previously reported. In 5.8% of all analyzed hydrographic profiles south of 55°S, we find temperatures below the surface freezing point ("potential" supercooling), and half of these have temperatures below the local freezing point ("in situ" supercooling). Their occurrence doubles when neglecting measurement uncertainties. We attribute deep coastalâ€ocean supercooling to melting of Antarctic ice shelves and surfaceâ€induced supercooling in the seasonal seaâ€ice region to wintertime seaâ€ice formation. The latter supercooling type can extend down to the permanent pycnocline due to convective sinking plumes—an important mechanism for vertical tracer transport and waterâ€mass structure in the polar ocean. © 2020 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Issue Online: 22 October 2020; Version of Record online: 22 October 2020; Accepted manuscript online: 09 October 2020; Manuscript accepted: 26 September 2020; Manuscript revised: 23 September 2020; Manuscript received: 07 August 2020. F. A. H. was supported by the Swiss National Science Foundation (SNSF; Schweizerischer Nationalfonds zur Förderung der wissenschaftlichen Forschung) grant numbers P2EZP2_175162 and P400P2_186681. This work was supported by the National Science Foundation (NSF) Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) Project under the NSF Award PLRâ€1425989. R. M. would like to thank the National Oceanic and Atmospheric Administration (NOAA) GFDL for mentorship and ...