A possible link between the Weddell Polynya and the Southern Annular Mode

Publication Type  Journal Article
Year of Publication  2007
Authors  Gordon, A. L.; Visbeck, M.; Comiso, J. C.
Journal Title  Journal of Climate
Volume  20
Issue  11
Pages  2558-2571
Journal Date  Jun 1
ISBN Number  0894-8755
Accession Number  ISI:000247159300014
Key Words  antarctic circumpolar current; winter mixed layer; sea-ice extent; maud rise; deep-water; extratropical circulation; synchronous variability; overturning circulation; hemisphere atmosphere; ocean
Abstract  

Shortly after the advent of the first imaging passive microwave sensor on board a research satellite an anomalous climate feature was observed within the Weddell Sea. During the years 1974-1976, a 250 x 10(3) km(2) area within the seasonal sea ice cover was virtually free of winter sea ice. This feature, the Weddell Polynya, was created as sea ice formation was inhibited by ocean convection that injected relatively warm deep water into the surface layer. Though smaller, less persistent polynyas associated with topographically induced upwelling at Maud Rise frequently form in the area, there has not been a reoccurrence of the Weddell Polynya since 1976. Archived observations of the surface layer salinity within the Weddell gyre suggest that the Weddell Polynya may have been induced by a prolonged period of negative Southern Annular Mode (SAM). During negative SAM the Weddell Sea experiences colder and drier atmospheric conditions, making for a saltier surface layer with reduced pycnocline stability. This condition enables Maud Rise upwelling to trigger sustained deep-reaching convection associated with the polynya. Since the late 1970s SAM has been close to neutral or in a positive state, resulting in warmer, wetter conditions over the Weddell Sea, forestalling repeat of the Weddell Polynya. A contributing factor to the Weddell Polynya initiation may have been a La Nina condition, which is associated with increased winter sea ice formation in the polynya area. If the surface layer is made sufficiently salty due to a prolonged negative SAM period, perhaps aided by La Nina, then Maud Rise upwelling meets with positive feedback, triggering convection, and a winter persistent Weddell Polynya.

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URL  <Go to ISI>://000247159300014
DOI  Doi 10.1175/Jcli4046.1