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Seasonal evolution of the upper-ocean adjacent to the South Orkney Islands, Southern Ocean: results from a "lazy biological mooring".

Meredith, Michael P.; Nicholls, Keith W.; Renfrew, Ian A.; Boehme, Lars; Biuw, Martin; Fedak, Mike. 2011 Seasonal evolution of the upper-ocean adjacent to the South Orkney Islands, Southern Ocean: results from a "lazy biological mooring". Deep Sea Research II, 58 (13-16). 1569-1579. 10.1016/j.dsr2.2009.07.008

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Abstract/Summary

A serendipitous > 8-month time series of hydrographic properties was obtained from the vicinity of the South Orkney Islands, Southern Ocean, by tagging a southern elephant seal (Mirounga leonine) on Signy Island with a Conductivity-Temperature-Depth/Satellite-Relay Data Logger (CTD-SRDL) in March 2007. Such a time series (including data from the austral autumn and winter) would have been extremely difficult to obtain via other means, and it illustrates with unprecedented temporal resolution the seasonal progression of upper-ocean water mass properties and stratification at this location. Sea ice production values of around 0.15-0.4 m month(-1) for April to July were inferred from the progression of salinity, with significant levels still in September (around 0.2 m month(-1)). However, these values presume that advective processes have negligible effect on the salinity changes observed locally; this presumption is seen to be inappropriate in this case, and it is argued that the ice production rates inferred are better considered as "smeared averages" for the region of the northwestern Weddell Sea upstream from the South Orkneys. The impact of such advective effects is illustrated by contrasting the observed hydrographic series with the output of a one-dimensional model of the upper-ocean forced with local fluxes. It is found that the difference in magnitude between local (modelled) and regional (inferred) ice production is significant, with estimates differing by around a factor of two. A halo of markedly low sea ice concentration around the South Orkneys during the austral winter offers at least a partial explanation for this, since it enabled stronger atmosphere/ocean fluxes to persist and hence stronger ice production to prevail locally compared with the upstream region. The year of data collection was an El Nino year, and it is well-established that this phenomenon can impact strongly on the surface ocean and ice field in this sector of the Southern Ocean, thus the possibility of our time series being atypical cannot be ruled out. Longer-term collection of in situ ocean data from this locality would be desirable, to address issues relating to interannual variability and long-term change.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.dsr2.2009.07.008
Programmes: BAS Programmes > Polar Science for Planet Earth (2009 - ) > Polar Oceans
ISSN: 0967-0645
Additional Keywords: South Orkney Islands, Southern Ocean, Weddell-Scotia Confluence, Upper-ocean seasonality, sea ice production, air-sea-ice interaction, elephant seal
NORA Subject Terms: Marine Sciences
Electronics, Engineering and Technology
Date made live: 31 Aug 2011 15:08
URI: http://nora.nerc.ac.uk/id/eprint/15023

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