First year sea ice desalination throughout the entire column after the growth season : Observation and Modelling
Abstract
Arctic sea ice extent and thickness are declining rapidly. This reduction represents also a switch from multiyear ice to an increase in a more seasonally sea ice. The increase in surface of first year sea ice would lead to changes in the interaction with both, the atmosphere and the upper ocean layer. Although there has been increasing interest in first year sea ice dynamics, thermal properties of first year sea ice, through a distinct temperature and salinity profile compared with multiyear sea ice, are still poorly known. In March 2007, two sudden and brief salinity anomalies of up to 0.41 were observed below first year sea ice in the Storfjorden coastal Arctic polynya, in Svalbard archipelago. Analyses, supported by a 1D halo-thermodynamic sea ice model reveal that the first salinity burst was associated to brine convection within the ice, while the second was due to flushing by percolating melt water. The convective episode is remarkable as salt cascaded throughout the entire ice, yielding a massive desalination (>3). Such an abrupt desalination throughout the entire column after the growth season, in relatively warm ice, is remarkable It is shown that convection is controlled by ice porosity and can only occur above a temperature threshold (dependent on ice thickness and salinity) more restrictive than that required for ice permeability. Convection is then driven by the penetration of a cold temperature front within the warm ice. This suggests that young ice looses a substantial fraction of salt in a short episode immediately after the wintertime growth, once warm enough for convection to occur over the entire column. As these are fairly general conditions, this rapid process is likely to hold at larger spatial scales in the Arctic.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.C52B..08J
- Keywords:
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- 0750 CRYOSPHERE / Sea ice;
- 0752 CRYOSPHERE / Polynas;
- 0766 CRYOSPHERE / Thermodynamics;
- 0798 CRYOSPHERE / Modeling