Dense-water production and overflow from an Arctic coastal polynya in
Storfjorden in winter is a site of active brine formation due to its recurrent polynya. The dense, brine-enriched waters fill the depressions of the fjord to its sill level and subsequently descend like a bottom gravity current, following the topography towards the shelf break. The brine formation a...
| Main Authors: | , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.540.6348 http://folk.uib.no/ngfif/Preprints/Skogseth_etal_AGU05proof.pdf |
| Summary: | Storfjorden in winter is a site of active brine formation due to its recurrent polynya. The dense, brine-enriched waters fill the depressions of the fjord to its sill level and subsequently descend like a bottom gravity current, following the topography towards the shelf break. The brine formation and the overflow show strong interannual variability governed by both local factors, e.g., preconditioning, the rate of ice formation, and polynya location, and large-scale factors, e.g., Barents Sea winter ice cover and large-scale atmospheric circulation in the North Atlantic. An existing polynya and ice production model, making use of satellite images, wind data, and surface hydrography, is applied to winter 2002 and predicts large brine rejection in agreement with observations. Tuning factors for the polynya model obtained from 5 years of observations are used to extend the cal-culations to 33 years back in time. The ice production in 2002 is predicted to be 5.4 standard deviations away from the preceding 4 years ’ mean but still represen-tative for the mean and variability of the decadal scale. The resulting strong over-flow in 2002 is observed at densely spaced hydrographic stations located across its path. Significant entrainment is observed within the first 40 km of the path of the overflow, reducing the density anomaly of the overflow water by 0.18 and increas-ing the cross-sectional area by a factor of 2. The geostrophic shear is found to be partly responsible for the mixing. Farther downstream, entrainment is less signifi-cant. The geostrophic volume transport of the overflow water is approximately constant at ∼0.06 Sv, in agreement with earlier estimates. The model results com-bined with the field data provide a picture of the link between forcing, generation of the source conditions in the basin, and the corresponding overflow. 1 9485.qxd 04/03/05 5:48 PM Page 1 |
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