The role of the deep mixing in the Storfjorden shelf water plume

Hydrographic observations in deep Fram Strait evidence a plume of Storfjorden Brine-enriched Shelf Water in 1986, 1988 and 2002. The plume spreads along the continental slope over 600 km away from its formation area and reaches 2000 m depth. The plume is 30 to 80 m thick in the deep layer of Fram Strait; it is almost 0.4 °C warmer and 0.06 more saline than the ambient water. The velocity of the plume, observed by a moored current meter in Fram Strait, is 12.60±4.70 cm s−1 .The hydrographic properties of the plume are used to study entrainment. A streamtube model with four entrainment parameterizations is applied. Two Froude-number dependent parameterizations lead to mixing mostly happening over the shelf break, where the Froude number is large. This is in agreement with the traditional view, but is inconsistent with the observed temperature and salinity of the Storfjorden plume. Therefore further entrainment assumptions (a constant and a volume-dependent entrainment) are tested. The volume-dependent entrainment scheme yields the best representation of entrainment in the Storfjorden plume. Our results emphasize the necessity of strong mixing in the deep layers in Fram Strait to achieve an agreement with observed properties of the plume.