Vertical mixing in the Arctic Ocean inferred from eXpendable Current Profilers

Abstract

Recent and historical data sets from different regions of the Arctic Ocean are analysed using velocity profiles from 127 eXpendable Current Profiler (XCP) deployments from the time period 1993 to 2010. The data sets are processed identically. The shear profiles of horizontal velocity are used to infer vertical mixing. Using the fine-scale parameterization which relate internal wave energy to energy dissipation rate, the diapycnal eddy diffusivity is inferred. An improved version of the fine-scale parameterization which includes corrections for the shear-strain ratio and variation in latitude is also employed. Joint microstructure measurements made it possible to compare the XCP derived eddy diffusivity with direct observations to test the applicability of the parameterization. It is concluded that the skill of the XCP derived eddy diffusivity in the Arctic Ocean is within a factor of 5-6. Using XCP deployments done at the same time and same location the accuracy of the eddy diffusivity calculation is estimated to be within one order of magnitude. The eddy diffusivity values are compared in relation to topographic variations and temporal variability. For the deeper layers of the ocean, the eddy diffusivity values averaged for slope and ridge areas are comparable, and a factor of two higher than those for the abyss. The analysis on the temporal variability was inconclusive due to relatively poor quality data set from 1993.