Effects of pressure ridge sheltering on the spatial and temporal variability of boundary layer stability under first year sea ice |
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| Institution: | 1. Centers for Disease Control and Prevention, Atlanta, GA, United States of America;2. Massachusetts Department of Public Health, Boston, MA, United States of America;3. ICF, Atlanta, GA, United States of America;1. Center for Geomicrobiology, Department of Bioscience, Aarhus University, Ny Munkegade 114, 8000 Aarhus C, Denmark;2. Center for Microbial Communities, Department of Chemistry and Bioscience, Aalborg University, Aalborg, Denmark;1. BGRIMM Technology Group, Beijing 100160, China;2. Department of Chemistry, City University of Hong Kong, Hong Kong 999077, China |
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| Abstract: | We present series of data describing the small-scale structure of the boundary layer stratification in the vicinity and away from a 1.5 m pressure ridge keel. We then analyze the influence of pressure ridges on the spatial and temporal variability of the ocean boundary layer. Our experiment was done during the melt in order to use small-scale salinity gradients to study the variability in intensity of mixing processes. High-resolution salinity records sampled at 0+, 25 and 50 cm from the ice-water interface were analyzed at two stations, one at 5 m and the other at 75 m from a pressure ridge keel. We observed that, in the immediate vicinity of the ridge, melting is associated with the periodic development and dissipation of a melt layer in relation with the orientation of tidal currents relative to the ridge. In contrast, away from the region under the sheltering influence of the ridge keel, the boundary layer did not show any evidence of stratification during the whole experiment. Data recorded in the vicinity of the ridge are then used to compute eddy diffusivity coefficients for sheltered and non-sheltered events. The observation of a stable melt layer in the vicinity of a ridge keel confirms that pressure ridges drastically modify the dynamics of vertical exchanges in their wake. Besides, our data show a significant spatial and temporal eddy diffusivity variability with a factor 10 between sheltered and non-sheltered areas. Thus, considering that ridges and rubble fields form a substantial fraction of ice-covered areas, our results suggest that effects in their wake may be important in the global budget of ocean-ice exchanges. |
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