Abstract
Here we investigate the intensity of eddy generation and their properties in the marginal ice zone (MIZ) regions of Fram Strait and around Svalbard using spaceborne synthetic aperture radar (SAR) data from Envisat ASAR and Sentinel-1 in winter 2007 and 2018. Analysis of 2039 SAR images allowed identifying 4619 eddy signatures. The number of eddies detected per image per kilometer of MIZ length is similar for both years. Submesoscale and small mesoscale eddies dominate with cyclones detected twice more frequently than anticyclones. Eddy diameters range from 1 to 68 km with mean values of 6 km and 12 km over shallow and deep water, respectively. Mean eddy size grows with increasing ice concentration in the MIZ, yet most eddies are detected at the ice edge and where the ice concentration is below 20%. The fraction of sea ice trapped in cyclones (53%) is slightly higher than that in anticyclones (48%). The amount of sea ice trapped by a single ‘mean’ eddy is about 40 km2, while the average horizontal retreat of the ice edge due to eddy-induced ice melt is about 0.2–0.5 km·d–1 ± 0.02 km·d–1. Relation of eddy occurrence to background currents and winds is also discussed.
Highlights
Eddies forming at the ice edge and within marginal ice zones (MIZ) are a common dynamic feature of the ice edge evolution under varying winds and ocean currents in polar oceans
Analysis of spaceborne synthetic aperture radar (SAR) data for two winter periods of 2007 and 2018 allowed identifying 4619 eddy signatures in the MIZ and at the ice edge with 399 eddy signatures detected in December 2006–March 2007, and 4220—in January–April 2018
Apart of MIZ eddies, open-ocean eddies were detected in the data, their number was surprisingly small, only 323 eddy signatures
Summary
Eddies forming at the ice edge and within marginal ice zones (MIZ) are a common dynamic feature of the ice edge evolution under varying winds and ocean currents in polar oceans. They are known to be important for sea ice deformation, horizontal transport and melting. Submesoscale ocean variability induces large vertical velocities bringing warm subsurface waters into the mixed layer and results in pronounced ocean-sea ice heat fluxes localized over cyclonic eddies and filaments reaching about 100 W m−2 [8]. It leads to enhanced mixing of water masses over short horizontal scales, so impacting the sea ice and biological structures within the MIZ [10]
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