The Life Cycle of the Low Salinity Lenses at the Surface of the Arctic Ocean

In the Arctic Ocean, coherent low salinity anomalies, known as lenses, are often observed at the surface and are thought to result from the input of large amounts of freshwater from sea ice melting and river runoff. In this study, we perform a systematic detection of these lenses and track their displacements in a 21-year simulation performed with a high resolution ocean-sea ice regional model of the Arctic in order to gain a better understanding of their life cycle. Two thirds of the lenses are formed during summer, in response to sea ice melt, river discharge, or are colocated with mesoscale eddies. They are then able to persist for weeks to months, traveling long distance across the basin as their characteristic surface salinity anomalies get eroded through vertical processes. Throughout their life, the lenses are associated with larger sea ice melting flux during summer and concentrate stronger sea ice formation than their surroundings by up to 50%. Over the 21-year period, the number of lenses has increased by $\sim$2%/year over the Arctic Ocean, and the formation locations have shifted following the retreat of the sea ice edge in regions such as Greenland, Barents, and Chukchi seas. Our results suggest that these localized, intermittent and coherent lenses may be important for the large scale Arctic dynamics and the ocean-sea ice interaction.