Insight on the Arctic Halocline Formation from a Lagrangian Model Analysis

The Arctic halocline, characterized by the coincidence of a strong salinity gradient with cold temperatures, is present in most of the Arctic Ocean, and it plays a key role for the dynamics of this basin. It encompasses a large amount of freshwater, which has the potential to affect to the global thermohaline circulation when released to the North Atlantic. It also acts as a barrier between the sea ice pack at the surface and the warm Atlantic-origin water masses found in the intermediate layer of the Arctic Ocean. The mechanisms behind the formation of the Arctic halocline remain uncertain, although they are thought to be both advective and convective in nature. Observations have pointed out the Arctic shelves as a possible region for the halocline formation, through brine convection and haline convection occurring in this region during the ice formation periods.

Here we investigate the processes at play for the formation of the Arctic halocline and the timescale on which they operate using an original numerical method. A quantitative Lagrangian diagnostic is applied to the 3D outputs of a model historical hindcast performed with the global ocean/sea-ice high resolution DRAKKAR model (12 km resolution in the Arctic Ocean), in order to determine the regions and time periods where and when the halocline is formed. Our results emphasize the role of the Barents Sea and the Arctic shelves for the halocline formation. We also investigate the origin of the large seasonal and interanual variability in halocline formation, which is link to variations in sea ice conditions and atmospheric forcing.