Drivers of Laptev Sea interannual variability in salinity and temperature.

Eurasian Rivers provide a quarter of total fresh water to the Arctic, maintaining a persistent fresh layer that covers the surface Arctic Ocean. The Lena River supplies the largest volume of runoff and plays a key role in this system, as runoff outflows into the Laptev Sea as a particularly shallow plume. This freshwater export controls Arctic Ocean stratification, circulation, and basin-wide sea ice area. Previous in-situ and modelling studies suggest that local wind forcing is a primary driver of variability in Laptev sea surface salinity (SSS) with no consensus over the roles of Lena river discharge and sea ice cover in contributing to this variability. Until recently, satellite SSS retrievals were insufficiently accurate for use in the Arctic, due to the low sensitivity of the L-band signal they utilise in cold water and challenges of retrieval near sea ice. However, retreating sea ice cover and continuous progress in satellite product development have significantly improved SSS retrievals, giving satellite SSS data true potential in the Arctic. This study demonstrates a novel method of using satellite-based SSS, sea surface temperature (SST) data, in-situ observations, and reanalysis products to identify the dominant drivers of interannual variability in Laptev Sea dynamics. Satellite-based SSS is found to agree well with in-situ data in this region (r > 0.8) and provides notable improvements compared to the reanalysis product used in this study (r > 0.7) in capturing patterns and variability observed in in-situ data. The satellite SSS data firmly establishes what has previously been subject to debate due to the limited years and locations analysed with in-situ data: that the zonal wind is the dominant driver of offshore or onshore Lena river plume transport. This finding is affirmed by the strong agreement in SSS pattern in all reanalyses and satellite products used in this study under eastward and westward wind regimes. The pattern of SST also varies with the zonal wind component, and drives spatial variability in sea ice area. The strong correspondence between large scale and local zonal wind dynamics and the key role of SSS and SST variability in driving sea ice and stratification dynamics demonstrates the importance of changes in large-scale atmospheric dynamics for variability in this region as well as for future Arctic sea ice dynamics and freshwater transport. [ABSTRACT FROM AUTHOR]