685 / 2024-09-19 02:07:11

Sea ice decline in the eastern Arctic results in expansion of the freshened surface layer

river plume,sea surface salinity,wind forcing,East Siberian Sea,Laptev Sea

In this study, we report anomalously large freshened surface layer in the Eastern Arctic during ice-free season in 2019. This freshened surface layer is formed by river discharge and sea ice meltwater and is also referred as the Lena plume because the Lena River discharge is its major freshwater source. Based on in situ and satellite data, we demonstrate that in August-September 2019 the Lena plume spread from the Lena Delta in the west till the Wrangel Island in the east, i.e., its zonal extent was approximately 2000 km. Area of the Lena plume during this period varied between 550 000 and 850 000 km2, which is 1.5-2 times greater than assessment of its area during previous years, albeit they were often hindered by presence of sea ice coverage. The main reasons for this anomalous spreading of the Lena plume are the following. First, early onset of intense sea ice melting in the Eastern Arctic in 2019 provided significantly greater volume of meltwater inflow to the freshened surface layer, as compared to other years. Second, sea ice cleared out of the Laptev and East Siberian seas by the beginning of August 2019, and these seas remained free of ice during almost three months (longer ice-free period occurred only in 2007 and 2020). Three months of favorable wind forcing on the Lena plume in August-October 2019 caused its anomalously large eastward and northward expansion. The reported expansion of the large Lena plume under favorable sea ice and wind conditions provides the baseline for forecasting the future state of large-scale freshwater cycle in the Arctic Ocean with an expectedly reduced ice cover.