Shelf –Basin exchange along the Laptev – East Siberian Seas

The Siberian Shelf Seas are areas of extensive biogeochemical transformation of organic matter, which in combination with brine production from sea ice formation results in cold bottom water of relatively high salinity and nutrient concentrations, as well as low oxygen and pH levels. Data from the SWERUS-C3 expedition on the icebreaker Oden in July to September 2014 show the distribution of these bottom waters along the Siberian continental margin from about 140 to 180 ^oE. The nutrient maximum water, classically named the Upper Halocline, is absent in the west, over the Lomonosov Ridge. It is clearly seen in the Makarov Basin from about 150 ^oE and becomes more intense further to the east. At the intercept of the Mendeleev Rise and the continental slope the nutrient maximum is still intense, but more vertically distributed. Hence it is also found at higher salinities, up to ~34.5. There are strong indications that this high salinity, high nutrient water is produced on the shelf west of 160 ^oE, and that formation of such water is coupled with substantial sea ice production at the outer continental shelf. Remote sensing data show much more open water than previously during the summer months during the last 10 years in the area north of the New Siberian Islands. East of 170 ^oE the transient tracers show significant less ventilated waters below about 100 m depth, likely an indication of a boundary current steered away from the shelf slope by the Mendeleev Rise.