Shelf–Basin interaction along the East Siberian Sea

Abstract

Abstract. Extensive biogeochemical transformation of organic matter takes place in the shallow continental shelf seas of Siberia. This, in combination with brine production from sea-ice formation, results in cold bottom waters with relatively high salinity and nutrient concentrations, as well as low oxygen and pH levels. Data from the SWERUS-C3 expedition with icebreaker Oden, from July to September 2014, show the distribution of such nutrient-rich, cold bottom waters along the continental margin from about 140 to 180 • E. The water with maximum nutrient concentration, classically named the upper halocline, is absent over the Lomonosov Ridge at 140 • E, while it appears in the Makarov Basin at 150 • E and intensifies further eastwards. At the intercept between the Mendeleev Ridge and the East Siberian continental shelf slope, the nutrient maximum is still intense, but distributed across a larger depth interval. The nutrient-rich water is found here at salinities of up to ∼ 34.5, i.e. in the water classically named lower halocline. East of 170 • E transient tracers show significantly less ventilated waters below about 150 m water depth. This likely results from a local isolation of waters over the Chukchi Abyssal Plain as the boundary current from the west is steered away from this area by the bathymetry of the Mendeleev Ridge. The water with salinities of ∼ 34.5 has high nutrients and low oxygen concentrations as well as low pH, typically indicating decay of organic matter. A deficit in nitrate relative to phosphate suggests that this process partly occurs under hypoxia. We conclude that the high nutrient water with salinity ∼ 34.5 are formed on the shelf slope in the Mendeleev Ridge region from interior basin water that is trapped for enough time to attain its signature through interaction with the sediment.

On the Variability of Stratification in the Freshwater-Influenced Laptev Sea Region

“…Further, considering that Atlantic water is the main source of nutrients along the Eurasian continental slope, shelf-basin exchange processes may gain importance within the Siberian shelf ecosystem. In addition, it remains an open question how changes in sea ice, brine production, and the eastward progression of the Atlantic water influence will affect the shelf-basin interaction along the continental slope (Anderson et al, 2017;Polyakov et al, 2017;Bluhm et al, 2020).…”

The Pan-Arctic Continental Slope: Sharp Gradients of Physical Processes Affect Pelagic and Benthic Ecosystems

“…Slope angle also appears to govern contrasts in shelf-basin exchange; for example, the basin seaward of the steep Laptev Sea slope shows comparatively little signal of Laptev Sea shelf waters egressing seaward, suggesting that shelf-basin exchange here is constrained. In contrast, further east along the wide East Siberian slope, enhanced transport of shelf waters into the basin is found (Anderson et al, 2017). These exchange windows are particularly relevant near the large rivers, as freshwater is an important contribution for the water column stratification of the Arctic Ocean (Carmack et al, 2016), as discussed further in section "Functions of the Slope: System Connectivity vs.…”

Influence of the bordering shelves on nutrient distribution in the Arctic halocline inferred from water column nitrate isotopes

“…These changes have profound impacts on primary production and upper ocean dynamics, and, therefore, the functioning of the Arctic marine ecosystems (Rainville et al 2011;Wassmann and Reigstad 2011;Yool et al 2015). Primary production has increased by 30% from 1998 to 2012 (Arrigo and van Dijken 2015). Whether this increase in productivity will continue as sea ice declines further, is difficult to predict (Vancoppenolle et al 2013;Arrigo and van Dijken 2015).…”

“…Primary production has increased by 30% from 1998 to 2012 (Arrigo and van Dijken 2015). Whether this increase in productivity will continue as sea ice declines further, is difficult to predict (Vancoppenolle et al 2013;Arrigo and van Dijken 2015). In this respect, the availability of fixed nitrogen (i.e., reactive N or non-N 2 ; also defined as biologically available N) also sets a limit on phytoplankton growth in the Arctic Ocean (Popova et al 2012;Codispoti et al 2013).…”

“…In this respect, the availability of fixed nitrogen (i.e., reactive N or non-N 2 ; also defined as biologically available N) also sets a limit on phytoplankton growth in the Arctic Ocean (Popova et al 2012;Codispoti et al 2013). Current understanding in the N dynamics of Arctic Ocean is limited compared to other ocean regions and reducing these uncertainties would increase the reliability of projections for future Arctic primary productivity (Chang and Devol 2009;Vancoppenolle et al 2013;Arrigo and van Dijken 2015).…”