Articles | Volume 13, issue 2
Ocean Sci., 13, 349–363, 2017

Special issue: Climate–carbon–cryosphere interactions in the...

Ocean Sci., 13, 349–363, 2017

Research article 27 Apr 2017

Research article | 27 Apr 2017

Shelf–Basin interaction along the East Siberian Sea

Leif G. Anderson1, Göran Björk1, Ola Holby2, Sara Jutterström3, Carl Magnus Mörth4, Matt O'Regan4, Christof Pearce4,5, Igor Semiletov6,7,8, Christian Stranne4,10, Tim Stöven1,9, Toste Tanhua9, Adam Ulfsbo1,11, and Martin Jakobsson4 Leif G. Anderson et al.
  • 1Department of Marine Sciences, University of Gothenburg, P.O. Box 461, 40530 Gothenburg, Sweden
  • 2Department of Environmental and Energy Systems, Karlstad University, 651 88 Karlstad, Sweden
  • 3IVL Swedish Environmental Research Institute, Box 530 21, 400 14 Gothenburg, Sweden
  • 4Department of Geological Sciences, Stockholm University, 106 91 Stockholm, Sweden
  • 5Department of Geoscience, Aarhus University, Aarhus, Denmark
  • 6International Arctic Research Center, University Alaska Fairbanks, Fairbanks, AK 99775, USA
  • 7Pacific Oceanological Institute, Russian Academy of Sciences Far Eastern Branch, Vladivostok 690041, Russia
  • 8The National Research Tomsk Polytechnic University, Tomsk, Russia
  • 9Helmholtz Centre for Ocean Research Kiel, GEOMAR, Kiel, Germany
  • 10Center for Coastal and Ocean Mapping/Joint Hydrographic Center, Durham, NH 03824, USA
  • 11Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC 27704, USA

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.

Short summary
We use data collected in 2014 to show that the outflow of nutrient-rich water occurs much further to the west than has been reported in the past. We suggest that this is due to much less summer sea-ice coverage in the northwestern East Siberian Sea than in the past decades. Further, our data support a more complicated flow pattern in the region where the Mendeleev Ridge reaches the shelf compared to the general cyclonic circulation within the individual basins as suggested historically.