Chair: Kumiko Azetsu-Scott

Leif Anderson ^(1)*, Ylva Ericson ⁽²⁾, Christoph Humborg ^(3,4), Igor Semiletov ^(5,6,7), Adam Ulfsbo ⁽¹⁾

¹ Department of Marine Sciences, University of Gothenburg, 412 96 Gothenburg, Sweden

² The University Centre in Svalbard, Pb 156, 9171 Longyearbyen, Norway

³ Baltic Nest Institute, Baltic Sea Centre, Stockholm University, 106 91 Stockholm, Sweden

⁴ Department of Applied Environmental Science, Stockholm University, 106 91 Stockholm, Sweden

⁵ International Arctic Research Center, University Alaska Fairbanks, Fairbanks, AK 99775, USA

⁶ Pacific Oceanological Institute, Russian Academy of Sciences Far Eastern Branch, Vladivostok 690041, Russia

⁷ The National Research Tomsk Polytechnic University, Tomsk, Russia

Background
The Siberian Shelf Seas are areas of extensive biogeochemical transformation of organic matter, both of marine and terrestrial origin. This in combination with brine production from sea ice formation results in a cold bottom water of relative high salinity and partial pressure of carbon dioxide (pCO₂). These biochemical processes have a much greater impact on Ocean Acidification than that of anthropogenic CO₂.

Methods
The data presented are from the 2014 SWERUS-C3 expedition along the Siberian shelf break and covers a longitudinal range of around 125 ^oE to 175 ^oW. This presentation is based on the following constituents; Dissolved Inorganic Carbon (DIC), Total Alkalinity (TA), pH, oxygen, nutrients, and salinity. The saturation state of calcium carbonate () as well as pCO₂ was calculated from the combinations of pH-TA and pH-DIC.

Findings
Five sections across the shelf slope showed substantial CO₂ supersaturated waters. The highest pCO₂ was found around 100 m depth at the shelf break, with decreasing levels at the same depth into the deep basins. These waters also had high nutrient and low oxygen concentrations, illustrating microbial decay of organic matter to be the source. Consequently, bottom waters with high pCO₂ (up to more than 1200 µatm) and low  (below 0.5 for aragonite) was formed in the East Siberian Seas through degradation of organic matter.

Conclusions
The corrosive water is exported into the deep Makarov and Canada Basins at a depth range of about 50-150 metres. The salinity ranges between 32-34 and there is a potential for this water to be mixed up to levels where calcifying (aragonite) organisms live, e.g., pteropods. Hence, the conditions projected for the end of this century already occurs in parts of the Arctic Ocean at present.