BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-10-1849-2013 Oxygen and indicators of stress for marine life in multi-model global warming projections Cocco V. 1 2 Joos F. https://orcid.org/0000-0002-9483-6030 1 2 Steinacher M. https://orcid.org/0000-0002-4795-1749 1 2 Frölicher T. L. https://orcid.org/0000-0003-2348-7854 3 Bopp L. 4 Dunne J. 5 Gehlen M. https://orcid.org/0000-0002-9688-0692 4 Heinze C. https://orcid.org/0000-0003-4074-8390 6 7 8 Orr J. https://orcid.org/0000-0002-8707-7080 4 Oschlies A. https://orcid.org/0000-0002-8295-4013 9 Schneider B. 10 Segschneider J. 11 Tjiputra J. https://orcid.org/0000-0002-4600-2453 6 7 8 Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland Oeschger Centre for Climate Change Research, University of Bern, Zähringerstrasse 25, 3012 Bern, Switzerland Atmospheric and Oceanic Sciences Program, Princeton University, Sayre Hall, Forrestal Campus, Princeton, NJ 08544, USA Laboratoire des Sciences du Climat et de l'Environnement (LSCE), L'Orme des Merisiers Bât. 712, 91191 Gif sur Yvette, France Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey 08540, USA Geophysical Institute, University of Bergen, Allégaten 70, 5007 Bergen, Norway Bjerknes Centre for Climate Research, Bergen, Norway, Allégaten 55, 5007 Bergen, Norway Uni Klima, Uni Research, Allégaten 55, 5007 Bergen, Norway Helmholtz Centre for Ocean Research Kiel (GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany Institute of Geosciences, University of Kiel, Ludewig-Meyn-Str. 10, 24098 Kiel, Germany Max-Planck-Institut für Meteorologie, Bundesstrasse 53, 20146 Hamburg, Germany 19 03 2013 10 3 1849 1868 Copyright: © 2013 V. Cocco et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/10/1849/2013/bg-10-1849-2013.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/10/1849/2013/bg-10-1849-2013.pdf

Decadal-to-century scale trends for a range of marine environmental variables in the upper mesopelagic layer (UML, 100–600 m) are investigated using results from seven Earth System Models forced by a high greenhouse gas emission scenario. The models as a class represent the observation-based distribution of oxygen (O<sub>2</sub>) and carbon dioxide (CO<sub>2</sub>), albeit major mismatches between observation-based and simulated values remain for individual models. By year 2100 all models project an increase in SST between 2 °C and 3 °C, and a decrease in the pH and in the saturation state of water with respect to calcium carbonate minerals in the UML. A decrease in the total ocean inventory of dissolved oxygen by 2% to 4% is projected by the range of models. Projected O<sub>2</sub> changes in the UML show a complex pattern with both increasing and decreasing trends reflecting the subtle balance of different competing factors such as circulation, production, remineralization, and temperature changes. Projected changes in the total volume of hypoxic and suboxic waters remain relatively small in all models. A widespread increase of CO<sub>2</sub> in the UML is projected. The median of the CO<sub>2</sub> distribution between 100 and 600m shifts from 0.1–0.2 mol m<sup>&minus;3</sup> in year 1990 to 0.2–0.4 mol m<sup>&minus;3</sup> in year 2100, primarily as a result of the invasion of anthropogenic carbon from the atmosphere. The co-occurrence of changes in a range of environmental variables indicates the need to further investigate their synergistic impacts on marine ecosystems and Earth System feedbacks.

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