The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink

• Published in: Nature Communications
• Main Authors: Abelmann, Andrea, Gersonde, Rainer, Knorr, Gregor, Zhang, Xu, Chapligin, Bernhard, Maier, Edith, Esper, Oliver, Friedrichsen, Hans, Lohmann, Gerrit, Meyer, Hanno, Tiedemann, Ralf
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Science and Business Media LLC 2015
• Subjects: General Physics and Astronomy; General Biochemistry, Genetics and Molecular Biology; General Chemistry; Southern Ocean; Sea ice
• Online Access: http://dx.doi.org/10.1038/ncomms9136; http://www.nature.com/articles/ncomms9136.pdf; http://www.nature.com/articles/ncomms9136

Abstract Reduced surface–deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO 2 . However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface–subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring–summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall–winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink.