title: The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink.
abstract: Reduced surface-deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. 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.
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Abelmann
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Gersonde
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.|Cardiff School of Earth and Ocean Sciences, Cardiff, Wales CF10 3AT, UK.
authors.forename: Gregor
authors.initials: G
authors.lastname: Knorr
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Xu
authors.identifier: http://orcid.org/0000-0003-1833-9689
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Chapligin
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Edith
authors.initials: E
authors.lastname: Maier
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Esper
authors.affiliation: Free University of Berlin, Berlin 14195, Germany.
authors.forename: Hans
authors.initials: H
authors.lastname: Friedrichsen
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Gerrit
authors.initials: G
authors.lastname: Lohmann
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Hanno
authors.identifier: http://orcid.org/0000-0003-4129-4706
authors.initials: H
authors.lastname: Meyer
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, Bremerhaven 27568, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Tiedemann