Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles

Nature, Vol. 440, No. 23, doi:10.1038/nature04614, 2006

E.W. Wolff, G.C. Littot, R. Mulvaney, R. Röthlisberger and M.A. Hutterli
British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK.
H. Fischer, F. Fundel, U. Ruth and B. Twarlon
Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, D-27568 Bremerhaven, Germany
M. de Angelis and C.F. Boutron
Laboratoire de Glaciologie et Géophysique de l'Environnement, BP96, 38402 St Martin d'Hères cedex, France.
M. Hansson and U. Jonsell
Department of Physical Geography and Quaternary Geology, Stockholm University, 106 91 Stockholm, Sweden.
F. Lambert, P. Kaufmann, B. Stauffer, T.F. Stocker and M. Bigler
Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland.
J.P. Steffensen and M.L. Siggaard-Andersen
Ice and Climate, The Niels Bohr Institute, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark
R. Udisti, S. Becagli, E. Castellano and M. Severi
Department of Chemistry-Analytical Chemistry Section, Scientific Pole-University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Florence, Italy.
D. Wagenbach
Institut für Umweltphysik, University of Heidelberg, INF 229, 69120 Heidelberg, Germany.
C. Barbante and V. Gaspari
Environmental Sciences Department, University of Venice, Calle Larga S. Marta 2137, Italy.
P. Gabrielli
Institute for the Dynamics of Environmental Processes-CNR, University of Venice, I-30123 Venice, Italy.

ABSTRACT.
Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core. These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions. We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales. Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation. We observe large glacial-interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions. During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO₂ increase during glacial terminations. We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000 years ago.