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

2006; Nature Portfolio; Volume: 440; Issue: 7083 Linguagem: Inglês

10.1038/nature04614

1476-4687

Eric Wolff, Hubertus Fischer, Felix Fundel, Urs Ruth, Birthe Twarloh, Geneviève C Littot, Robert Mulvaney, Regine Röthlisberger, M. de Angelis, Claude F. Boutron, Margareta Hansson, Ulf Jonsell, M. A. Hutterli, Fabrice Lambert, P. Kaufmann, B. Stauffer, Thomas F. Stocker, J. P. Steffensen, Matthias Bigler, M.‐L. Siggaard‐Andersen, R. Udisti, Silvia Becagli, E. Castellano, Mirko Severi, Dietmar Wagenbach, Carlo Barbante, Paolo Gabrielli, Vania Gaspari,

Marine and coastal ecosystems

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. At over 3 km long, the ice core drilled at Dome C in Antarctica represents a record of 740,000 years, or eight glacial cycles. This will be the longest climate record available for years to come, so information gleaned from it will become a benchmark for Antarctic climate research. An examination of the core shows that sea ice around Antarctica waxed and waned in line with temperature over multimillennial timescales, but less so over shorter periods. During cold periods, larger amounts of dust were produced from a drier Patagonia, landing in the Southern Ocean where they probably affected marine productivity. Oceanic production of sulphur compounds, which might affect cloud nucleation, was remarkably constant throughout the period. Data from the Southern Ocean sea-ice extent, the biological productivity of the ocean, and atmospheric iron flux over the past eight glacial cycles indicate that during glacial terminations, changes in Patagonia apparently preceded Antarctic sea-ice reduction — showing that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations.