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Increased productivity in the subantarctic ocean during Heinrich events


Massive iceberg discharges from the Northern Hemisphere ice sheets, ‘Heinrich events’, coincided with the coldest periods of the last ice age1. There is widespread evidence for Heinrich events and their profound impact on the climate and circulation of the North Atlantic Ocean, but their influence beyond that region remains uncertain1. Here we use a combination of molecular fingerprints of algal productivity and radioisotope tracers of sedimentation to document eight periods of increased productivity in the subpolar Southern Ocean during the past 70,000 years that occurred within 1,000–2,000 years of a Northern Hemisphere Heinrich event. We discuss possible causes for such a link, including increased supply of iron from upwelling and increased stratification during the growing season, which imply an alteration of the global ocean circulation during Heinrich events. The mechanisms linking North Atlantic iceberg discharges with subantarctic productivity remain unclear at this point. We suggest that understanding how the Southern Ocean was altered during these extreme climate perturbations is critical to understanding the role of the ocean in climate change.

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Figure 1: Subantarctic productivity changes during Heinrich events.

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Discussions with C. Wunsch, J. Marshall, M. Follows, E. Boyle and P. Parekh contributed to this manuscript. Samples from core MD97-2120 were provided by K. Pahnke and R. Zahn. The Lamont-Doherty Earth Observatory core repository provided samples from core TN057-21-PC2. D. Dryer, M. Fleisher, Y. Chang and M. Bryan assisted with laboratory analyses. Funding for J.P.S. was from the Gary Comer Foundation, the Jeptha H. and Emily V. Wade Award for Research, and a Henry L. and Grace Doherty Professorship. Funding for R.F.A. was from a grants/cooperative agreement from the National Oceanic and Atmospheric Administration.

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Correspondence to Julian P. Sachs.

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Sachs, J., Anderson, R. Increased productivity in the subantarctic ocean during Heinrich events. Nature 434, 1118–1121 (2005).

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