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Decline of the marine ecosystem caused by a reduction in the Atlantic overturning circulation


Reorganizations of the Atlantic meridional overturning circulation were associated with large and abrupt climatic changes in the North Atlantic region during the last glacial period1,2,3,4. Projections with climate models suggest that similar reorganizations may also occur in response to anthropogenic global warming5,6,7. Here I use ensemble simulations with a coupled climate–ecosytem model of intermediate complexity to investigate the possible consequences of such disturbances to the marine ecosystem. In the simulations, a disruption of the Atlantic meridional overturning circulation leads to a collapse of the North Atlantic plankton stocks to less than half of their initial biomass, owing to rapid shoaling of winter mixed layers and their associated separation from the deep ocean nutrient reservoir. Globally integrated export production declines by more than 20 per cent owing to reduced upwelling of nutrient-rich deep water and gradual depletion of upper ocean nutrient concentrations. These model results are consistent with the available high-resolution palaeorecord, and suggest that global ocean productivity is sensitive to changes in the Atlantic meridional overturning circulation.

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Figure 1: Time series from the model simulations.
Figure 2: Annual net primary productivity from observations and the ensemble mean of the simulations.
Figure 3: Latitude-depth sections of zonally averaged nitrate concentrations in mmol m-3.
Figure 4: Comparison of simulated changes in export production with palaeoproductivity proxy records.

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Productivity data sets were provided by D. Antoine and W. Gregg. Discussions with A. Oschlies, M. Sarnthein, M. Weinelt and H. Kinkel were appreciated. This research was supported as part of the research unit (Forschergruppe 451) on ocean gateways by the Deutsche Forschungsgemeinschaft (DFG).

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Correspondence to Andreas Schmittner.

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Schmittner, A. Decline of the marine ecosystem caused by a reduction in the Atlantic overturning circulation. Nature 434, 628–633 (2005).

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