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Contribution of Southern Ocean surface-water stratification to low atmospheric CO2 concentrations during the last glacial period

Abstract

The nitrogen-isotope record preserved in Southern Ocean sediments, along with several geochemical tracers for the settling fluxes of biogenic matter, reveals patterns of past nutrient supply to phytoplankton and surface-water stratification in this oceanic region. Areal averaging of these spatial patterns indicates that reduction of the CO2 ‘leak’ from ocean to atmosphere by increased surface-water stratification south of the Polar Front made a greater contribution to the lowering of atmospheric CO2 concentration during the Last Glacial Maximum than did the increased export of organic carbon from surface to deep waters occurring further north.

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Figure 1: Comparison of geochemical data for Holocene and last-glacial timesderived from deep-sea sediment cores.
Figure 2: Difference between last-glacial and Holocene values of geochemical data.
Figure 3: Age dependence of geochemical data from two sediment cores from theIndian sector of the Southern Ocean.
Figure 4: Bulk sediment δ15N.
Figure 5: Changes in export flux, vertical mixing and nutrient utilization inferred for the Atlantic and central Indian sector of the Southern Ocean.

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Correspondence to Roger François.

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François, R., Altabet, M., Yu, EF. et al. Contribution of Southern Ocean surface-water stratification to low atmospheric CO2 concentrations during the last glacial period. Nature 389, 929–935 (1997). https://doi.org/10.1038/40073

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