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The nature of millennial-scale climate variability during the past two glacial periods


During the last glacial period, iceberg discharges into the North Atlantic disrupted the meridional overturning circulation, leading to cooling in the Northern Hemisphere and warming in Antarctica1,2. This asymmetric response can be explained by a bipolar see-saw mechanism3,4,5, whereby changes in the strength of the meridional overturning circulation lead to changes in the interhemispheric heat transport. It is unclear, however, to what extent the response of the overturning circulation is a function of freshwater flux and boundary climate conditions4. Here we use foraminiferal isotope and pollen records from the Portuguese margin to reconstruct surface- and deep-water hydrography and atmospheric changes during the last and penultimate glacial periods. When we compare our records with temperature reconstructions from Antarctica6, we find that the bipolar see-saw was a characteristic feature of both glacial periods. However, the comparison also underlines the dependence of the bipolar see-saw on background climate and magnitude of iceberg discharge. It also suggests that an intensified hydrological cycle may lead to a weaker overturning circulation with a smaller disruption threshold and extended North Atlantic stadial durations.

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Figure 1: Palaeoclimatic data sets over the interval 132–185 kyr BP.
Figure 2: Comparison of last and penultimate glacial characteristics.
Figure 3: Comparison of the character of millennial-scale variability during MIS3 and MIS6.
Figure 4: Amplitude of Antarctic warmings versus duration of North Atlantic stadials during the last and penultimate glacials.


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We remain overwhelmed by the loss of N.J.S., who provided the inspiration for this project. We thank J. McManus, L. de Abreu, B. Martrat and J. Grimalt for discussions and published data, and J. Corr, M. Hall and V. Rennie for technical support. Financial support was provided by NERC (NE/C514758/1), EU (EV K2-CT-2000-00089) and the Royal Society.

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Authors and Affiliations



N.J.S. initiated the project and generated the benthic isotope record. M.V. generated planktonic isotope data. A.G. provided model simulations and conceptual advice. P.C.T. supervised the project. L.C.S. generated extra planktonic and benthic isotope data. V.M. generated the pollen record. V.M., L.C.S., A.G. and P.C.T. wrote the paper. All authors contributed to the interpretation of the results.

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Correspondence to V. Margari, P. C. Tzedakis or N. J. Shackleton.

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The authors declare no competing financial interests.

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Margari, V., Skinner, L., Tzedakis, P. et al. The nature of millennial-scale climate variability during the past two glacial periods. Nature Geosci 3, 127–131 (2010).

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