Australia: The Land Where Time Began

A biography of the Australian continent 

Climate Variability on a Millennial Scale During the 2 past Glacial Periods

The meridional overturning circulation was disrupted by iceberg discharge into the North Atlantic during the last glacial period which led to cooling in the Northern Hemisphere and warming in Antarctica (Hemming, 2004; Blunier et al., 1998). A bipolar see-saw mechanism (Stocker & Johnsen, 2003; Ganopolski & Rhamstorf, 2001; Schmittner & Galbraith, 2008) can explain this asymmetric response, with changes in the interhemisphere heat transport resulting from changes in the strength of the meridional overturning circulation. According to the authors¹ it is not clear to what extent the response of the overturning circulation is a function of the flux of freshwater and boundary climate conditions (Ganopolski & Rhamstorf, 2001). In this study the authors¹ reconstructed the hydrography of surface and deep-water and changes of the atmosphere during the last and penultimate glacial periods, by using records of foraminiferal isotope and pollen from the margin of Portugal. The authors¹ found that when comparing their records with temperature reconstructions from Antarctica (Jouzel et al., 2007) the bipolar see-saw was a characteristic feature of both glacial periods. The dependence on background climate and the magnitude of iceberg discharge on the bipolar see-saw is also underlain by the comparison. It also suggests a weaker overturning circulation with a smaller disruption threshold and, in the North Atlantic, extended durations of stadials, may result from an intensified hydrological cycle.

Sources & Further reading

1. Margari, V., L. C. Skinner, P. C. Tzedakis, A. Ganopolski, M. Vautravers, and N. J. Shackleton. "The Nature of Millennial-Scale Climate Variability During the Past Two Glacial Periods." Nature Geosci 3, no. 2 (02//print 2010): 127-31.