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UCL Home  /  Geography  /  News & Events  /  News  /  News Archive  /  February 2010  /  The hydrological cycle and the bi-polar climate see-saw

The hydrological cycle and the bi-polar climate see-saw

Publication in Nature Geoscience of recent research results

The hydrological cycle and the bi-polar climate see-saw

Professor Chronis Tzedakis and Dr Vasiliki Margari are members of a group of scientists whose latest research on climate variability during the past two glacial periods has recently been published in Nature Geoscience.

The intense and abrupt climate swings characteristic of the last glacial period are believed to have arisen from iceberg discharges into the North Atlantic, disrupting the ocean circulation system transporting heat from low latitudes to the North Atlantic. The result was a sharp cooling in the North Atlantic and warming in the South Atlantic, slowly communicated to Antarctica via the Southern Ocean.  This mechanism for asymmetrical climate change across the hemispheres has been called ‘the thermal bipolar see-saw’.  Evidence from ice-core and marine records for the last glacial period and climate models has supported this bipolar seesaw process, but the extent to which its operation is affected by climate conditions and the hydrological cycle remains unclear.  This new study, published in February’s Nature Geoscience, shows that the bipolar see-saw was a feature of the penultimate glacial period, but that its operation was also modified by the background climate state.

The group used marine fossils and pollen grains from rapidly accumulating marine sediments on the Portuguese Margin to create records of North Atlantic sea-surface temperatures, deep-ocean circulation and southern European vegetation. These have extended our perspective on North Atlantic climate variability beyond the current limit of the Greenland ice cores into the penultimate glacial period. This was characterized by different climate conditions and iceberg releases compared with the last glacial period. The analyses suggest that an intensified hydrological cycle may have increased the susceptibility of the Atlantic ocean circulation to iceberg discharges and thus affected the operation of the bipolar see-saw.

The study was conducted by Vasiliki Margari (UCL), Chronis Tzedakis (UCL), Luke Skinner, Maryline Vautravers and the late Professor Sir Nicholas Shackleton (University of Cambridge), and Andrey Ganopolski (Potsdam Institute for Climate Impact Research).


  • Margari, V., Skinner, L.C., Tzedakis, P.C., Ganopolski, A., Vautravers, M. & Shackleton, N.J. (2010) The nature of millennial-scale climate variability during the past two glacial periods. Nature Geoscience 3, 127-133, doi:10.1038/NGEO740


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