The recovery of very high-resolution records of climate variability from the polar ice-sheets, lakes, speleothems and high sedimentation-rate marine sediments has fundamentally changed our perspective on global climate change by revealing the existence of very rapid and intense climate changes in the past. Such records serve to underline the fact that significant climatic transitions may arise from the interaction of parameters that are completely internal to the climate system, emphasizing the importance of feedbacks in the climate system.
One key aspect of the abrupt climate variability recorded during past glacial periods is its ‘bi-polar’ pattern, with abrupt climate swings in the North Atlantic region coincident with more gradual and subdued changes over Antarctica (see figure above). The canonical explanation for this inter-hemispheric coupling is the ‘bipolar seesaw’ mechanism, whereby changes in the strength of the Atlantic overturning circulation result in changes in the interhemispheric heat transport. A sudden reduction of the overturning circulation in the North Atlantic (triggered by a massive iceberg/freshwater release for example) is thus thought to result in a reduction in the northward heat transport to the Northern Hemisphere and a concomitant increase in the southward heat transport to the Southern Hemisphere. The transport of this ‘excess’ heat across the Southern Ocean to Antarctica is presumed to take some time, hence the slower response of Antarctica. The bipolar seesaw mechanism is a neat and highly explanatory theory. It builds on ideas of hysteresis and bi-stabilty in the overturning circulation. However, much remains to be learned about how well this theory fits with reality, what it tells us about the stability of the ocean circulation, and how its behaviour might depend on background climate conditions and/or the character of forcing applied. Current research is looking at the response of the tropical- and North Atlantic, and the Southern Ocean, to these abrupt climate swings, as well as the existence and character of rapid climate change during different climatic regimes, including interglacial (warm) climates like today’s.
Gottschalk, Julia and Skinner, Luke C. and Lippold, Jörg and Vogel, Hendrik and Frank, Norbert and Jaccard, Samuel L. and Waelbroeck, Claire (2016) Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes. Nature Communications, 7. p. 11539. ISSN 2041-1723 DOI 10.1038/ncomms11539
Gottschalk, Julia and Skinner, Luke C. and Misra, Sambuddha and Waelbroeck, Claire and Meenviel, Laurie and Timmermann, Axel (2015) Abrupt changes in the southern extent of North Atlantic Deep Water during Dansgaard–Oeschger events. Nature Geoscience, 8. pp. 950-954. ISSN 1752-0894 EISSN:1752-0908 DOI 10.1038/ngeo2558
Gottschalk, Julia and Skinner, Luke C. and Waelbroeck, Claire (2015) Contribution of seasonal sub-Antarctic surface water variability to millennial-scale changes in atmospheric CO2 over the last deglaciation and Marine Isotope Stage 3. Earth and Planetary Science Letters, 411. pp. 87-99. ISSN 0012821X DOI 10.1016/j.epsl.2014.11.051
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