Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 2 6 2006 10.5194/cpd-2-1371-2006 http://www.clim-past-discuss.net/2/1371/2006/ http://www.clim-past-discuss.net/2/1371/2006/cpd-2-1371-2006.html http://www.clim-past-discuss.net/2/1371/2006/cpd-2-1371-2006.pdf 1371 1386 2006-12-20 Application of sediment core modelling to understanding climates of the past: An example from glacial-interglacial changes in Southern Ocean silica cycling A. Ridgwell andy@seao2.org School of Geographical Sciences, University of Bristol, Bristol, UK Paleoceanographic evidence from the Southern Ocean reveals an apparent stark meridional divide in biogeochemical dynamics associated with the glacial-interglacial cycles of the late Neogene. South of the present-day position of the Antarctic Polar Front biogenic opal is generally much more abundant in sediments during interglacials compared to glacials. To the north, an anti-phased relationship is observed, with maximum opal abundance instead occurring during glacials. This antagonistic response of sedimentary properties is an important model validation target for testing hypotheses of glacial-interglacial change, particularly with respect to understanding the causes of the variability in atmospheric CO₂. Here, I illustrate a time-dependent modelling approach to helping understand past climatic change by means of the generation of synthetic sediment core records. I find a close match between model-predicted and observed down-core changes in sedimentary opal content is achieved when changes in seasonal sea-ice extent is imposed, suggesting that the cryosphere is probably the primary driver of the striking features exhibited by the paleoceanographic record of this region. 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