| Summary: | Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Communications 5 (2014): 3107, doi:10.1038/ncomms4107. Today's Sargasso Sea is nutrient-starved, except for episodic upwelling events caused by wind-driven winter mixing and eddies. Enhanced diatom opal burial in Sargasso Sea sediments indicates that silicic acid, a limiting nutrient today, may have been more available in subsurface waters during Heinrich Stadials, the millennial-scale climate perturbations of the last glacial and deglaciation. Here we use the geochemistry of opalforming organisms from different water depths to demonstrate changes in silicic acid supply and utilisation during the most recent Heinrich Stadial. We suggest that during the early phase (17.5-18 ka), wind-driven upwelling replenished silicic acid to the subsurface, resulting in low Si utilisation. By 17ka, stratification reduced the surface silicic acid supply and increased Si utilization efficiency. This abrupt shift in Si cycling would have contributed to high regional carbon export efficiency during the recent Heinrich Stadial, despite being a period of increasing atmospheric CO2. KRH and LFR are funded by US National Science Foundation (USNSF) grant MGG 1029986; KRH is supported by the Climate Change Consortium of Wales (C3W), The Royal Society and a UK NERC New Investigator Grant; LFR is supported by an European Research Council Grant 278705; JFM is funded by US-NSF. 2014-07-23
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