Oligocene-Miocene Antarctic Continental Weathering Record and Paleoclimatic Implications, Cape Roberts Drilling Project, Ross Sea, Antarctica

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The bulk chemistry of mudrocks in Ross Sea drillcores on the Antarctic inner shelf is re-evaluated to extract records of continental paleotemperatures and ice extent. The chemical index of alteration (CIA) of the sedimentary sequence derived from the composite of the Cape Roberts cores changes in accordance with pCO2 [Pagani, M., Zachos, J.C., Freeman, K.H., Tipple, B., Bohaty, S., 2005. Marked change in atmospheric carbon dioxide concentrations during the Paleogene, Science 309, 600-603]. The (K2O + Na2O)/Al2O3 molar ratio of the mudrocks is used as a mean summer temperature proxy for continental Antarctica and it shows similarities with benthic Mg/Ca temperatures for the Southern Ocean [Billups, K., Schrag, D.P., 2002. Paleotemperatures and ice-volume of the past 27 myr revisited with paired Mg/Ca and stable isotope measurements on benthic foraminifera. Paleoceanography 17. doi 10.1029/2000PA000567]. The ratio is calibrated using intervals with significant pollen assemblages and the temperature proxy enables extrapolation of the paleoclimatic data over a larger portion of the drilled record. The CIA and (K + Na)/Al ratios support a persistent cooling and drying of climate through the Oligocene-Miocene transition. The results reinforce the strong coupling between East Antarctic continental temperatures and ice volume, with deep-sea temperatures and concentrations of atmospheric carbon over long timescales.



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