Abstract:
Deep ocean carbonate ion concentration is intimately linked to ocean processes that regulate atmospheric CO (sub 2) over glacial time scales. Well dated records of CaCO (sub 3) preservation in deep-sea sediments provide valuable clues about these processes. Building upon previous studies of CaCO (sub 3) preservation in Cape Basin sediments [1, 2], we find that (super 230) Th-normalized fluxes of CaCO (sub 3) are well correlated with the abundance of CaCO (sub 3) during the last glacial period (LGP), allowing us to use the entire record of ODP-1089 CaCO (sub 3) content [1] to infer changes in deep water carbonate ion concentration. During the LGP, peaks in CaCO (sub 3) preservation exhibit features that are reminescant of warm intervals in Antarctic ice cores. Initially we linked increased CaCO (sub 3) preservation to ventilation of deep waters via the Southern Ocean, which increased during Antarctic warm periods [3]. However, precise dating of Cape Basin sediments revealed that CaCO (sub 3) preservation peaks are associated with vigorous North Atlantic Deep Water (NADW) formation following the Antarctic warm periods rather than by ventilation from the Southern Ocean during these warm periods [2]. Thus, the link between deepwater formation and atmospheric CO (sub 2) is complicated by the complementary impacts of ventilation at opposite ends of the earth. Millennial scale features in the CaCO (sub 3) record of the Cape Basin are also observed in North Pacific sediments during the LGP, indicating the widespread impact of NADW formation on deepwater carbonate ion concentration. Finally, we also find an intriguing correlation over longer time scales to suggest that precession forcing [4] and millennial events share some common impacts on deep water carbonate ion via NADW formation. [1] Hodell et al. (2001) Earth. Planet. Sci. Lett. 192, 109-124. [2] Barker et al. (2010) Nature Geosci. 3, 567-571. [3] Anderson et al. (2009) Science 323, 1443-1448. [4] Lisiecki et al. (2008) Nature 456, 85-88.