Late Pleistocene evolution of the ocean's carbonate system

We demonstrate that the carbonate record from a single site (Ocean Drilling Program Site 1089) in the deep South Atlantic represents a qualitative, hi gh-resolution record of the temporal evolution of the carbonate saturation state of the deep sea. The record is especially notable because it is free from many of the complications that limit other records (low sedimentation rates, blurring by chemical erosion, bioturbation, etc.). The pattern of ca rbonate variability is characteristic of Indo-Pacific cores with high-carbo nate glacials and low-carbonate interglacials. Wt% carbonate lags changes i n benthic delta O-18 by an average of similar to 7.6 kyr, and carbonate var iations are in-phase with the rate of change (first derivative) of benthic delta O-18. Intense dissolution occurs at the transition from interglacial to glacial periods and increased preservation occurs during deglaciations. These observations represent two fundamentally different responses of the m arine carbonate system. The lagged response of carbonate to 6180 reflects a steady-state mass balance process whereby the lysocline adjusts to maintai n alkalinity balance between riverine input and marine burial. The Site 108 9 carbonate signal is remarkably similar to inferred changes in the Sr/Ca o f seawater for the past 250 kyr, which implies that both carbonate dissolut ion and seawater Sr/Ca may be controlled by sea level-induced changes in th e location of carbonate deposition (shelf-basin fractionation) during glaci al to interglacial cycles. The transient change in preservation during the transitions into and out of glacial stages reflects a response of the carbo nate system to a redistribution of alkalinity and DIC in the ocean (i.e. ca rbonate compensation). Comparison of the Site 1089 carbonate and Vostok pCO (2) records suggests a role of deep-sea [CO32-] variations for governing at least some second-order features of the atmospheric pCO, signal. In order to quantify this role, however, measurement of indices of dissolution along a true depth transect. will be required to estimate the magnitudes of chan ges in deep-sea [CO32-]. (C) 2001 Elsevier 3 Science B.V. All rights reserv ed.