Abstract

Carbonate reefs and platforms have accumulated CaCO3 at a rate of 8–9 × 1012 mol/yr over the last few million years. The Holocene rate of shallow water CaCO3 deposition is approximately 17 × 1012 mol/yr. In order for the shallow water CaCO3 flux to maintain its long-term average deposition rate, it must decline to below 8 × 1012 mol/yr during glacial intervals. Shallow water CaCO3 sediments represent a large, dynamic carbon reservoir that rapidly affects the alkalinity of the surface ocean and hence the CO2 content of the atmosphere. Shallow water carbonate deposition, while probably an important constraint on paleoatmospheric CO2 concentrations, can only slightly influence the anthropogenically driven buildup of atmospheric CO2.

Introduction

In order for the record of atmospheric CO2 changes contained in glacial ice (Neftel et al., 1982; Barnola et al., 1987) to reflect changes in the deposition of marine carbonate, shallow water deposition during interglacial intervals must be significantly higher than the long-term average, and the global weathering of near–sea level carbonates must contribute an increased flux of dissolved calcium carbonate (CaCO3) to the oceans during glacial low stands (Milliman, 1974). Review of research on the global Holocene shallow water carbonate flux reveals that the size of the shallow water carbonate reservoir is not well constrained.