Climatic change and CaCO3 preservation: An 800,000 year bathymetric Reconstruction from the central equatorial Pacific Ocean

Abstract

Sixteen deep‐sea cores from the central equatorial Pacific are used to reconstruct a continuous 800,000‐year (800‐kyr) record of bathymetric variations in carbonate preservation as measured by calcium carbonate (CaCO3) content. The depth of the sedimentary lysocline has fluctuated markedly in conjunction with late Pleistocene climate cycles while the carbonate critical depth (CCrD), which is the water depth where the sediments contain 10% CaCO3, has remained relatively constant. As a result, the depth of the lysocline controls the bathymetric position and thickness of the CaCO3 transition zone, defined as the depth from the lysocline to the CCrD. Modern and interglacial‐aged sediments show poor CaCO3 preservation and thick CaCO3 transition zones. Glacial‐aged sediments show good preservation and deep, thin zones due to the deepening of the lysocline. Detailed comparison of the CaCO3 preservation and oxygen isotope records from the central equatorial Pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages. During the nine major glacial stages of the last 800 kyr, the lysocline deepened by at least 400 to 800 m. This deepening indicates an increase in the abyssal carbonate ion concentration ([CO3=]) and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate‐saturated water mass. The bottom of the transition zone has remained at a relatively constant depth during the Brunhes Chron, indicating a balance between CaCO3 sedimentation and dissolution in the deepest waters of the central equatorial Pacific.