Organic carbon accumulation rates in the Holocene and glacial Arabian Sea: implications for O2-consumption in the deep-sea and atmospheric CO2 variations

Abstract

Variations in the deep-sea carbon reservoir have been invoked to explain the observed atmospheric carbon dioxide (CO2) changes during glacial-interglacial cycles. In order to distinguish between the quantity of organic matter remineralized in the deep-sea and that permanently removed into sediments, we compared the bulk- and organic carbon-accumulation rates in Holocene and glacial sediments deposited below the oxygen minimum layer with total- and organic carbon fluxes to the deep Arabian Sea from continuous sediment trap deployments. This comparison shows that the mass of organic carbon remineralized at the sediment water interface is mainly a function of the bulk sediment flux. The oxygen consumed by the organic carbon remineralization is of the order of the observed oxygen deficiency of the modern deep Arabian Sea water. We use the evidence from the northern Indian Ocean to speculate on the possible effect of abiogenic mineral flux on the removal of organic carbon from upper layers of the world ocean to the deep-sea. We assume that if the bulk accumulation rate (not primary productivity) influences the flux of organic carbon (that is fixed from the atmosphere by marine organisms), then mineral matter flux will exert a significant control over atmospheric CO2 contents. Model calculations incorporating transient changes in global bulk flux, caused by natural or anthropogenic changes, show that significant proportions of the observed changes in atmospheric CO2 contents can be explained by this mechanism.