Reconstructing the ocean carbon system variation during the last 150,000 years according to the Antarctic nutrient hypothesis

Abstract

In this study, the Vostok ice core CO2 record and the δ13C difference between the deep Atlantic and Pacific (δa − δp) are used in combination with model simulations to analyze the history of the ocean carbon pump and the sources of Atlantic deep water during the last 150 kyr. It is assumed that the mechanism by which the glacial atmospheric CO2 decreased is an increase in the ratio of Antarctic net carbon production to upwelling in that region. Results from a wide range of circulations and Antarctic net carbon productions input into a 14‐box ocean‐atmosphere model show that similar distributions of phosphate, δ13C, atmospheric CO2 content and surface versus deep radiocarbon age are produced once the following parameters are fixed: (1) the ratio of net carbon production to upwelling in the Antarctic region, (2) the ratio of Northern Component Water to Antarctic Bottom Water input into the Atlantic, and (3) the total upwelling into the low‐latitude surface waters. Therefore rather arbitrary circulations and Antarctic net production values can be used to map model simulated geochemical properties as a function of these parameters. Decrease in atmospheric CO2 and Atlantic to Pacific δ13C difference are calculated from the model for constant low‐latitude upwelling, and these are mapped as a function of the ratios 1 and 2 above. The isolines of these two geochemical properties tend to be orthogonal, and one can position any ΔpCO2, δa − δp pair on an overlay of the two maps. This is done for coeval ice core CO2 and marine sedimentary δ13C data for the last 150 kyr. One finds that the history of the Antarctic carbon pump efficiency varies with the same pattern as that of the atmospheric CO2. The fraction of Northern Component Water entering the Atlantic tends to vary with the same shape function as the global marine δ18O curve.