Carbon cycle during the last 315,000 years: reconstruction from a marine carbon cycle model

A vertical, one-dimensional marine carbon cycle model, including an atmospheric and a terrestrial biospheric reservoir, is developed. It is used to reconstruct the temporal variations of marine biogeochemical processes, the terrestrial biomass, and the vertical chemical structure during the last 315,000 years from records of the atmospheric carbon dioxide concentration and of the surface and the deepwater δ13C at the Atlantic and Pacific. The obtained range of the difference in the terrestrial biomass between the last glacial maximum (LGM) and present is roughly consistent with previous estimates. The phosphate concentrations in the intermediate and the deepwater were found to vary with almost an opposite phase. No such phase shift was found for the evolutions of total alkalinity and of total dissolved inorganic carbon throughout the glacial–interglacial cycles. This probably reflects the difference between the average remineralization depths of particulate carbonate and organic matter. We also found that the carbon redistribution from the atmosphere and the terrestrial biomass to the ocean occurred in the cold intervals.