Modelling the Marine Carbonate Pump and its Implications on the Atmospheric CO:sub:2:/sub: Concentration

Abstract

The marine carbonate pump includes the production of calcium carbonate, CaCO:sub:3:/sub: by marine organisms and its subsequent transport to depth. The balance between carbonate production in surface waters and dissolution and accumulation in sediments influences the surface water CO:sub:2:/sub: concentration and thus the ocean´s capacity to take up atmospheric CO:sub:2:/sub:.Models are developed to investigate on calcium carbonate dissolution in the oceanic water column. Model results yield that dissolution in zooplankton guts contributes a significant portion of the proposed carbonate loss. Dissolution fueled by the respiration of organic matter in marine snow aggregates is very sensitive to the size and settling velocity of the aggregate, which determines the boundary layer thickness and the stability of an undersaturated microenvironment. The constraints set by field data yield that the chemical gradients between the aggregate and the bulk seawater are too small to enable significant carbonate dissolution. Furthermore, the role of the carbonate pump in regulating atmospheric pCO:sub:2:/sub: on glacial to interglacial timescales is investigated. To this end, a model of calcium carbonate dissolution and accumulation in the marine sediments is developed. The model is used to determine the contribution of the marine carbonate pump on the observed glacial to interglacial shift in atmospheric pCO:sub:2:/sub:. Increased glacial production of organic carbon yields increased carbonate dissolution in the sediments, explaining ca. 30-50 microatm lower pCO:sub:2:/sub: at the Last Glacial Maximum ca. 20,000 years before present, which accounts to approximately half the observed shift. The organic matter production change, however, has to be accompanied by a deepening of the remineralization depth.