Short-term dissolution response of pelagic carbonate sediments to the invasion of anthropogenic CO₂: A model study

This study addresses the potential for and the quantification of dissolution of marine calcium carbonate (CaCO₃) sediments occurring on century timescales in response to the invasion of anthropogenic CO ₂.It presents results obtained with the global biogeochemical model PISCES interactively coupled to a global sediment model. The latter represents the principal reactions involved in early diagenesis of biogenic opal, CaCO ₃, and organic matter. The model reproduces observed distributions of core top CaCO₃ content and bottom water carbonate chemistry (e.g., [CO₃^2-]). Starting from the climatological state, a model experiment is carried out according to the standard CMIP scenario of atmospheric pCO₂ increasing at a rate of 1% per year from 286 to 1144 ppm over a 140 year time period. The invasion of anthropogenic CO₂ results in a strong decrease in bottom water [CO₃^2-] reaching-100 μM in areas of deep water formation in the North Atlantic and mode and intermediate water formation in the Southern Hemisphere. The concomitant decrease in calcite saturation state of bottom waters drives the dissolution of CaCO₃. The absolute CaCO₃ content averaged over the top first centimeter decreases by up to 6%, while the change in advection calculated at the base of the bioturbated layer (10 cm) is indicative of net erosion. The predicted changes in bottom water chemistry are discussed in terms of their potential impact on benthic communities.