Modeling organic carbon burial during sea level rise with reference to the Cretaceous

[ 1] After three decades of research on the correlation between sea level and various proxies, there has been very little quantification of the first-order influence of sea level change on nutrient inventory, marine productivity, and burial of organic carbon. We present a model aimed at quantifying the burial of organic carbon as a function of sea level rise. The biogeochemical model explicitly considers the mean surface area distribution of the Earth as a function of elevation. Also included is dissolved inorganic phosphate ( DIP) liberated from coastal sediments during transgression. We quantify how sea level rise of magnitudes inferred for the mid-Cretaceous influences the phosphorus cycle and burial of organic carbon. The burial efficiency is greater on the shelf. Therefore, in the model, the larger shelf area under high sea level results in more efficient burial of marine organic carbon for a given DIP concentration and associated new production of organic matter (NP). With a Late Cretaceous model shelf area the residence time of DIP decreases by 60% relative to the present- day reference. Thus, in the final steady state, DIP and NP in the open ocean are reduced compared to today when the biologically reactive phosphorus (P-reac) fluxes to the ocean from land are held constant. The lower new production reduces the oxygen demand for respiration and results in a significant oxygenation of the global ocean. Finally, the global organic carbon burial decreases by 30% relative to today in the model. This decrease results from feedbacks between the flux of organic carbon to the seafloor and the ratio of organic carbon to P-reac in buried sediments. In contrast, during sea level rise, coastal erosion may increase the P-reac flux to the ocean by up to similar to 20% relative to today and cause a temporary increase in DIP concentration in the ocean. The resulting increase in organic carbon burial is equivalent to a carbon isotope event of + 0.5 to 1 parts per thousand. Larger carbon isotope events can be triggered by sea level rise only when the ocean is sufficiently close to anoxia in the oxygen minimum zone just prior to the sea level rise.