Bentho‐Pelagic Decoupling: The Marine Biological Carbon Pump During Eocene Hyperthermals

Abstract

AbstractFuture environmental change may profoundly affect oceanic ecosystems in a complex way, due to the synergy between rising temperatures, reduction in mixing and upwelling due to enhanced stratification, ocean acidification, and associated biogeochemical dynamics. Changes in primary productivity, in export of organic carbon from the surface ocean, and in remineralization deeper in the water column in the so‐called “twilight zone” may substantially alter the marine biological carbon pump, thus carbon storage in the oceans. We present different proxy records commonly used for reconstructing paleoproductivity, and re‐evaluate their use for understanding dynamic change within and between different constituents of the marine biological pump during transient global warming episodes in the past. Marine pelagic barite records are a proxy for carbon export from the photic and/or mesopelagic zone, and are not positively correlated with benthic foraminiferal proxies for arrival of organic matter to the seafloor over three early Eocene periods of global warming (Ocean Drilling Program Site 1263, SE Atlantic). These two proxies reflect processes in different parts of the water column, thus different components of the biological pump. An increase in temperature‐dependent organic carbon remineralization in the water column would have caused decreased arrival of food at the seafloor, starving the benthic biota and explaining the differences between the proxies, and may have led to ocean deoxygenation. Carbon cycle modeling demonstrates the feasibility of enhanced water‐column remineralization to explain both Site 1263 records, suggesting that this mechanism amplifies pCO2 increase, representing a positive feedback during hyperthermal warming.