This 4-year investigation is focused on the dynamics of ocean carbon uptake and sequestration during two early Eocene hyperthermals, with a particular emphasis on the PETM.  This investigation brings together an international team of experts in ocean and carbon cycle modeling, marine and sedimentary geochemistry, and paleoceanography, to jointly address, through data/model comparison, several key questions regarding the nature of the carbon cycle perturbations during these events; 1) What were the mass, rate, and origin of carbon released during the events? 2) What were the rates of sequestration and recovery and what biogeochemical feedbacks came into play? and 3) How did associated extreme changes in ocean carbonate chemistry affect planktonic calcifiers?