Missing organic carbon in Eocene marine sediments: Is metabolism the biological feedback that maintains end‐member climates?

Ocean chemistry is affected by p CO 2 in the atmosphere by increasing the dissolution of solid calcium carbonate and elevating the dissolved inorganic carbon concentrations in seawater. Positive feedbacks between the ocean and atmosphere can maintain high atmospheric p CO 2 and affect global climate. We report evidence for changes in the oceanic carbon cycle from the first high‐quality organic carbon (C org ) data set of Eocene sediments beneath the equatorial Pacific upwelling region (Leg 199 of the Ocean Drilling Program). Eocene C org mass accumulation rates (MARs) are 10 times lower than Holocene rates, even though expected C org MARs estimated from biogenic‐barium MARs (an indicator of biological production) equal or exceed modern fluxes. What happened to the missing C org ? Recent advances in ecology and biochemical kinetics show that the metabolism of nearly all animals, marine and terrestrial, is positively correlated by first principles to environmental temperatures. The approximately 10°C abyssal temperature difference from Eocene to Holocene should have radically reduced pelagic C org burial, as we observe. We propose that higher basal metabolism and nutrient utilization/recycling rates in the Eocene water column and surface sediments precluded C org sediment burial in the pelagic ocean. Increased rates of metabolism, nutrient utilization, and lowered C org sedimentation caused by increased temperature may have acted as a biological feedback to maintain high atmospheric p CO 2 and hothouse climates. Conversely, these same parameters would reverse sign to maintain low p CO 2 when temperatures decrease, thereby maintaining “icehouse” conditions during cold climate regimes.