Shelf-invading low-oxygen waters control Cenozoic organic carbon burial rates.

The thermostatic mechanisms of Earth's persistent habitability remain unresolved. High-resolution Cenozoic C isotope records, P accumulation, and coarse-fraction I/Ca allow recalculation and assessment of controls on the global proportion of total carbon buried as organic carbon (forg), a regulator of atmospheric CO2 and O2. forg was suppressed during the Eocene hothouse, coincident with an oxygenated water column and low water-column phosphate. With decreased sea level, the area for efficient organic carbon and phosphate sedimentary burial diminished, leading increasingly to greater water-column phosphate, higher primary productivity, and emergent water column deoxygenation. The sea-level influence on the areal extent of high sedimentation in shelf regions acts as a control on phosphate availability for new production, respiratory demand, and ocean oxygenation, as proposed by hypsographic models [C. J. Bjerrum, J. Bendtsen, J. J. F. Legarth, Geochem. Geophys. Geosys. 7, 1-24 (2006)]. During intermediate sea-level highs of the Neogene, pulses of enhanced organic carbon burial prevailed for multimillion years, in response to the redox recycling of phosphate when oxygen minimum zones with O2