Shelf invading low oxygen waters control Cenozoic organic carbon burial rates

Rosalind Emily Mayors Rickaby, Thomas J Wood, Zunli Lu, Christian J Bjerrum

The thermostatic mechanisms of Earth’s persistent habitability are far from resolved. High resolution C isotope records, with P accumulation and coarse fraction I/Ca over the Cenozoic, allow the recalculation and assessment of controls on the global proportional flux of organic carbon burial, a regulator of atmospheric CO2 and O2. Proportional Corg burial was suppressed during the hothouse of the Eocene, coincident with an oxygenated water column and low water column phosphate. With decreased sealevel, the area for efficient organic carbon burial diminished, leading increasingly to greater water column phosphate, higher primary productivity and emergent water column de-oxygenation. The influence of sealevel on the areal extent of high sedimentation inner shelf regions acts as a control on phosphate availability for new production, respiratory demand and ocean oxygenation, as proposed by Bjerrum et al., 2006 (1). During intermediate sea-level highs of the Paleocene, and Neogene, pulses of organic carbon burial prevailed for multi-million years, in response to the redox recycling of phosphate when oxygen minimum zones with O2 < ~ 80 µmol/kg were present. A self-limiting intermediate sea-level sweet spot may exist for peak Corg burial due to redox recycling of phosphate, whereby OMZ waters with O2 < 80 µmol/kg impinge on the most Corg rich sediments of the continental shelf. This sweet spot has increasingly narrowed over Earth history due to the deepening OMZs stabilising both atmospheric O2 and CO2. Continental marine inundation controls on phosphate availability, and the sedimentary carbon flux, provide an inevitable positive feedback on the waxing and waning of ice sheets.
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