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

Journal article

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 < 90 µmol/kg were present. We propose the existence of a self-limiting intermediate sea-level sweet spot with peak Corg burial due to redox recycling of phosphate, whereby oxygen minimum zones (OMZ) with O2 < 90 µmol/kg impinge on the most Corg rich continental shelf sediments. Such a sweet spot has narrowed over Earth history due to deepening OMZs, stabilizing both atmospheric O2 and CO2. Continental marine inundation controls on phosphate availability, and the sedimentary carbon flux, provide a positive-feedback and rectifier to perturbations during inception of the icehouse world.

Authors: Rickaby, REM; Wood, TJ; Lu, Z; Bjerrum, CJ

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: National Academy of Sciences
• Journal: Proceedings of the National Academy of Sciences
• Volume: 123
• Issue: 26
• Article number: e2526409123
• Publication date: 2026-06-22
• Acceptance date: 2026-04-21
• DOI: 10.1073/pnas.2526409123
• EISSN: 1091-6490
• ISSN: 0027-8424
• Language: English
• Keywords: oxygen minimum zone; phosphate; carbon isotopes; sea level; carbon cycle