Orbital Influences on Deep Ocean Oxygen Concentrations and Respired Carbon Storage

Quantitative records of bottom water oxygen (BWO) are critical for understanding deep ocean change through time. Because of the stoichiometric relationship between oxygen and carbon, BWO records provide insight into the physical and biogeochemical processes that control the air-sea partitioning of both gases over Quaternary glacial-interglacial cycles with important implications for climate and benthic habitats. Here, we present new geochemical datasets from Ocean Discovery Program (ODP) Site 1240 in the eastern equatorial Pacific to constrain BWO using a multiproxy approach (aU, Mn/Al, Δδ¹³C, and U/Ba). This combination of approaches, and a co-registered proxy record of the rain rate of organic carbon to the site (Ba_xs flux), allows us to quantitatively identify changes in BWO and to parse local and basin-wide contributions to the signal.

Our results provide direct evidence for the role of orbital precession and obliquity in driving deep sea respired carbon and oxygen concentrations, not just during deglaciations, but during both glacial and interglacial periods. We find variations in BWO on the order of ~50 μmol/kg that occur with ~23 kyr peridiocity during the substages of Marine Isotope Stage 5, and variations of ~100 μmol/kg on glacial-interglacial timescales. These findings have important implications for the role of insolation in driving deep ocean respired oxygen and carbon concentrations and point to physical and biogeochemical changes in the Southern Ocean as key drivers of planetary-scale carbon change.