Orbital Influences on Deep Ocean Oxygen Concentrations and Respired Carbon Storage

Abstract

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 with important implications for climate over Quaternary glacial-interglacial cycles. Here, we present new geochemical data sets from Ocean Discovery Program Site 1240 in the eastern equatorial Pacific to constrain paleoproductivity (Ba_xs flux) and BWO using a multiproxy approach (aU, Mn/Al, Δδ¹³C, and U/Ba). This combination of approaches allows us to quantitatively identify changes in BWO and to parse local and basin-wide contributions to the signal. We find that upwelling, not dust input, is responsible for driving productivity changes at the site. Changes in local carbon export are not the primary driver of changes in BWO, which instead reflect basin-wide changes driven by processes in the Southern Ocean. Our BWO results provide direct evidence for the role of orbital precession and obliquity in driving deep sea respired carbon and oxygen concentrations. We find variations in BWO on the order of ∼50 μmol/kg that occur with ∼23 kyr periodicity 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.