Quantifying past changes in ocean oxygenation and productivity using carbon isotope gradients in benthic foraminifera

Quantifying oxygen and productivity in the past are critical for understanding deep ocean carbon storage over glacial-interglacial cycles and for developing predictive models linking changes to the carbon cycle with patterns of ocean oxygenation. Most existing paleo-oxygen and paleo-productivity reconstructions are qualitative in nature. However, previous work has shown a quantifiable relationship between oxygen and the 13C/12C difference between the benthic foraminifera species C. wuellerstorfi and G. affinis (Δδ13C) for oxygen levels between 55 and 235 μM. Here we expand this Δδ13C-O2 proxy from 6 cores to over 20 cores in the Atlantic, Pacific and Indian oceans (200 - 3800 meters), finding a similar relationship between bottom water oxygen and carbon isotope systematics. Additionally, we observe a strong relationship between Δδ13C and carbon export flux in regions of high oxygenation (> 235 μM) for 9 cores. Lastly, we employ a modified reaction-transport model of marine sediment diagenesis in order to evaluate the primary controls on the carbon isotope gradients produced during organic matter remineralization at the seafloor.