Foraminiferal I/Ca ratios: Ocean O2 change during the Common Era in Santa Barbara Basin, CA

Elemental composition of marine sediments has been used to reconstruct ocean O₂ (redox) changes through time, with implications for the observed decline in modern ocean O₂. Where most paleo-redox proxies record the transition from oxygen depleted (suboxic) to oxygen deficient (anoxic) conditions, the iodine to calcium ratio (I/Ca) in foraminiferal calcite is unique as it records the transition from well- to poorly-oxygenated water. The standard reduction potential for IO₃^- to I^- is very near that of O₂ to H₂O, and because IO₃^- is the only form of inorganic iodine incorporated into the calcite lattice, foraminiferal calcite I/Ca is a capable proxy for recording the shift from oxic to suboxic conditions. To extend water column O₂ data beyond the instrumental record, benthic and planktonic foraminifera from SPR0901-06KC (34°16.914 N, 120°02.419 W; 591 m water depth) Santa Barbara Basin, California, were analyzed for their I/Ca ratios to generate a paleo-redox reconstruction of the Common Era. Here we present the response of the I/Ca proxy to a variety of climate/ocean conditions as this reconstruction includes the well-ventilated interval at 1840 CE (Macoma event), the Little Ice Age, and the Medieval Climate Anomaly: These intervals represent time periods where the Southern Californian Oxygen Minimum Zone potentially expanded or contracted in response to temperature-driven changes in gas solubility and/or marine productivity changes in the water column accompanied by sediment oxygen demand.