Ocean Carbon Storage across the middle Miocene: a new interpretation for the Monterey Event

The Miocene Climatic Optimum (MCO, 14–17 Ma) was ~3–4 °C warmer than present, similar to estimates for 2100. Coincident with the MCO is the Monterey positive carbon isotope (δ 13 C) excursion, with oceans more depleted in 12 C relative to 13 C than any time in the past 50 Myrs. The long-standing Monterey Hypothesis uses this excursion to invoke massive marine organic carbon burial and draw-down of atmospheric CO 2 as a cause for the subsequent Miocene Climate Transition and Antarctic glaciation. However, this hypothesis cannot explain the multi-Myr lag between the δ 13 C excursion and global cooling. We use planktic foraminiferal B/Ca, δ 11 B, δ 13 C, and Mg/Ca to reconstruct surface ocean carbonate chemistry and temperature. We propose that the MCO was associated with elevated oceanic dissolved inorganic carbon caused by volcanic degassing, global warming, and sea-level rise. A key negative feedback of this warm climate was the organic carbon burial on drowned continental shelves. In this study, the authors use planktic foraminiferal data to reconstruct ocean carbonate chemistry and temperature from 16.5 to 11 Ma from a size in the tropical eastern Indian Ocean to look at the causes of the Monterey Excursion (ME). They find a positive relationship between dissolved inorganic (DIC) carbon and the ME and a negative one for DIC and the carbon maxima events.