Award: OCE-1220602

At our reconstructed pH levels the surface ocean likely did not become corrosive to calcite during the PETM, consistent with the lack of major extinctions among planktic calcifiers. Furthermore, the PETM onset took at least 4,000 years from which follows that the anthropogenic carbon release rate is unprecedented during the past 66 million years. Planktic foraminifers from a sediment core in the North Pacific (ODP site 1209) show a 30-40% reduction in shell B/Ca at the onset of the event, along with a 0.8 per mil decrease in boron isotopes. These observations are consistent with a significant acidification event lasting at least 70 ky. Timing of the onset and duration of these geochemical anomalies compare favorably with model simulations based on other constraints, with an initial pH drop of ~0.2 to 0.4 units. Moreover, we have now demonstrated that the PETM onset took at least 4,000 years. Our results on carbon input and surface ocean pH changes can be used to understand effects of carbon dioxide emission on future changes in ocean chemistry. Hence they are relevant to the general public and policy makers. Furthermore, the PETM onset took at least 4,000 years from which follows that the anthropogenic carbon release rate is unprecedented during the past 66 million years. This provides a historic/geologic perspective on the current human activities. We suggest that such a 'no-analogue' state represents a fundamental challenge in constraining future climate projections. Also, future ecosystem disruptions are likely to exceed the relatively limited extinctions observed at the PETM. Last Modified: 09/06/2016 Submitted by: Richard E Zeebe