Neogene burial of organic carbon in the global ocean.

Organic carbon buried in marine sediment serves as a net sink for atmospheric carbon dioxide and a source of oxygen 1,2 . The rate of organic carbon burial through geologic history is conventionally established by using the mass balance between inorganic and organic carbon, each with distinct carbon isotopic values (δ 13 C) 3,4 . This method is complicated by large uncertainties, however, and has not been tested with organic carbon accumulation data 5,6 . Here we report a 'bottom-up' approach for calculating the rate of organic carbon burial that is independent from mass balance calculations. We use data from 81 globally distributed sites to establish the history of organic carbon burial during the Neogene (roughly 23-3 Ma). Our results show larger spatiotemporal variability of organic carbon burial than previously estimated 7-9 . Globally, the burial rate is high towards the early Miocene and Pliocene and lowest during the mid-Miocene, with the latter period characterized by the lowest ratio of organic-to-carbonate burial rates. This is in contrast to earlier work that interpreted enriched carbonate 13 C values of the mid-Miocene as massive organic carbon burial (that is, the Monterey Hypothesis) 10,11 . Suppressed organic carbon burial during the warm mid-Miocene is probably related to temperature-dependent bacterial degradation of organic matter 12,13 , suggesting that the organic carbon cycle acted as positive feedback of past global warming.