Simulation of long eccentricity (400-kyr) cycle in ocean carbon reservoir during Miocene Climate Optimum: Weathering and nutrient response to orbital change

Deep-sea foraminiferal δ<sup>13</sup>C records contain abundant 400-kyr cycles indicating a link between eccentricity forcing and ocean carbon reservoir change. Here we simulate the oceanic δ<sup>13</sup>C maxima events forced by the Earth's orbital geometry during the Miocene Climate Optimum (MCO, 17-14 Ma) using a box model. The simulated results of both surface and deep water δ<sup>13</sup>C display co-varying 400-kyr cycle. Modulated by orbital parameters, weathering induced carbon input will change the burial ratio of carbonates to organic carbon and further result in periodic changes in the oceanic δ<sup>13</sup>C. The increase of riverine nutrient input, which is synchronous with riverine carbon input, often stimulates primary productivity and burial of organic carbon. Our results support that eccentricity maxima (minima) enhance (reduce) weathering intensity and nutrient supply, which lead to minima (maxima) of δ<sup>13</sup>C. The prominent 400-kyr cycle of ocean carbon reservoir is interpreted as likely caused by a long memory of carbon in the ocean.