Marine biological productivity and carbon cycling during the Oligocene to Miocene climate transition

The Oligocene to Miocene boundary marks one of the major Cenozoic cooling steps. A corresponding but slightly out of phase δ13C maximum has been attributed to increased organic matter burial associated with global climate cooling (e.g., Zachos et al., 2001). To test this idea we have constructed records of marine biological productivity (based on benthic foraminiferal accumulation rates, BFAR) and sequestration of total organic carbon (TOC) in pelagic sediments to parallel the stable isotope records from 20-25 Ma. Here we present first results from Ceara Rise Site 926 located in the tropical northwestern Atlantic. Our data show that the δ18O/δ13C maximum that characterized the Oligocene/Miocene boundary is accompanied by a pronounced maximum in BFAR derived paleoproductivity. In addition, there are longer term variations in paleoproductivity that follow the well established eccentricity-scale variations in the δ18O and δ13C record. Cross-spectral analysis focusing on the Oligocene/Miocene boundary interval (22-24 Ma), for which we have an average sampling resolution of about 10 kyr, verifies that paleoproductivity is coherent with the stable isotope records above the 80% level. These results support the hypothesis that there is a relationship between global climate cooling and the carbon cycle via marine primary productivity.