Enhanced paleoproductivity across the Oligocene/Miocene boundary as evidenced by benthic foraminiferal accumulation rates

Abstract

The Oligocene to Miocene boundary (23 Ma) marks one of the major Cenozoic cooling steps. A corresponding but slightly lagging δ 13C maximum in benthic foraminifer calcite of globally distributed sediment cores has been attributed to increased organic matter burial, either on land or in the oceans. To test this idea we reconstruct the organic carbon flux to the sea floor at three Atlantic Ocean Drilling Program (ODP) Sites using benthic foraminiferal accumulation rates (BFAR) and compare them with the stable isotope records. Our data show that the δ 18O and δ 13C maximum that characterizes the Oligocene/Miocene boundary is accompanied by a pronounced maximum in BFAR derived paleoproductivity at two of the sites. At tropical Atlantic Site 926 the paleoproductivity increase at the Oligocene/Miocene boundary is smaller than at the higher latitude sites, but high resolution sampling of a 2 million year interval (22–24 Ma) reveals that on eccentricity time scales productivity and stable isotope records are significantly correlated. The productivity records are in phase with the δ 18O and δ 13C records at the short-term (~ 125 ky) component of eccentricity. At the long-term eccentricity period (~ 400 ky) productivity is in phase with δ 18O but leads the δ 13C record by an amount that is consistent with published phase lags between the δ 18O and δ 13C records. These results imply that there was enhanced flux of organic matter to the ocean floor during the O/M climate transition and support that marine primary productivity may have played a role in the carbon cycle and atmospheric CO 2 draw-down at this time.