Reconstruction of biogenic flux changes in the equatorial Pacific over a glacial/interglacial cycle

Several studies have indicated that variation in dissolved silica and iron could potentially alter the orgC/CaCO3 rain ratio in particles sinking from the surface to the deep ocean and alter the atmospheric PCO 2 over the span of a glacial/interglacial cycle. To test that hypothesis, several marine cores were analyzed in the light of potential changes in water chemistry carried from the subantarctic to the equatorial Pacific and the subsequent possible biological responses at low latitudes.; Three studies were undertaken. In the first, a direct relationship was found between the water chemistry of the high- and low-latitudes in the Pacific. Changes in the high latitudes are carried northward from the subantartic by intermediate waters into the Equatorial Undercurrent and appear in the eastern equatorial Pacific. In this part of the Pacific basin, there is a clear increase in the rain ratio, concomittant with a likely displacement of the calcite-based planktonic fauna by the silica-based fauna.; The second set of results show the role of the thermocline as a carrier of both temperature and nutrient content changes from the Subantartic zone to the eastern equatorial Pacific during the Holocene onset of the El Nino/ENSO phenomena. Results indicate that the development of ENSO was sensitive to subsurface conditions and driven by extratropical processes.; The third set of results deals with marine biogenic fluxes, the mechanism by which the biotic pump transfers carbon from the atmosphere and upper ocean into the deep-sea reservoir through variations in the ratio of organic carbon to calcite production. Many factors can influence the reconstruction of changes in the rain ratio (i.e., positive or negative trends. Among the most important is the accuracy of the method used to calculate the accumulation of sediments at the seafloor. We examined the influence of chronostratigraphy on two independent methods for calculating mass accumulation rates: traditional sedimentation rate-based estimates versus those based on 230Th normalization. They have given opposite results for the past 30 calendar years in the tropical Pacific. The chronology has been revised after a systematic error was found in previous dating of the glacial to deglacial time interval in the equatorial Pacific. Applying our new chronology to the two approaches on the same set of open-ocean cores shows some convergence, although the magnitude of accumulation rates still remains different.