Eastern Tropical Pacific Paleosalinity Reconstructions During the Last Deglaciation

Abstract:

The eastern tropical Pacific is an important climatic crossroad where the Intertropical Convergence Zone and the El Niño/Southern Oscillation drive seasonal and interannual changes in the regional rainfall patterns. Marine sediment cores indicate that the regional hydrological cycle experienced extreme changes during the last deglaciation, in close relationship with changes in the Atlantic Meridional Overturning Circulation. There is, however, no consensus yet on the timing and geographical extent of those hydrological changes, as the timing of the recorded hydrological changes vary from site to site and depend on the proxy used. We present new hydrogen isotope measurements performed on C_37:2 alkenones from a marine sedimentary sequence collected in the Panama Basin, off the Costa Rican margin. While an increase in δD of about 10 ‰ is recorded at the end of the Heinrich event 1, there is no significant change in δD during the Younger Dryas. A comparison of those data with seawater oxygen isotopic signatures estimated from the same core reveals differences in the way atmospheric circulation is captured by those two proxies. A comparison with alkenone hydrogen isotope measurements performed on a core located along the Columbian Margin demonstrates regional contrasts in the sensitivity of the hydrological cycle during te deglaciation. We will tentatively use jointly these results to build up a climatic scenario capable of explaining those contrasting modes of millenial-scale variability.