Sedimentary and micropaleontological response to Mid Holocene sudden sea-level falls in Buenos Aires coast: a paleoclimatic perspective.

LAPRIDA, C., COMPAGNUCCI, R., GARCÍA, N. AND VIOLANTE, R.A.

Mendoza, Argentina

Simposio; Reconstructing Past regional Climate Variations in South America over the Late Holocene: a new PAGES intiative.; 2006

PAGES

A sedimentary core from 12.8 mwd at 36º45?43?S - 56º37?13?W reveals the Mid-Holocene history of the northern argentine inner shelf. We reconstructed paleoenvironmental changes and paleo-sea-level trends from 6000 to 3000 yr BP using benthic foraminifera. Our primary evidence strongly supports two secondary, high-frequency sea level (SL) falls reflected by two pulses of mud deposition in the shoreface toe. Paleosalinities reached maximum values at ~5500 yr BP and thereafter declined continuously to modern values, whereas paleoproductivity decreased strongly during SL fall. We compare the timing of these Mid-Holocene SL oscillations with the decadal-scale periodicity observed in a proxy record of solar variability, the sunspot number reconstructed by Solanski et al (2004, 2005), and with atmospheric concentration considering Taylor Dome geochemistry series (Grootes et al., 1994, 1999). During the time elapsed by the core, two intervals of unussually low sun activity occurred, whereas concentration increases quasi-monotonally. This allows to infer that the two episodes of sudden SL fall are related with an abrupt climatic change to cooler and probably drier conditions contemporary of a decrease in solar irradiance. This two successive episodes of SL fall coincide with climatic cooling and/or changes in moisture conditions in various regions of both hemispheres, and corresponds to the onset of the Neoglaciation.