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

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

Malargüe, Mendoza, Argentina

Simposio; Reconstructing Past regional Climate Variations in South America over the Late Holocene. Simposio Internacional; 2006

A sedimentary core collected from -12.8 m at 36°45´43´´S - 56°37´13´´, Southwest Atlantic, reveals the Mid-Holocene history of the northern argentine shelf. Paleoenvironmental changes and paleo-sea-level trends were reconstructed from 6000 to 3000 years BP using benthic foraminifera. The primary evidence strongly supports two secondary, high-frecuency sea-level falls relfected by two pulses of mud deposition in the shoreface toe. Paleosalinities reached maximum values at 5500 years ago and thereafter declined continuously to modern values, whereas paloproductivity and diversity decreased strongly during se-level falls. The timing of these Mid-Holocene sea-level oscillations was compared with the decadal-scale periodicity observed in a proxy record of solar variability, the sunspot number reconstructed by Solanki et al. (2004, 2005), and with atmospheric CO2 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 CO2 concentration increased quasi-monotonally. This allow us to infer that the two episodes of sudden sea-level fall recognized are related with an abrupt climatic change to cooler and probably drier conditions contemporary of a decrease in solar irradiance. The two succesive episodes of sea-level fall coincide with abrupt increased of sea ice in South Atlantic and climatic cooling and/or changes in moisture conditions in various regions of both hemispheres. This period corresponds to th onset of the Neoglaciation.