Late Glacial and Early Holocene cyclic changes in paleowind conditions and lake levels inferred from diatom assemblage shifts in Laguna Potrok Aike sediments (southern Patagonia, Argentina)

摘要

PASADO is a multidisciplinary Potrok Aike Sediment Archive Drilling prOject, which was conducted from 2008 to 2013, focusing on the sedimentary record of the volcanic crater maar Laguna PotrokAike (52 degrees S, 70 degrees W, 116 m asl) in southern Patagonia, Argentina. It represents one of the few non-glacial and extra-Andean sediment archives studied so far on the continental landmass between subtropical South America and Antarctica that covers the entire Holocene and the Late Glacial. In this study, a high-resolution diatom analysis of the Late Glacial time interval situated between 15.60 and 10.51 ka cal. BP was performed on the PASADO sediment core. This period is of particular interest as it encompasses the Antarctic Cold Reversal (ACR), as well as the Younger Dryas (YD) chronozone. To better refine the variability of environmental and climatic conditions of this Late Glacial time interval, we combined our data with those of a microsedimentological analysis conducted on the same sediments and for the same period to infer changes in lake level and water column stratification. Our study revealed that diatoms are an ideal proxy to complement microsedimentological analyses by providing important independent information on the past limnological dynamics of Laguna Potrok Aike and the paleoclimatic conditions that prevailed during the Late Glacial in the study area and allows a new way of explaining shifts in the position of Southern Hemisphere Westerly Winds (SWW) during the Late Glacial. Peaks of planktonic diatoms, particularly Cyclostephanos patagonicus, correspond to previously detected total organic carbon (TOC), Ca/Si, Ca and Mn peaks and support the hypothesis that relatively high lake levels and weaker SWW have prevailed during the Late Glacial. Moreover, a cyclic pattern, observed both in the biological and geochemical indicators, suggests at least five shifts in the position of the SWW from the beginning of the ACR to the end of the YD. The periodicity of these shifts seems to be related to Antarctic ice-sheet discharge (AID) events in the Scotia Sea that coincide with enhanced iceberg flux from the Antarctic ice-sheet. (C) 2015 Elsevier B.V. All rights reserved.