Mid-Holocene strengthening of the Southern westerlies in South America - Sedimentological evidences from Lago Cardiel, Argentina (49 degrees S)

Abstract

The paleoclimatic evolution of southern South America is characterized to a large extent by the behavior (strength and latitudinal position) of the storm tracks of the Southern Westerlies. Our study site, Lago Cardiel (49oS), lies within the modern influence of the Southern Westerlies and, therefore, is ideally located to track the past migrations of these storm tracks. With a coring strategy taking into account the lateral differences in sedimentation and an excellent core-to-core correlation using tephra layers, a composite sedimentological record of almost 25 m was established covering the last ~16,000 cal yr. Sedimentological and petrophysical analysis of the cores revealed the establishment of a dominant lake current since 6800 cal yr BP leading to a drift deposition, which is especially well-expressed in the sedimentary record by an increase in magnetic susceptibility values. As this pattern of currents is most likely induced by wind activity, we propose that the observed increase in magnetic susceptibility documents an intensification of the westerly storm tracks. This intensification occurred slightly earlier than previously suggested based on palynological evidence. The strengthening in the Southern Westerlies during the mid-Holocene is most likely caused by an increase in the temperature gradient as a result of enhanced influence and/or southward migration of the Southeast Pacific anticyclone and a larger Antarctic sea-ice extent.