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 (49°S), 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.
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We would like to thank Jorge Moreteau and his crew for the tireless effort to sail on Lago Cardiel under the above-described harsh and windy conditions. We are grateful to Jean Captain, Antoinette Lüdin, Platt Bradbury and Robert Hofmann for assistance in the field, as well as to, Rossana Martini, Rolf Warthmann and Urs Gerber for help in the lab. We thank Valerie Masson-Delmotte and Frank Lamy for the provided data. Comments by F. Lamy, B.L. Valero-Garces and an anonymous reviewer are acknowledged. This study is part of the PATO/PaLaTra project, which is co-founded by the U.S. National Science Foundation grants NSF-EAR-9709145, NSF-ATM-008267 and NSF-ATM-0081279 to V. Markgraf/K. Kelts; and by the Swiss National Science Foundation grants N° 21-50862.97 and N° 20-61704.00/1 to the ETH and University of Geneva limnogeology groups. The authors thank Blackwell Publishing/International Association of Sedimentologists (IAS) for the permission to reproduce Fig. 9 . 14 C analyses were partly performed at the AMS Facility, jointly operated by the Swiss Federal Institute of Technology, Zurich and Paul Scherrer Institute, Villigen, Switzerland. Major element analyses of tephra samples were carried out at the Electron Microprobe facility at the School of GeoSciences, The University of Edinburgh, Scotland.
Copyright 2011 Elsevier B.V., All rights reserved.
- Closed lake basin
- Magnetic susceptibility
- Southern Westerlies
- Wind intensity