Preprints
https://doi.org/10.5194/cp-2022-32
https://doi.org/10.5194/cp-2022-32
 
25 Apr 2022
25 Apr 2022
Status: this preprint is currently under review for the journal CP.

A cosmogenic nuclide-derived chronology of pre-Last Glacial Cycle glaciations during MIS 8 and MIS 6 in northern Patagonia

Tancrède Pierre Marie Leger1, Andrew Steven Hein1, Ángel Rodés2, Robert George Bingham1, Irene Schimmelpfennig3, Derek Fabel2, Pablo Tapia Gonzalez4, and the ASTER Team Tancrède Pierre Marie Leger et al.
  • 1School of GeoSciences, University of Edinburgh, Drummond Street, Edinburgh, EH8 9XP, UK
  • 2Scottish Universities Environmental Research Centre, Scottish Enterprise Technology Park, East Kilbride, G75 OQF, Glasgow, UK
  • 3Aix-Marseille Université, CNRS, Coll. France, IRD, INRAE, CEREGE, Aix en Provence, 13545, France
  • 4Instituto de Geografía, Facultad de Historia, Geografía y Ciencia Política, Pontificia Universidad Católica de Chile, Santiago, Chile
  • A full list of authors appears at the end of the paper.

Abstract. The precise environmental mechanisms controlling Quaternary glacial cycles remain ambiguous. To address this problem, it is critical to better comprehend the drivers of spatio-temporal variability in ice-sheet evolution by establishing reliable chronologies of former outlet-glacier advances. When spanning multiple glacial cycles, such chronologies have the capacity to resolve conundrums on interhemispheric phasing of glaciations and climate events. In southern Argentina, reconstructions of this kind are achievable, as Quaternary expansions of the Patagonian Ice Sheet have emplaced a well-preserved geomorphological record covering several glacial cycles. Moreover, robust ice-sheet reconstructions from Patagonia are powerful barometers of former climate change, as Patagonian glaciers are influenced by the Southern Westerly Winds and its coupled Antarctic Circumpolar Current. Former shifts in these circulation mechanisms are essential to better constrain, as they may have played a critical role in pacing regional and possibly global Quaternary climate change. Here, we present a new set of cosmogenic 10Be and 26Al exposure ages from pre-Last Glacial Cycle moraine boulder, glaciofluvial outwash cobble and bedrock samples. This dataset constitutes the first direct chronology dating pre-LGM glacier advances in northern Patagonia, and completes our effort to date the entire preserved moraine record of the Río Corcovado valley system (43° S, 71° W). We find the outermost margins of the study site depict at least three distinct pre-Last Glacial Cycle glaciations occurring at 284 ± 7 ka, 257 ± 7 ka, and 147 ± 4 ka. Combined with the local LGM chronology, we discover that a minimum of four distinct Pleistocene glaciations occurred during Marine Isotope Stages eight, six, and two in northern Patagonia. Evidence for stage four and three deposits were not found at the study site, which illustrates former longitudinal and latitudinal asynchronies in Patagonian Ice Sheet mass balance during these stages. We find the most extensive middle-to-late Pleistocene expansions of the Patagonian Ice Sheet appear to be out-of-phase with local summer insolation intensity, but synchronous with orbitally-controlled periods of longer and colder winters. Our findings thus enable to explore the potential roles of seasonality and seasonal duration in driving southern mid-latitude ice-sheet mass balance and facilitate novel glacio-geomorphological interpretations for the study region. They also provide empirical constraints of former ice-sheet extent and dynamics that are essential to calibrating numerical ice-sheet and glacial isostatic adjustment models.

Tancrède Pierre Marie Leger et al.

Status: open (until 25 Jun 2022)

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Tancrède Pierre Marie Leger et al.

Tancrède Pierre Marie Leger et al.

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Short summary
Understanding why the past 800 thousand years of Earth’s history has been paced by ~100 thousand-year cycles of alternating cold glacial and warm interglacial conditions remains a major scientific debate. To contribute knowledge to this question, we studied well-preserved glacial deposits in eastern Patagonia. Our work provides a new detailed glacier chronology that enables to establish the timing of multiple Patagonian ice-sheet expansion events over the last three hundred thousand years.