A cosmogenic nuclide-derived chronology of pre-Last Glacial Cycle glaciations during MIS 8 and MIS 6 in northern Patagonia
<p>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...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-01-01
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| Series: | Climate of the Past |
| Online Access: | https://cp.copernicus.org/articles/19/35/2023/cp-19-35-2023.pdf |
| Summary: | <p>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 contribute to knowledge on the topic of
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 the Antarctic Circumpolar Current coupled to them. It is essential to better constrain former shifts
in these circulation mechanisms 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
<span class="inline-formula"><sup>10</sup></span>Be and <span class="inline-formula"><sup>26</sup></span>Al exposure ages from pre-Last Glacial Cycle moraine
boulder, glaciofluvial outwash cobble, and bedrock samples. This dataset
constitutes the first direct chronology dating pre-Last Glacial Maximum (LGM) glacier advances in
northern Patagonia and completes our effort to date the entire preserved
moraine record of the Río Corcovado valley system (43<span class="inline-formula"><sup>∘</sup></span> S,
71<span class="inline-formula"><sup>∘</sup></span> W). We find that the outermost margins of the study site depict at
least three distinct pre-Last Glacial Cycle stadials occurring around
290–270, 270–245, and 130–150 ka. Combined with the local LGM
chronology, we discover that a minimum of four distinct Pleistocene stadials
occurred during Marine Isotope Stages 8, 6, and 2 in northern
Patagonia. Evidence for Marine Isotope Stage 4 and 3 deposits were
not found at the study site. This may illustrate former longitudinal and
latitudinal asynchronies in the Patagonian Ice Sheet mass balance during these
Marine Isotope Stages. We find that 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 the exploration of
the potential roles of seasonality and seasonal duration in driving the southern
mid-latitude ice-sheet mass balance, and they facilitate novel
glacio-geomorphological interpretations for the study region. They also
provide empirical constraints on former ice-sheet extent and dynamics that
are essential for calibrating numerical ice-sheet and glacial isostatic
adjustment models.</p> |
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| ISSN: | 1814-9324 1814-9332 |