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

Climate of the past

article

Tancrède P. M. Leger¹  Andrew S. Hein¹  Ángel Rodés²  Robert G. Bingham¹  Irene Schimmelpfennig³  Derek Fabel²  Pablo Tapia⁴ 

[1]School of GeoSciences, University of Edinburgh

[2]Scottish Universities Environmental Research Centre

[3]Aix-Marseille Université

[4]Instituto de Geografía, Facultad de Historia, Geografía y Ciencia Política, Pontificia Universidad Católica de Chile

DOI  :  10.5194/cp-19-35-2023

学科分类：社会科学、人文和艺术（综合）

来源: Copernicus Publications

【 摘 要 】

The precise environmental mechanisms controllingQuaternary glacial cycles remain ambiguous. To address this problem, it iscritical to better comprehend the drivers of spatio-temporal variability inice-sheet evolution by establishing reliable chronologies of formeroutlet-glacier advances. When spanning multiple glacial cycles, suchchronologies have the capacity to contribute to knowledge on the topic ofinterhemispheric phasing of glaciations and climate events. In southernArgentina, reconstructions of this kind are achievable, as Quaternaryexpansions of the Patagonian Ice Sheet have emplaced a well-preservedgeomorphological record covering several glacial cycles. Moreover, robustice-sheet reconstructions from Patagonia are powerful barometers of formerclimate change, as Patagonian glaciers are influenced by the SouthernWesterly Winds and the Antarctic Circumpolar Current coupled to them. It is essential to better constrain former shiftsin these circulation mechanisms as theymay have played a critical role in pacing regional and possibly globalQuaternary climate change. Here, we present a new set of cosmogenic 10 Be and 26 Al exposure ages from pre-Last Glacial Cycle moraineboulder, glaciofluvial outwash cobble, and bedrock samples. This datasetconstitutes the first direct chronology dating pre-Last Glacial Maximum (LGM) glacier advances innorthern Patagonia and completes our effort to date the entire preservedmoraine record of the Río Corcovado valley system (43 ∘  S,71 ∘  W). We find that the outermost margins of the study site depict atleast three distinct pre-Last Glacial Cycle stadials occurring around290–270, 270–245, and 130–150 ka. Combined with the local LGMchronology, we discover that a minimum of four distinct Pleistocene stadialsoccurred during Marine Isotope Stages 8, 6, and 2 in northernPatagonia. Evidence for Marine Isotope Stage 4 and 3 deposits werenot found at the study site. This may illustrate former longitudinal andlatitudinal asynchronies in the Patagonian Ice Sheet mass balance during theseMarine Isotope Stages. We find that the most extensive middle-to-late Pleistoceneexpansions of the Patagonian Ice Sheet appear to be out of phase with localsummer insolation intensity but synchronous with orbitally controlledperiods of longer and colder winters. Our findings thus enable the exploration ofthe potential roles of seasonality and seasonal duration in driving the southernmid-latitude ice-sheet mass balance, and they facilitate novelglacio-geomorphological interpretations for the study region. They alsoprovide empirical constraints on former ice-sheet extent and dynamics thatare essential for calibrating numerical ice-sheet and glacial isostaticadjustment models.

【 授权许可】

CC BY