1-Main objective:

"To develop a robust geomorphological and geochronological reconstruction of the former Patagonian Ice Sheet behaviour over several Quaternary glacial cycles, in its understudied northeastern sector (43° S)"

2-Study site:

The Río Corcovado and Río Huemul valley systems, formerly host to major outlet glaciers of the Patagonian Ice Sheet (43°S; 71°W).

3-Fieldwork:

2-month and 5-weeks expeditions to study site in 01-02/2019 and 01-02/2020, respectively. Fieldwork was organised and coordinated by Tancrède P.M. Leger, while field investigations and sampling were conducted by Tancrède P.M. Leger, Andrew S. Hein, Robert G. Bingham, and Pablo Tapia Gonzalez.

4-Context:

To the east of the Patagonians Andes, the Argentinian foreland contains one of the most complete and well-preserved sequence of Quaternary glacial deposits in the world (Clapperton, 1993). This unique geomorphic record provides the opportunity to reconstruct and date volume fluctuations of the formerly 2500 km-long Patagonian Ice Sheet over several Quaternary glacial cycles (Mercer, 1976). The ice sheet moreover occupied a key mid-latitude position in the ocean-dominated Southern Hemisphere, as it was the only ice mass to fully intersect the precipitation-bearing southern westerly wind belt. Reconstructing its former expansions can thus provide rare insight into how southern mid-latitude climates evolved during the Quaternary.

5- Questions addressed:

• This investigation aims at resolving questions on the timing of the maximum ice extent of the last glacial cycle (LGC) in northeastern Patagonia as well as older, pre-LGC glaciations, for which few robust glacier chronologies exist in the southern Hemisphere.

• The project addresses long-standing conundrums concerning latitudinal asynchronies in the timing of the Last Glacial Maximum (LGM) and onset of deglaciation across Patagonia, and the complex atmospheric/oceanic processes responsible for such anomalies. Such information can help to determine and differentiate between climatic vs non-climatic drivers of Quaternary glaciations at the southern mid-latitudes.

• The project's geomorphological and geochronological reconstruction provides an empirical benchmarking framework addressing questions regarding the former regional ice-flow direction, palaeolake dynamics, subglacial thermal conditions, and the timing of ice-free environments, all of which are important for improved calibration of numerical ice-sheet models.

• This study also includes the geochronological and surface mass balance modelling reconstruction of small climate-sensitive mountain glaciers in the study area. This work enables addressing questions regarding local evolution of palaeo-temperatures and palaeo-precipitations during the last glacial termination (LGT; ~18 ka), thus tracking the intensity variation and latitudinal migrations of the southern westerly wind belt, an essential component for better understanding Quaternary episodes of sudden global climate change.

6-Methods:

• Detailed glacial geomorphological mapping

• Analysis of remotely-sensed imagery and topographic data

• Glaciogenic, glaciofluvial, glaciolacustrine sedimentological investigations

• Terrestrial cosmogenic nuclide surface exposure dating of:

-Moraine boulders (n = 48 ages): Dates moraine formation event and glacial advances/still-stand

-Palaeo-shoreline surface cobbles (n = 6 ages): Dates shoreline abandonment and former proglacial-lake-level drop: e.g. following drainage re-arrangement events.

-Ice-moulded bedrock (n = 3 ages): Dates glacial retreat from the surface location, or proglacial-lake-level drop below its elevation if formerly covered by water bodies.

-Proglacial outwash surface cobbles (n = 16 ages) : Dates pro-glacial outwash deposition by glacial meltwater runoff, considered time-synchronous to timing of glacial advance/still-stand.

• Bayesian age modelling for statistically correcting exposure-age inconsistencies with stratigraphic order of events.

• Numerical modelling of mountain-glacier advances using a spatially-distributed ice-flow model (SIA physics) coupled with a positive degree-day surface mass balance parameterisation.

• Optically Stimulated Luminescence dating of laminated glaciolacustrine sediment deposits (varves)

7- Results and discussions:

• See PhD's output research articles (n=4) under website "Publications" tab