IAP2-23-027

Palaeoglacier and palaeoclimate reconstructions in the Chilean and Argentinian Lake District, Patagonia

Rationale
During past glaciations, the Patagonian Ice Sheet stretched from ~38°S to 55°S, with terrestrial outlet piedmont lobes forming at low elevations above sea level in the northern sector. Reconstruction of the Patagonian Ice Sheet through different and rapidly changing climate states provides insights into past climatic change in a data-sparse area of the globe, forming an important proxy for changes in hemispheric atmospheric and oceanic systems (Davies et al., 2020). This includes insights into the contraction and expansion of the Southern Westerly Winds during significant palaeoclimate transitions; these winds bring moisture and precipitation to the Andes and are a key control on palaeoglaciation (Kaplan et al., 2020; Reynout et al., 2019; Moreno et al. 2014; Leger et al., 2021). Today, these winds are one of the most important climatic controls in the Southern Andes and are driving major changes in ocean currents in West Antarctica. However, large uncertainties in latitudinal extent and long-term dynamics make it challenging to contextualise recent change in this major atmospheric circulation system. Inconsistent model simulations of the past westerly winds with varied predictions for the location of the westerlies (Harrison et al., 2015) challenges our ability to make high-confidence future predictions. Palaeoglacier reconstruction in the northern sector of the former Patagonian Ice Sheet therefore offers opportunities for new insights into past changes in atmospheric and oceanic circulation.

In the Chilean and Argentinian Lake District, in the Valdivia, Bueno and Collon Cura hydrological basins (~39°S), there are small glaciers on volcanoes. However, little is known about the mass balance sensitivities, landsystems and behaviours of these small present-day glaciers, which are likely to be very different from the more well-studied glaciers further south. In this region, there is also limited data on past glacier extent, and chronologies are greatly lacking (Davies et al., 2020). Large piedmont moraines attest to former outlet lobes of the Patagonian Ice Sheet extending to low elevations, but the timing is poorly constrained. Past climate modes, such as the Southern Annular Mode, Antarctic Cold Reversal, Younger Dryas and “Little Ice Age”, may have influenced palaeoglaciers here. Whilst there is growing data on palaeoglacier fluctuations further south (Leger et al., 2020; Martin et al., 2022, Kaplan et al. 2020), Late Glacial and Holocene ice dynamics here in particular have high uncertainty (Davies et al., 2020). This limits our ability to utilise the latitudinal range provided by the former Patagonian Ice Sheet. These glaciers therefore have important and unrealised potentials as proxies for palaeoclimate, bringing insights into large scale climatic reorganisations during different climate states.

Research Questions
Major research questions include,
1) What was the style and manner of the former Patagonian Ice Sheet at ~39°S, and how did this differ from other Patagonian glacial landsystems?
2) What was the timing of the local glacial maximum and palaeoglacier advances in this area?
3) What were the climatic controls forcing palaeoglacier fluctuations?

Aims and Objectives
This project aims to reconstruct the style and manner, timing, and climatic controls on palaeoglacier advances during the Last Glacial Maximum, Late Glacial and Holocene in the Lake District of northern Patagonia.

Objective 1. Apply geomorphological mapping and sediment-landform analyses to constrain past glacier behaviour in east-west transects across the former Patagonian Ice Sheet, prioritising the Valdivia, Bueno and Collon Cura catchments (~39°S).

Objective 2. Apply chronological techniques to constrain the timing of palaeoglacier fluctuations.

Objective 3. Reconstruct the climatic conditions forcing palaeoglacier fluctuations using numerical ice-flow modelling of the glaciers in these catchments, forced by palaeo climate data and GCM outputs.

The student will benefit from participation in the NERC-funded project “Deplete and Retreat: the future of the Andean Water Towers”, gaining experience in collaborating with international partners and with colleagues in other disciplines. They will also benefit from the large international network and knowledge base established within this project.

The student will use remote sensing of satellite imagery and digital elevation models in a Geographical Information System (GIS) to generate initial geomorphological maps, which will be ground truthed and developed in more detail during fieldwork (cf. Leger et al., 2020; Cooper et al., 2021).

Fieldwork will use drones, sedimentology and geomorphological mapping techniques to characterise sediment-landform assemblages. These datasets will be used to generate new glacial landsystems models of palaeoglacier behaviour (cf. Martin et al., 2019).

During fieldwork, the student will collect samples for chronostratigraphical analysis. This could include: organic material from moraines for radiocarbon dating (cf. Anderson et al., 1999); rock samples from boulders on moraines for cosmogenic nuclide exposure-age dating (cf. Balco, 2011); tephrochronology; or analysis of glaciolacustrine varves. See Davies et al., 2020, for more information on these techniques.

Numerical modelling will use the PISM framework set up at Sheffield University and established under ‘Deplete and Retreat’. The student will drive their simulation using high-resolution dynamically downscaled climate models. A perturbed parameter ensemble will be conducted to explore model sensitivity. The best performing models will be identified using model-data comparison tools (e.g. Ely et al., 2021) to create a model-based reconstruction of ice behaviour.

Year 1

• Review of published outputs regarding Patagonian palaeoglaciers;
• Identification of target field sites;
• Remotely sensed geomorphological mapping;
• Planning of first expedition (logistics, permissions);
• Training in chronostratigraphic sample collection and analysis;
• Undertake expedition to ground-truth remotely sensed mapping and collect chronostratigraphical samples;
• Set up initial numerical modelling experiments.

Year 2

• Preparation of application for analysis of radiocarbon / cosmogenic nuclide samples through NEIF;
• Preparation and laboratory analysis of obtained samples;
• Preparation of first publication on glacial geomorphology in study region;
• Perturbed parameter ensemble modelling of target catchment.
• Presentation of initial results at national conference.

Year 3

• Analysis of chronostratigraphic data; application of statistical techniques;
• Reconstruction of palaeoglacier fluctuations;
• Evaluation of numerical modelling of target catchments;
• Preparation of second publication on glacier reconstruction through time;
• Preparation of third publication on insights from numerical modelling;
• Presentation of results at international conference (such as EGU).

Year 3.5

• Complete data analysis, write up of thesis and submission of planned publications.

The student will receive training in a range of chronological techniques and approaches to palaeoglaciology. They will receive bespoke training in numerical modelling, laboratory and field skills, and will receive laboratory training through NERC National Environmental Isotope Geosciences Laboratory (NEIF).

The student will receive the opportunity to attend short courses on numerical ice-flow modelling (e.g. Karthaus) and NERC-recognised courses on topics such as statistics for geosciences.

Further training will be provided through attendance at Quaternary Research Association (QRA) field meetings.