IAP-24-046

Late Glacial and Holocene glacier dynamics in southeast Alaska / British Columbia

Background and Rationale:

The melt of Alaskan icefields is accelerating (Davies et al., 2024), and will continue to dominate glacier contributions to sea-level rise for decades to centuries (Edwards et al., 2021). However, the historical record of glacier fluctuations in Alaska is particularly sparse; projections of glacier change across Alaska are hampered by the short observational period and by the region comprising several climatic states. We therefore need better records of past ice behaviour, ideally across different climatic states, to calibrate numerical models and improve projections.

There are relatively few studies of past glacier dynamics in southeast Alaska/British Columbia through the Late Glacial and Holocene (Palacios et al., 2020). During the Younger Dryas (12,800 – 11,700 years ago), glaciers around the North Atlantic region advanced substantially. The extent of the Alaskan glacier readvance is unclear (Young et al., 2019). During this time, the region was populated by indigenous peoples, but the interaction between them and the glaciers is poorly understood (Madsen, 2015). This is important, as ice and proglacial lakes may have blocked settlement routes and coastal access. Furthermore, while repeated early, mid and late Holocene neoglaciations have been reconstructed from moraines in other regions of the USA (Marcott et al., 2019), Alaska (Barclay et al., 2009; Davies et al., 2024) and South America (Carrivick et al., 2024), Holocene neoglaciations are poorly constrained in southeast Alaska. Constraining ice dynamics during the Late Glacial and Holocene is critical for understanding global teleconnections and the impact of regional climate events. Finally, temperatures during the Holocene Climatic Optimum may have been warmer than today and could be analogous to the near future. Constraining patterns of glacier loss during such periods could contextualise current change and shed light upon likely future glacier behaviour.

Research questions:

Across southeast Alaska/British Columbia:
1) Is there evidence of ice stabilisation during the Younger Dryas?
2) How did glaciers behave during Holocene neoglaciations and are glaciers now at their minimum extent?
3) What are the glacier-climate sensitivities and internal controls on icefield dynamics?
4) What were the climatic and glaciological conditions during the dated palaeoglacier fluctuations?

Aims and Objectives:

This project will generate new empirical datasets of glacier behaviour in southeast Alaska across multiple climate states, including periods of rapid climate change analogous to the future. These datasets will be used in robust data-model comparisons to help improve forecasting of icefield behaviour.

Objective 1: Compile a geodatabase of published marine, lacustrine and terrestrial geomorphological and chronological datasets across southeast Alaska/British Columbia. Use these datasets to identify areas of poorly known glacier dynamics and to refine the study site location.

Objective 2: Apply geomorphological mapping in the inshore and offshore realm as appropriate to constrain past glacier behaviour at chosen field site.

Objective 3: Apply chronological techniques to constrain the timing of palaeoglacier fluctuations, from marine and lacustrine archives, terrestrial moraines or from nunataks as appropriate.

Objective 4: Reconstruct climatic conditions forcing palaeoglacier fluctuations using numerical ice-flow modelling, forced by palaeoclimate data and global climate model outputs.

Geodatabase:
Review published geomorphological and geochronological data across southeast Alaska, compiling outputs into a geodatabase following established protocols (cf. Batchelor et al., 2019; Davies et al., 2020).

Geomorphological mapping:
Refine the choice of study site and produce a detailed geomorphological map of the study area, using remotely sensed imagery underpinned by fieldwork, to detail the extent of former glacial fluctuations (Chandler et al., 2018). Fieldwork will use drones, sedimentology and geomorphological mapping techniques as appropriate to quantify past glacier dynamics.

Chronostratigraphy:
During fieldwork, apply relative dating techniques and collect rock samples for cosmogenic nuclide sampling, utilising paired isotope analysis where appropriate, from bedrock and from glacially transported boulders, to constrain past glacier fluctuations and rates of thinning (Balco, 2011; Davies, 2021). Collect organic materials for radiocarbon dating from sediment cores or from material embedded within moraines.

Cosmogenic nuclide analysis and radiocarbon ages will be funded by two separate applications to the NERC National Environmental Isotope Facility (NEIF; includes the Radiocarbon Facility and Cosmogenic Isotope Analysis Facility).

Numerical modelling:
Use an open-source numerical ice sheet or glacier model to simulate southeast Alaskan glacier change between the Last Glacial Maximum (LGM) and present. This will include investigation of the growth and decay of LGM ice, constrained by the new database, and any neoglacial regrowth. Using this learning, the modern and future ice evolution will then be simulated, using modern climate reanalysis and ice-core data combined with future scenarios of climate warming.

Year 1

• Review published outputs and compile geodatabase
• Identify target field sites
• Plan fieldwork
• Remotely sensed geomorphological mapping
• Undertake expedition to ground truth remotely sensed mapping and collect chronostratigraphical samples

Year 2

• Application for analysis of cosmogenic / radiocarbon samples
• Preparation and laboratory analysis of samples
• Set up initial modelling experiments and perturbed parameter ensemble modelling
• Presentation of results at national conference

Year 3

• Publication of geomorphological mapping
• Analysis of chronostratigraphical data and application of statistical techniques
• Evaluation of numerical modelling
• Presentation of results at international conference (EGU/AGU)

Year 3.5

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

The student will receive extensive and bespoke training in geomorphological, technical geochronological and numerical modelling skills.