A new reconstruction of Laurentide Ice Sheet dynamics based on glacial geomorphology and chronological data

Overview

The North American Laurentide Ice Sheet (LIS: Fig. 1) was the largest ice sheet to grow and decay during the last glacial cycle, dominating fluctuations in global sea level. Accurate reconstructions of its extent, volume and dynamics are, therefore, critical to our understanding of glacial-interglacial cycles and the sensitivity of ice sheets to climate change. Knowledge of its deglaciation since the Last Glacial Maximum (LGM) is also required to understand the rates, magnitude and mechanisms of ice sheet decay and associated impacts on sea level, which is relevant to the assessments of the future stability of modern-day ice sheets in Greenland and Antarctica (Kleman and Applegate, 2014; Stokes et al., 2016; Margold et al., 2018). In addition to responding to climate warming during the last deglaciation, the behaviour of the LIS was also capable of driving abrupt climate change through the delivery of meltwater and icebergs that perturbed the climate system (e.g. Barber et al., 1999). More broadly, the configuration and retreat history of the LIS was an important constraint on the migration and dispersal of flora and fauna, including early humans.

Given its size and importance, the LIS is one of the best-studied palaeo-ice sheets and there are numerous papers that have attempted to reconstruct its extent and dynamics using a variety of both empirical and modelling approaches (see review in Stokes, 2017). However, the majority of studies, especially those taking an empirical approach, have tended to focus on specific regions and time periods, and fewer attempts have been made to reconstruct ice sheet dynamics (flow patterns, ice divides, margin retreat, ice streaming) in a coherent manner using a consistent approach.

Building on the last major synthesis over three decades ago (Dyke and Prest, 1987), and drawing on a wealth of new glacial geomorphological and chronological data, the overall aim of this project is to produce a new reconstruction of the LIS from the LGM (~21 ka) through to its final deglaciation (~8 ka).

This aim will be achieved through the following objectives:

(i) Within a GIS framework, combine new mapping from remote sensing products (satellite imagery and DEMs) with previously-published mapping to generate a coherent dataset of the flow-patterns (e.g. flow-sets of glacial lineations) and ice marginal positions (e.g. moraines) associated with the last deglaciation

(ii) Use previously published chronological data to bracket the ages of the flow patterns and ice margin positions from (i) to produce a coherent reconstruction of ice sheet dynamics through time

(iii) Use the reconstruction in (ii) to answer some key questions about the behaviour of the ice sheet during deglaciation, such as:

a. How did different sectors of the ice sheet respond to external forcing during deglaciation?

b. What processes or mechanisms triggered episodes of ice sheet instability and/or rapid retreat (atmospheric v oceanic warming v ice dynamical instabilities)?

c. How did the ice sheet respond to abrupt changes in climate, such as the warming during the Late Glacial Interstadial and the Younger Dryas cold period?

Click on an image to expand

Image Captions

Figure 1: Reconstructed extent of the LIS at 21.8 ka after Dyke & Present (1987) (taken from Stokes, 2017)

Methodology

The aims and objectives will be met through well-established glacial inversion methods (Kleman et al., 1997), whereby the glacial geomorphology on the ice sheet bed is ‘inverted’ to infer the properties of the ice sheet that created it (i.e. the presence of cold versus warm-based ice, ice flow direction and relative speed, presence or absence of meltwater drainage systems, etc.). These methods have been used to produce comprehensive reconstructions of both the Scandinavian Ice Sheet (Kleman et al., 1997) and the British-Irish Ice Sheet (Clark et al., 2012), but not yet for the entire LIS during the last deglaciation.

The first task will be to produce new mapping from satellite imagery and DEMs and then collate this with previously-published mapping to create a new map of the flow-patterns (flow-sets) and ice margin positions of the ice sheet within a GIS framework. The second major task will be to collate previously published chronological data that constrains ice sheet retreat. These chronological data will then be combined with the mapped data to produce a new reconstruction of ice sheet dynamics through time. These methods may be extended to also include the development and evolution of major ice-marginal lakes and there may be opportunities to compare the empirically-derived reconstruction with those derived from numerical modelling (e.g. Tarasov et al., 2012).

Project Timeline

Year 1

Initial literature review; collate previously-published maps and chronological data into a GIS framework; begin mapping of glacial geomorphology using satellite imagery and DEMs

Year 2

Analysis of glacial geomorphological landform assemblages and the compilation of a flow-set map for the entire ice sheet; continued processing of chronological data; begin to build a new ice sheet reconstruction

Year 3

Refine the new ice sheet reconstruction; analyse ice sheet dynamics in the context of changes in the ocean-climate system; compile thesis writing

Year 3.5

Complete the tasks as detailed under Year 3

Training
& Skills

The student will receive training in relevant GIS techniques and software packages, including ArcGIS, and ERDAS imagine. It is anticipated that this training will also be supplemented with specialist subject training (e.g. at the British Society for Geomorphology’s Postgraduate Workshop) and may include internationally-recognised summer schools (e.g. the Karthaus ‘Ice and Climate’ summer school). Broader transferable skills (e.g. communicating science, thesis writing, writing for publication, presentation skills) will be developed through formal training at Durham University. The candidate will also be expected to publish their work and present it at both national and international conferences.

References & further reading

Barber, D.C. et al. (1999) Forcing of the cold event of 8,200 years ago by catastrophic drainage of Laurentide lakes. Nature, 400, 344-348.

Clark, C.D. et al. (2012) Pattern and timing of retreat of the last British-Irish Ice Sheet. Quaternary Science Reviews 44, 112-146.

Dyke, A.S. & Prest, V.K. (1987) Late Wisconsinan and Holocene history of the Laurentide Ice Sheet. Géographie physique et Quaternaire 41, 237-263.

Kleman, J. & Applegate, P.J. (2014) Durations and propagation patterns of ice sheet instability events. Quaternary Science Reviews 92, 32-39.

Kleman, J. et al. (1997) Fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model. Journal of Glaciology 43, 283-299.

Margold, M., Stokes, C.R. and Clark, C.D. (2018) Reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the Laurentide Ice Sheet. Quaternary Science Reviews, 189, 1-30.

Stokes, C.R. (2017) Deglaciation of the Laurentide Ice Sheet from the Last Glacial Maximum. Cuardernos de Investigación Geográfica, 43, 377-428.

Stokes, C.R. et al. (2016). Ice stream activity scaled to ice sheet volume during Laurentide Ice Sheet deglaciation. Nature, 530, 322-326.

Tarasov, L. et al. (2012) A data-calibrated distribution of deglacial chronologies for the North American ice complex from glaciological modeling. Earth and Planetary Science Letters, 315-316, 30-40.

Further Information

Professor Chris R. Stokes, Durham University
Email: c.r.stokes@durham.ac.uk
Tel: +44 (0) 191 334 1955

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