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https://doi.org/10.5194/tc-2019-273
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2019-273
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 20 Dec 2019

Submitted as: research article | 20 Dec 2019

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This preprint is currently under review for the journal TC.

A quasi-annual record of time-transgressive esker formation: implications for ice sheet reconstruction and subglacial hydrology

Stephen J. Livingstone1, Emma L. M. Lewington1, Chris D. Clark1, Robert D. Storrar2, Andrew J. Sole1, Isabelle McMartin3, Nico Dewald1, and Felix Ng1 Stephen J. Livingstone et al.
  • 1Department of Geography, University of Sheffield, Sheffield, UK
  • 2Department of the Natural and Built Environment, Sheffield Hallam University, UK
  • 3Geological Survey of Canada, Natural Resources Canada, Ottawa, ON, Canada

Abstract. We identify and map chains of esker beads (series of aligned mounds) up to 15 m high and on average ~ 65 m wide across central Nunavut, Canada from the high-resolution (2 m) ArcticDEM. Based on the close one-to-one association with regularly spaced, sharp crested ridges interpreted as De Geer moraines, we interpret the esker beads to be quasi-annual ice-marginal deposits formed time-transgressively at the mouth of subglacial conduits during deglaciation. Esker beads therefore preserve a high-resolution record of ice-margin retreat and subglacial hydrology. The well-organised beaded esker network implies that subglacial channelised drainage was relatively fixed in space and through time. Downstream esker bead spacing constrains the typical pace of deglaciation in central Nunavut between 7.2 and 6 ka 14C BP to 165–370 m yr−1, although with short periods of more rapid retreat (> 400 m yr−1). Under our time-transgressive interpretation, the lateral spacing of the observed eskers provides a true measure of subglacial conduit spacing for testing mathematical models of subglacial hydrology. Esker beads also record the volume of sediment deposited in each melt season, thus providing a minimum bound on annual sediment fluxes, which is in the range of 103–104 m3 yr−1 in each 6–10 km wide subglacial conduit catchment. We suggest the prevalence of esker beads across this predominantly marine terminating sector of the former Laurentide Ice Sheet is a result of sediment fluxes that were unable to backfill conduits at a rate faster than ice-margin retreat. Esker ridges, conversely, are hypothesised to form when sediment backfilling of the subglacial conduit outpaced retreat resulting in headward esker growth close to but behind the margin. The implication, in accordance with recent modelling results, is that eskers in general record a composite signature of ice-marginal drainage rather than a temporal snapshot of ice-sheet wide subglacial drainage.

Stephen J. Livingstone et al.

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Stephen J. Livingstone et al.

Stephen J. Livingstone et al.

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Short summary
We map series of aligned mounds (esker beads) across central Nunavut, Canada. Mounds are interpreted to have formed roughly annually as sediment carried by subglacial rivers is deposited at the ice margin. Chains of mounds are formed as the ice retreats. This high-resolution (annual) record allows us to constrain the pace of ice retreat, sediment fluxes and the style of drainage through time. In particular, we suggest that eskers in general record a composite signature of ice-marginal drainage.
We map series of aligned mounds (esker beads) across central Nunavut, Canada. Mounds are...
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