Abstract
Abstract. We identify and map chains of esker beads (series of aligned mounds) up to 15 m high and on average ∼ 65 m wide in central Nunavut, Canada, from the high-resolution (2 m) ArcticDEM. Based on the close 1 : 1 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 8.1 and 6.8 cal kyr 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 from conduits 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 that the prevalence of esker beads across this predominantly marine-terminating sector of the Laurentide Ice Sheet is a result of sediment fluxes that were unable to backfill conduits at a rate faster than ice-margin retreat. Conversely, we hypothesise that esker ridges 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.
Highlights
Eskers record the former channelised drainage of meltwater under ice sheets
Over 5000 esker ridge segments and 4700 esker beads were mapped across the study area, which together form a coherent esker and meltwater channel pattern converging into proto-Hudson Bay (Fig. 1)
Our mapping revealed nearly 5000 esker beads, which because of their association with De Geer moraines are interpreted as quasi-annual ice-marginal deposits formed timetransgressively at the mouth of subglacial conduits during deglaciation
Summary
Eskers record the former channelised drainage of meltwater under ice sheets. They typically comprise a slightly sinuous ridge of glaciofluvial sediments tens to hundreds of metres wide and metres to tens of metres high and are widespread across the beds of the Laurentide and Fennoscandian ice sheets (e.g. Prest et al, 1968; Aylsworth and Shilts, 1989; Boulton et al, 2001; Storrar et al, 2013; Stroeven et al, 2016). Eskers record the former channelised drainage of meltwater under ice sheets They typically comprise a slightly sinuous ridge of glaciofluvial sediments tens to hundreds of metres wide and metres to tens of metres high and are widespread across the beds of the Laurentide and Fennoscandian ice sheets Detailed sedimentological investigations have improved our understanding of the processes and context of esker bead deposition, what we can learn from such time-transgressive records about the past conditions of subglacial channelised drainage remains poorly understood. This includes the factors determining synchronous vs incremental formation of esker ridges, palaeo-ice-margin retreat rates, and subglacial conduit sediment fluxes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
