Constraining landscape history and glacial erosivity using paired cosmogenic nuclides in Upernavik, northwest Greenland

Abstract

High-latitude landscape evolution processes have the potential to preserve old, relict surfaces through burial by cold-based, nonerosive glacial ice. To investigate landscape history and age in the high Arctic, we analyzed in situ cosmogenic 10 Be and 26 Al in 33 rocks from Upernavik, northwest Greenland. We sampled adjacent bedrock-boulder pairs along a 100 km transect at elevations up to 1000 m above sea level. Bedrock samples gave signifi cantly older apparent exposure ages than corresponding boulder samples, and minimum limiting ages increased with elevation. Two-isotope calculations ( 26 Al/ 10 Be) on 20 of the 33 samples yielded minimum limiting exposure durations up to 112 k.y., minimum limiting burial durations up to 900 k.y., and minimum limiting total histories up to 990 k.y. The prevalence of 10 Be and 26 Al inherited from previous periods of exposure, especially in bedrock samples at high elevation, indicates that these areas record long and complex surface exposure histories, including signifi cant periods of burial with little subglacial erosion. The long total histories suggest that these highelevation surfaces were largely preserved beneath cold-based, nonerosive ice or snowfi elds for at least the latter half of the Quaternary. Because of high concentrations of inherited nuclides, only the six youngest boulder samples appear to record the timing of ice retreat. These six samples suggest deglaciation of the Upernavik coast at 11.3 ± 0.5 ka (average ± 1 standard deviation). There is no difference in deglaciation age along the 100 km sample transect, indicating that the ice-marginal position retreated rapidly at rates of ~120 m yr −1 .

The Greenland Ice Sheet during the last glacial cycle: Current ice loss and contribution to sea-level rise from a palaeoclimatic perspective

“…Kelly, 1985;Roberts et al, 2009), however, from recent studies (e.g. Corbett et al, 2013;Roberts et al, 2013;Lane et al, 2014;Winsor, 2014;Winsor et al, 2015) it seems likely that most trimlines in Greenland reflect an englacial thermal boundary rather than the LGM ice surface, i.e. that they mark a transition from warm-based ice (below the trimline) to cold-based, non-erosive ice (above the trimline).…”

“…4A), but they stress that this is most probably a minimum scenario, given that some of the deposits may be recessional features formed during retreat of the ice margin rather than when it was at its largest. Other authors have favoured a scenario with more extensive LGM ice cover in this area (Ó Cofaigh et al, 2004;Håkansson et al, 2007Håkansson et al, , 2009, arguing that areas previously interpreted as being ice-free based on weathering limits could rather have been covered by cold based, non-erosive ice during the LGM, an interpretation that seems likely in light of new results from west Greenland (Corbett et al, 2013;Roberts et al, 2013;Lane et al, 2014;Winsor, 2014;Winsor et al, 2015).…”

Constraining multi-stage exposure-burial scenarios for boulders preserved beneath cold-based glacial ice in Thule, northwest Greenland

“…Cold-based ice also existed in mid-latitude regions, especially at high elevations (Bierman 45 et al, 2015) and along thin ice sheet margins (Colgan et al, 2002). Since cosmic rays attenuate 46 as they pass through Earth materials at a rate controlled by density, burial by ~10 m of ice causes 47 production of nuclides by spallation to become negligible (Lal, 1988 1999; Briner et al, 2003;Briner et al, 2006;Corbett et al, 2013;Håkansson et al, 2008;Kaplan 56 et al, 2001;Marquette et al, 2004;Stroeven et al, 2002;Sugden et al, 2005).…”

Guidebook for Field Trips in Western Maine and Northern New Hampshire

“…Although 10 Be inheritance is common in polar landscapes Davis et al, 1999, Marsella et al, 2000Briner et al, 2006;Miller et al, 2006;Corbett et al, 2013Corbett et al, , 2016Margreth et al, 2016), our study is one of the first to suggest that non-erosive, cold-based ice sheets are a factor to be considered in temperate mountainous regions. As suggested in Bierman et al (2015), variable glacial erosion rates between summits and valleys may play a strong role in development and maintenance of northern Appalachian topography through the Quaternary.…”