Rapid thinning of the Laurentide Ice Sheet in coastal Maine, USA, during late Heinrich Stadial 1

Abstract

Few data are available to infer the thinning rate of the Laurentide Ice Sheet (LIS) through the last deglaciation, despite its importance for constraining past ice sheet response to climate warming. We measured 31 cosmogenic 10 Be exposure ages in samples collected on coastal mountainsides in Acadia National Park and from the slightly inland Pineo Ridge moraine complex, a ~100-km-long glaciomarine delta, to constrain the timing and rate of LIS thinning and subsequent retreat in coastal Maine. Samples collected along vertical transects in Acadia NationalPark have indistinguishable exposure ages over a 300 m range of elevation, suggesting that rapid, century-scale thinning occurred at 15.2 ± 0.7 ka, similar to the timing of abrupt thinning inferred from cosmogenic exposure ages at Mt. Katahdin in central Maine (Davis et al

Applying the Cosmogenic Nuclide Dipstick Model for Deglaciation of Mt. Washington

“…Glacial dipsticks have been instrumental in constraining the thinning history of ice sheets in Scandinavia (Brook et al, 1996;Goehring et al, 2008), Antarctica (Stone et al, 2003;Ackert et al, 2007;Mackintosh et al, 2007Mackintosh et al, , 2011Johnson et al, 2014), and Greenland (Corbett et al, 2011;Nelson et al, 2014). Strikingly, other than our own recent study at Acadia National Park in Maine (Koester et al, 2017), no major glacial dipsticks have been measured for the Laurentide Ice Sheet (LIS), which was the largest body of ice at the Last Glacial Maximum (LGM), accounting for ~65-90 of the 130 m LGM sea level lowstand . There are only two regions where substantial topographic relief (>1000 m) was uncovered by LIS retreat during the last deglaciation -the mountains of New England and southern Quebec (Fig.…”

“…There is little indication of Heinrich event 1 at the southern margin, except perhaps indirectly, with the modest Chicopee readvance in Massachusetts at 17.3 ka, possibly occurring in response to North Atlantic cooling (Ridge et al, 2012). Coastal Maine, mostly below the marine limit, rapidly deglaciated 15-16 ka Koester et al, 2017;Hall et al, 2017), and the North Charlestown moraines were deposited across central New England just prior to the Bølling warming. Thereafter, and synchronous with MWP-1A, the rate of retreat increased dramatically to ~300 m/year (Fig.…”

“…This well-dated margin record makes the region especially conducive to constraining ice volume changes and understanding ice sheet behavior, if, and only if, the thinning history can be well determined. Koester et al, 2017). Inset figure shows the extent of the LIS at 21 ka and 10 ka (Dyke, 2003).…”

“…Dyke et al, 2004), glacial varves (Ridge, 2004;Ridge et al, 2012), and cosmogenic nuclide dating (Balco et al, 2002;Balco and Schaefer, 2006;Bierman et al, 2015;Bromley et al, 2015;Davis et al, 2015;Corbett et al, 2017;Koester et al, 2017;Hall et al, 2017;Fig. 4).…”

“…In addition, a model of the LIS at the end of the Oldest Dryas (~15 ka) and during the Bølling-Allerød (~14.2 ka) found the surface balance increased during the Bølling , supporting the varve thickness record. As the ice sheet retreated further inland the Pineo Ridge moraine complex in coastal Maine was abandoned around the Bølling Interstadial (14.5 ± 0.7 ka; Koester et al, 2017) followed by the Littleton-Bethlehem moraine, just north of the Presidential Range in northern New Hampshire (13.8 ± 0.7 ka, n = 4; Balco et al, 2009;Thompson et al, 2017), and the Androscoggin moraine in northeastern New Hampshire and western Maine (13.2 ± 0.7 ka, n = 7; Bromley et al, 2015) before retreating further north into Canada.…”