Laurentide ice sheet thinning and erosive regimes at Mount Washington, New Hampshire, inferred from multiple cosmogenic nuclides
Published:April 07, 2021
Alexandria J. Koester*, Jeremy D. Shakun, Paul R. Bierman, P. Thompson Davis, Lee B. Corbett, Brent M. Goehring, Anthony C. Vickers, Susan R. Zimmerman, 2021. "Laurentide ice sheet thinning and erosive regimes at Mount Washington, New Hampshire, inferred from multiple cosmogenic nuclides", Untangling the Quaternary Period—A Legacy of Stephen C. Porter, Richard B. Waitt, Glenn D. Thackray, Alan R. Gillespie
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The northward retreat history of the Laurentide ice sheet through the lowlands of the northeastern United States during the last deglaciation is well constrained, but its vertical thinning history is less well known because of the lack of direct constraints on ice thickness through time and space. In addition, the highest elevations in New England are characterized by gently sloping upland surfaces and weathered block fields, features with an uncertain history. To better constrain ice-sheet history in this area and its relationship to alpine geomorphology, we present 20 new 10Be and seven in situ 14C cosmogenic nuclide measurements along an elevation transect at Mount Washington, New Hampshire, the highest mountain in the northeastern United States (1917 m above sea level [a.s.l.]). Our results suggest substantially different exposure and erosion histories on the upper and lower parts of the mountain. Above 1600 m a.s.l., 10Be and in situ 14C measurements are consistent with upper reaches of the mountain deglaciating by 18 ka. However, some 10Be ages are up to several times greater than the age of the last deglaciation, consistent with weakly erosive, cold-based ice that did not deeply erode preglacial surfaces. Below 1600 m a.s.l., 10Be ages are indistinguishable over a nearly 900 m range in elevation and imply rapid ice-surface lowering ca. 14.1 ± 1.1 ka (1 standard deviation; n = 9). This shift from slow thinning early in the deglaciation on the upper part of the mountain to abrupt thinning across the lower elevations coincided with accelerated ice-margin retreat through the region recorded by Connecticut River valley varve records during the Bølling interstadial. The Mount Washington cosmogenic nuclide vertical transect and the Connecticut River valley varve record, along with other New England cosmogenic nuclide records, suggest rapid ice-volume loss in the interior northeastern United States in response to Bølling warming.
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Untangling the Quaternary Period—A Legacy of Stephen C. Porter
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Stephen C. Porter was an international leader in Quaternary science for several decades, having worked on most of the world’s continents and having led international organizations and a prominent interdisciplinary journal. His work influenced many individuals, and he played an essential role in linking Chinese Quaternary science with the broader international scientific community. This volume brings together nineteen papers of interdisciplinary Quaternary science honoring Porter. Special Paper 548 features papers from six continents, on wide-ranging topics including glaciation, paleoecology, landscape evolution, megafloods, and loess. The topical and geographical range of the papers, as well as their interdisciplinary nature, honor Porter’s distinct approach to Quaternary science and leadership that influences the field to this day.