Geological Society of America

T111 Mountain Glaciation and Climate Change of the Past and Present II

Monday, 11 October 2021
1:30 PM - 5:30 PM
D139/D140

HOLOCENE GLACIER LENGTH VARIATIONS ALONG THE AMERICAN CORDILLERAS FROM PAIRED 14C-10BE MEASUREMENTS

Paper number: T111-4
Program: Technical Sessions
Time: 2:05 PM – 2:20 PM

Authors

Shaun Marcott
University of Wisconsin-Madison, Madison, WI
Emilio Mateo
Ohio State University, Columbus, OH
Bryan Mark
Ohio State University, Columbus, OH
Brian Menounos
University of Northern British Columbia, Prince George, BC
Donald Rodbell
Union College, Schenectady, NY
Maximillian Van Wyk de Vries
University of Minnesota, Minneapolis, MN
Andrew Wickert
University of Minnesota, Minneapolis, MN
Andrew Jones Presenting Author
University of Wisconsin-Madison, Madison, WI
Andrew Gorin
Boston College, Chestnut Hill, MA
Tori M. Kennedy
Tulane University, New Orleans, LA
Brent M. Goehring
Tulane University, New Orleans, LA
Jeremy D. Shakun
Boston College, Chestnut Hill, MA
Gordon Bromley
National University of Ireland, Galway
Andrew Hein
The University of Edinburgh, Edinburgh
Vincent Jomelli
Université Paris Panthéon-Sorbonne, Meudon

Abstract

Rising temperatures in the industrial era have led to the smallest observed global glacier lengths since record keeping began roughly a century ago. The decline of worldwide alpine glaciation poses a significant societal challenge, most notably in locations reliant on summer glacier melt for agriculture and drinking water. The degree to which modern glacial positions across the globe are anomalous relative to the Holocene, however, remains largely unknown despite a geologic perspective providing insight into future changes. Here, we present 65 paired cosmogenic in situ 14C and 10Be measurements in recently exposed proglacial bedrock for 11 glaciers spanning the length of the American Cordilleras to assess Holocene alpine glacier lengths.

We collected 5-10 bedrock samples at or near the modern front of each glacier. 10Be exposure ages are inferred to represent cumulative exposure durations during the Holocene, while 14C is used to infer burial, as 14C will experience significant decay relative to 10Be when the bedrock is shielded from nuclide production by overlying ice. Because nuclide concentrations can only provide cumulative exposure and burial durations, observed 14C/10Be ratios were compared to outputs from 100,000 randomized exposure-burial histories through a Monte-Carlo-based model to determine when glaciers may have advanced or retreated during the Holocene. Nuclide concentrations are near zero for all four tropical glaciers, a glacier in the Sierra Nevada, California, and a glacier in Patagonia, Chile, providing evidence that these glaciers have retreated to their smallest positions of the Holocene. Other sites in the Northern and Southern hemispheres (30-60º) exhibit a more complex pattern of glacial position through the Holocene, likely reflecting both local and global scale climate forcings.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-367713

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