Preprints
https://doi.org/10.5194/egusphere-2024-241
https://doi.org/10.5194/egusphere-2024-241
01 Feb 2024
 | 01 Feb 2024
Status: this preprint is open for discussion and under review for Climate of the Past (CP).

The Laurentide Ice Sheet in southern New England and New York during and at the end of the Last Glacial Maximum – A cosmogenic-nuclide chronology

Allie Balter-Kennedy, Joerg M. Schaefer, Greg Balco, Meredith A. Kelly, Michael R. Kaplan, Roseanne Schwartz, Bryan Oakley, Nicolás E. Young, Jean Hanley, and Arianna M. Varuolo-Clarke

Abstract. We present 40 new 10Be exposure ages of moraines and other glacial deposits left behind by the southeastern sector of the Laurentide Ice Sheet (LIS) in southern New England and New York, summarize the regional moraine record, and interpret the dataset in the context of previously published deglaciation chronologies. The regional moraine record spans the Last Glacial Maximum (LGM), with the outermost ridge of the terminal complex dating to ~26–25 ka, the innermost ridge of the terminal complex dating to ~22 ka, and a series of smaller recessional limits within ~50 km of the terminal complex dating to ~21–20.5 ka. The chronology generally agrees with independent age constraints from radiocarbon and glacial varves. A few inconsistencies among ages from cosmogenic-nuclide measurements and those from other dating methods are explained by geologic scatter where several bedrock samples and boulders from the outer terminal moraine exhibit nuclide inheritance, while exposure ages on large moraines are likely affected by postdepositional disturbance. The exposure-age chronology places the southeastern sector of the LIS at or near its maximum extent from ~26 to 21 ka, which is broadly consistent with the LGM sea-level lowstand, local and regional temperature indicators, and local summer insolation. The net change in LIS extent represented by this chronology occurred more slowly (<5 to 25 m yr-1) than retreat through the rest of New England, consistent with a slow general rise in insolation and modeled summer temperature. We conclude that the major pulse of LIS deglaciation and accelerated recession, recorded by dated glacial deposits north of the moraines discussed here, did not begin until after atmospheric CO2 increased at ~18 ka, marking the onset of Termination 1.

Allie Balter-Kennedy, Joerg M. Schaefer, Greg Balco, Meredith A. Kelly, Michael R. Kaplan, Roseanne Schwartz, Bryan Oakley, Nicolás E. Young, Jean Hanley, and Arianna M. Varuolo-Clarke

Status: open (until 28 Mar 2024)

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  • RC1: 'Review of The Laurentide Ice Sheet in southern New England and New York during and at the end of the Last Glacial Maximum – A cosmogenic nuclide chronology', Christopher Halsted, 01 Mar 2024 reply
Allie Balter-Kennedy, Joerg M. Schaefer, Greg Balco, Meredith A. Kelly, Michael R. Kaplan, Roseanne Schwartz, Bryan Oakley, Nicolás E. Young, Jean Hanley, and Arianna M. Varuolo-Clarke
Allie Balter-Kennedy, Joerg M. Schaefer, Greg Balco, Meredith A. Kelly, Michael R. Kaplan, Roseanne Schwartz, Bryan Oakley, Nicolás E. Young, Jean Hanley, and Arianna M. Varuolo-Clarke

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Short summary
We date sedimentary deposits indicating the southeastern Laurentide Ice Sheet was at or near its southernmost extent from ~26,000 to 21,000 years ago when sea-level was lowest and other climate records indicate glacial conditions. Slow deglaciation began ~22,000 years ago alongside a slow but steady rise in modeled local summer temperature, but significant deglaciation in the region did not begin until ~18,000 years ago when atmospheric CO2 began to rise, signaling the end of the last ice age.