The North Atlantic was a key locus for circulation-driven abrupt climate change in the past and could
play a similar role in the future. Abrupt cold reversals, including the 8.2 ka event, punctuated the
otherwise warm early Holocene in the North Atlantic region and serve as useful paleo examples of rapid
climate change. In this work, we assess the cryospheric response to early Holocene climate history on
Baffin Island, Arctic Canada, using cosmogenic radionuclide dating of moraines. We present 39 new 10Be
ages from four sets of multi-crested early Holocene moraines deposited by cirque glaciers and ice cap
outlet glaciers, as well as erratic boulders along adjacent fiords to constrain the timing of regional
deglaciation. The age of one moraine is additionally constrained by in situ 14C measurements, which
confirm 10Be inheritance in some samples. All four moraines were deposited between ~9.2 and 8.0 ka,
and their average ages coincide with abrupt coolings at 9.3 and 8.2 ka that are recorded in Greenland ice
cores. Freshwater delivery to the North Atlantic that reduced the flux of warm Atlantic water into Baffin
Bay may explain brief intervals of glacier advance, although moraine formation cannot be definitively
tied to centennial-scale cold reversals. We thus explore other possible contributing factors, including ice
dynamics related to retreat of Laurentide Ice Sheet outlet glaciers. Using a numerical glacier model, we
show that the debuttressing effect of trunk valley deglaciation may have contributed to these morainebuilding
events. These new age constraints and process insights highlight the complex behavior of the
cryosphere during regional deglaciation and suggest that multiple abrupt cold reversalsdas well as
deglacial ice dynamicsdlikely played a role in early Holocene moraine formation on Baffin Island.
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In situ cosmogenic <sup>10</sup>Be–<sup>14</sup>C–<sup>26</sup>Al measurements from recently deglaciated bedrock as a new tool to decipher changes in Greenland Ice Sheet size
Abstract. Sometime during the middle to late Holocene (8.2 ka to ∼ 1850–1900 CE), the Greenland Ice Sheet (GrIS) was smaller than its currentconfiguration. Determining the exact dimensions of the Holocene ice-sheetminimum and the duration that the ice margin rested inboard of its currentposition remains challenging. Contemporary retreat of the GrIS from itshistorical maximum extent in southwestern Greenland is exposing a landscapethat holds clues regarding the configuration and timing of past ice-sheetminima. To quantify the duration of the time the GrIS margin was near itsmodern extent we develop a new technique for Greenland that utilizes in situcosmogenic 10Be–14C–26Al in bedrock samples that have becomeice-free only in the last few decades due to the retreating ice-sheet margin atKangiata Nunaata Sermia (n=12 sites, 36 measurements; KNS), southwest Greenland. To maximizethe utility of this approach, we refine the deglaciation history of the regionwith stand-alone 10Be measurements (n=49) and traditional 14C agesfrom sedimentary deposits contained in proglacial–threshold lakes. We combineour reconstructed ice-margin history in the KNS region with additionalgeologic records from southwestern Greenland and recent model simulations ofGrIS change to constrain the timing of the GrIS minimum in southwestGreenland and the magnitude of Holocene inland GrIS retreat, as well as to explore theregional climate history influencing Holocene ice-sheet behavior. Our10Be–14C–26Al measurements reveal that (1) KNS retreated behindits modern margin just before 10 ka, but it likely stabilized near thepresent GrIS margin for several thousand years before retreating fartherinland, and (2) pre-Holocene 10Be detected in several of our sample sitesis most easily explained by several thousand years of surface exposure duringthe last interglaciation. Moreover, our new results indicate that the minimumextent of the GrIS likely occurred after ∼5 ka, and the GrISmargin may have approached its eventual historical maximum extent as early as∼2 ka. Recent simulations of GrIS change are able to match thegeologic record of ice-sheet change in regions dominated by surface massbalance, but they produce a poorer model–data fit in areas influenced by oceanicand dynamic processes. Simulations that achieve the best model–data fitsuggest that inland retreat of the ice margin driven by early to middleHolocene warmth may have been mitigated by increased precipitation. Triple10Be–14C–26Al measurements in recently deglaciated bedrockprovide a new tool to help decipher the duration of smaller-than-present iceover multiple timescales. Modern retreat of the GrIS margin in southwestGreenland is revealing a bedrock landscape that was also exposed during themigration of the GrIS margin towards its Holocene minimum extent, but it has yetto tap into a landscape that remained ice-covered throughout the entireHolocene.
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- Award ID(s):
- 1755125
- NSF-PAR ID:
- 10317489
- Date Published:
- Journal Name:
- Climate of the Past
- Volume:
- 17
- Issue:
- 1
- ISSN:
- 1814-9332
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/cp-17-419-2021
