Reversible ice sheet thinning in the Amundsen Sea Embayment during the Late Holocene

Balco, Greg; Brown, Nathan D.; Nichols, Keir; Venturelli, Ryan A.; Adams, Jonathan; Braddock, Scott; Campbell, Seth; Goehring, Brent M.; Johnson, Joanne S.; Rood, Dylan H.; Wilcken, Klaus M.; Hall, Brenda L.; Woodward, John

doi:10.5194/tc-2022-172

Cited by 7 publications

(21 citation statements)

References 32 publications

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“…Samples for cosmogenic nuclide analysis were processed at Tulane University and Imperial College London. All sample pre-treatment, quartz isolation, cosmogenic nuclide extraction and analysis procedures follow those of Balco et al (2023), with the notable exception that froth flotation was not used to isolate any quartz. To summarize, samples were crushed and sieved to extract the 125-710 μm grain size fraction, before the magnetic fraction was removed.…”

Section: Cosmogenic Nuclidesmentioning

confidence: 99%

“…10 Be/ 9 Be isotope ratios were measured at the Centre for Accelerator Science, Australian Nuclear Science and Technology Organisation (ANSTO; Wilcken et al 2022). Beryllium was extracted from quartz in this study at the same time as the samples presented in Balco et al (2023) and Nichols et al (2023). In other words, the two aliquots of quartz processed for 10 Be analysis in this present study were incorporated into two different batches of samples that were processed in the CosmIC Laboratory at Imperial College London, one of which was composed of samples in Balco et al (2023) and the second of samples in Nichols et al (2023).…”

Section: Cosmogenic Nuclidesmentioning

confidence: 99%

“…Beryllium was extracted from quartz in this study at the same time as the samples presented in Balco et al (2023) and Nichols et al (2023). In other words, the two aliquots of quartz processed for 10 Be analysis in this present study were incorporated into two different batches of samples that were processed in the CosmIC Laboratory at Imperial College London, one of which was composed of samples in Balco et al (2023) and the second of samples in Nichols et al (2023). In Balco et al (2023) and Nichols et al (2023), 10 Be concentrations were background corrected using the mean and standard deviation (30 287 ± 8456 atoms) of procedural blanks for the entire series of batches that were processed in succession over a period of a few months.…”

Section: Cosmogenic Nuclidesmentioning

confidence: 99%

“…The in situ 14 C blank correction procedure follows that of Balco et al (2023). In short, we measured 49 procedural blanks during the same measurement period as the in situ 14 C analysis in this present study.…”

Section: Cosmogenic Nuclidesmentioning

confidence: 99%

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Geological insights from the newly discovered granite of Sif Island between Thwaites and Pine Island glaciers

Marschalek,

Thomson,

Hillenbrand

et al. 2024

Antarctic Science

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Large-scale geological structures have controlled the long-term development of the bed and thus the flow of the West Antarctic Ice Sheet (WAIS). However, complete ice cover has obscured the age and exact positions of faults and geological boundaries beneath Thwaites Glacier and Pine Island Glacier, two major WAIS outlets in the Amundsen Sea sector. Here, we characterize the only rock outcrop between these two glaciers, which was exposed by the retreat of slow-flowing coastal ice in the early 2010s to form the new Sif Island. The island comprises granite, zircon U-Pb dated to ~177–174 Ma and characterized by initial ɛNd, 87Sr/86Sr and ɛHf isotope compositions of -2.3, 0.7061 and -1.3, respectively. These characteristics resemble Thurston Island/Antarctic Peninsula crustal block rocks, strongly suggesting that the Sif Island granite belongs to this province and placing the crustal block's boundary with the Marie Byrd Land province under Thwaites Glacier or its eastern shear margin. Low-temperature thermochronological data reveal that the granite underwent rapid cooling following emplacement, rapidly cooled again at ~100–90 Ma and then remained close to the Earth's surface until present. These data help date vertical displacement across the major tectonic structure beneath Pine Island Glacier to the Late Cretaceous.

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Section: Cosmogenic Nuclidesmentioning

confidence: 99%

Section: Cosmogenic Nuclidesmentioning

confidence: 99%

Section: Cosmogenic Nuclidesmentioning

confidence: 99%

Section: Cosmogenic Nuclidesmentioning

confidence: 99%

See 2 more Smart Citations

Geological insights from the newly discovered granite of Sif Island between Thwaites and Pine Island glaciers

Marschalek,

Thomson,

Hillenbrand

et al. 2024

Antarctic Science

View full text Add to dashboard Cite

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“…A more recent example of potential implications of recognizing significant solar modulation of cosmic ray flux is in a study of cosmogenic-nuclide concentrations in subglacial bedrock cores between Thwaites and Pope glaciers in Antarctic where Balco et al (2023) argued that the West Antarctic Ice Sheet (WAIS) at the site was about 35 m thinner several thousand years ago and subsequently thickened to its present thickness. The conclusion basically followed from modeling the concentrations of 10 Be, 26 Al and 14 C measured in cores of the subglacial bedrock that were higher than expected from shielding by present ice thickness, implicitly assuming a uniform present-day cosmic ray flux over the entire Holocene.…”

Section: As Shown Inmentioning

confidence: 99%

Cosmogenic nuclide dating conundrum for retreat of the Laurentide Ice Sheet and the critical roles of geomagnetic and heliomagnetic modulation of cosmic ray flux

Kent¹,

Lanci²,

Peteet³

2023

Preprint

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What we regard as anomalously old 10Be exposure dates reported from the terminal moraine of the Laurentide Ice Sheet (LIS) in northeastern North America, such as recently published for Allamuchy NJ, ostensibly point to the start of deglaciation at 25 thousand calendar years before present (cal. ka). These dates are well within the conventional age span of the Last Glacial Maximum (LGM) and are in stark contrast with published 14C accelerator mass spectrometry (AMS) dates for earliest terrestrial plant macrofossils found in LIS deglacial clay deposits that range back to only ~16 cal. ka, which more plausibly coincide with the known timing of the glacio-eustatic rise and meltwater discharge to the North Atlantic and Gulf of Mexico that mark the demise of the LGM in the marine record. To explore possible explanations for this inconsistency, we first employed a statistical model of the geomagnetic field that includes secular variation with nondipole terms and can be applied globally. The model results in a decrease in the magnetic shielding factor by about 10% at mid-latitudes compared to oft-used geomagnetic scaling schemes. However, the time-integrated axial dipole moment estimated separately suggests little overall change in average shielding since about 20 cal. ka. This seems to leave cosmic ray flux modulated by a time-varying heliomagnetic field linked to sunspot activity as an underestimated factor in widely used 10Be exposure age calculators. If generally biased by about 23% higher compared to modern levels as reported for the past 9.4 cal. ka, the elevated high cosmic ray flux would make 10Be reference production rates proportionately higher, to about 5.5 at/g/y at sea level-high latitude, and reduce exposure ages to about 3/4 of those that have been previously calculated for LGM and younger rocks (to less than 20 cal. ka in the case of Allamuchy). Varying but generally higher solar modulation will require reevaluation of cosmogenic exposure dates in general, as in the case of Allamuchy, that would allow improved synchronization of marine and terrestrial records of glaciation. Other test cases can result in improved GIA deglaciation models and alternative estimates of effects of shielding in ice-flow models.

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Ocean cavity regime shift reversed West Antarctic grounding line retreat in the late Holocene

Lowry,

Han,

Golledge

et al. 2024

Nat Commun

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Recent geologic and modeled evidence suggests that the grounding line of the Siple Coast of the West Antarctic Ice Sheet (WAIS) retreated hundreds of kilometers beyond its present position in the middle to late Holocene and readvanced within the past 1.7 ka. This grounding line reversal has been attributed to both changing rates of isostatic rebound and regional climate change. Here, we test these two hypotheses using a proxy-informed ensemble of ice sheet model simulations with varying ocean thermal forcing, global glacioisostatic adjustment (GIA) model simulations, and coupled ice sheet-GIA simulations that consider the interactions between these processes. Our results indicate that a warm to cold ocean cavity regime shift is the most likely cause of this grounding line reversal, but that GIA influences the rate of ice sheet response to oceanic changes. This implies that the grounding line here is sensitive to future changes in sub-ice shelf ocean circulation.

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Reversible ice sheet thinning in the Amundsen Sea Embayment during the Late Holocene

Cited by 7 publications

References 32 publications

Geological insights from the newly discovered granite of Sif Island between Thwaites and Pine Island glaciers

Geological insights from the newly discovered granite of Sif Island between Thwaites and Pine Island glaciers

Cosmogenic nuclide dating conundrum for retreat of the Laurentide Ice Sheet and the critical roles of geomagnetic and heliomagnetic modulation of cosmic ray flux

Ocean cavity regime shift reversed West Antarctic grounding line retreat in the late Holocene

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