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Abstract Constraining past West Antarctic Ice Sheet (WAIS) change helps validate numerical models simulating future ice sheet dynamics. Following rapid deglaciation during the mid‐Holocene, ice near Thwaites Glacier was ∼35 m thinner than present; however, the timing of ice regrowth to its present configuration remains unknown. To fill this knowledge gap, we present cosmogenic nuclide exposure ages of cobbles from the surface of a moraine situated between Thwaites and Pope glaciers. We infer that the moraine formed and stabilized in the Late Holocene (∼1.4 ka) when a small glacier thickened. We also present a novel reconstruction of WAIS volume constrained by sea‐level data, which demonstrates that moraine formation coincided with a large‐scale WAIS readvance. Our new geologic constraints will help inform models of the solid Earth response to surface mass loading, improving our understanding of ice sheet dynamics in a vulnerable part of WAIS.
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New 10 Be exposure ages improve Holocene ice sheet thinning history near the grounding line of Pope Glacier, Antarctica
Abstract. Evidence for the timing and pace of past grounding lineretreat of the Thwaites Glacier system in the Amundsen Sea embayment (ASE)of Antarctica provides constraints for models that are used to predict thefuture trajectory of the West Antarctic Ice Sheet (WAIS). Existingcosmogenic nuclide surface exposure ages suggest that Pope Glacier, a formertributary of Thwaites Glacier, experienced rapid thinning in the early tomid-Holocene. There are relatively few exposure ages from the lower ice-freesections of Mt. Murphy (<300 m a.s.l.; metres above sea level) that are uncomplicated byeither nuclide inheritance or scatter due to localised topographiccomplexities; this makes the trajectory for the latter stages ofdeglaciation uncertain. This paper presents 12 new 10Be exposure agesfrom erratic cobbles collected from the western flank of Mt. Murphy, within160 m of the modern ice surface and 1 km from the present grounding line.The ages comprise two tightly clustered populations with mean deglaciationages of 7.1 ± 0.1 and 6.4 ± 0.1 ka (1 SE). Linear regressionanalysis applied to the age–elevation array of all available exposure agesfrom Mt. Murphy indicates that the median rate of thinning of Pope Glacierwas 0.27 m yr−1 between 8.1–6.3 ka, occurring 1.5 times faster thanpreviously thought. Furthermore, this analysis better constrains theuncertainty (95 % confidence interval) in the timing of deglaciation atthe base of the Mt. Murphy vertical profile (∼ 80 m above themodern ice surface), shifting it to earlier in the Holocene (from 5.2 ± 0.7 to 6.3 ± 0.4 ka). Taken together, the results presentedhere suggest that early- to mid-Holocene thinning of Pope Glacier occurredover a shorter interval than previously assumed and permit a longer durationover which subsequent late Holocene re-thickening could have occurred.
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- Award ID(s):
- 2317097
- PAR ID:
- 10403976
- Date Published:
- Journal Name:
- The Cryosphere
- Volume:
- 16
- Issue:
- 12
- ISSN:
- 1994-0424
- Page Range / eLocation ID:
- 4887 to 4905
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract. Cosmogenic-nuclide concentrations in subglacial bedrock cores show that the West Antarctic Ice Sheet (WAIS) at a site between Thwaites and Pope glaciers was at least 35 m thinner than present in the past several thousand years and then subsequently thickened. This is important because of concern that present thinning and grounding line retreat at these and nearby glaciers in the Amundsen Sea Embayment may irreversibly lead to deglaciation of significant portions of the WAIS, with decimeter- to meter-scale sea level rise within decades to centuries. A past episode of ice sheet thinning that took place in a similar, although not identical, climate was not irreversible. We propose that the past thinning–thickening cycle was due to a glacioisostatic rebound feedback, similar to that invoked as a possible stabilizing mechanism for current grounding line retreat, in which isostatic uplift caused by Early Holocene thinning led to relative sea level fall favoring grounding line advance.more » « less
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Abstract Pine Island Glacier, West Antarctica, is the largest Antarctic contributor to global sea-level rise and is vulnerable to rapid retreat, yet our knowledge of its deglacial history since the Last Glacial Maximum is based largely on marine sediments that record a retreat history ending in the early Holocene. Using a suite of 10Be exposure ages from onshore glacial deposits directly adjacent to Pine Island Glacier, we show that this major glacier thinned rapidly in the early to mid-Holocene. Our results indicate that Pine Island Glacier was at least 690 m thicker than present prior to ca. 8 ka. We infer that the rapid thinning detected at the site farthest downstream records the arrival and stabilization of the retreating grounding line at that site by 8–6 ka. By combining our exposure ages and the marine record, we extend knowledge of Pine Island Glacier retreat both spatially and temporally: to 50 km from the modern grounding line and to the mid-Holocene, providing a data set that is important for future numerical ice-sheet model validation.more » « less
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Cosmogenic-nuclide concentrations in subglacial bedrock cores show that theWest Antarctic Ice Sheet (WAIS) at a site between Thwaites and Pope glaciers was at least 35m thinner than present in the past several thousand years and then subsequently thickened. This is important because of concern that present thinning and grounding line retreat at these and nearby glaciers in the Amundsen Sea Embayment may irreversibly lead to deglaciation of significant portions of the WAIS, with decimeter- to meter-scale sea level rise within decades to centuries. A past episode of ice sheet thinning that took place in a similar, although not identical, climate was not irreversible.We propose that the past thinning– thickening cycle was due to a glacioisostatic rebound feedback, similar to that invoked as a possible stabilizing mechanism for current grounding line retreat, in which isostatic uplift caused by Early Holocene thinning led to relative sea level fall favoring grounding line advance.more » « less
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Abstract. Chronologies of glacier deposits in the Transantarctic Mountains provide important constraints on grounding-line retreat during the last deglaciation in the Ross Sea. However, between Beardmore Glacier and Ross Island – a distance of some 600 km – the existing chronologies are generally sparse and far from the modern grounding line, leaving the past dynamics of this vast region largely unconstrained. We present exposure ages of glacial deposits at three locations alongside the Darwin–Hatherton Glacier System – including within 10 km of the modern grounding line – that record several hundred meters of Late Pleistocene to Early Holocene thickening relative to present. As the ice sheet grounding line in the Ross Sea retreated, Hatherton Glacier thinned steadily from about 9 until about 3 ka. Our data are equivocal about the maximum thickness and Mid-Holocene to Early Holocene history at the mouth of Darwin Glacier, allowing for two conflicting deglaciation scenarios: (1) ∼500 m of thinning from 9 to 3 ka, similar to Hatherton Glacier, or (2) ∼950 m of thinning, with a rapid pulse of ∼600 m thinning at around 5 ka. We test these two scenarios using a 1.5-dimensional flowband model, forced by ice thickness changes at the mouth of Darwin Glacier and evaluated by fit to the chronology of deposits at Hatherton Glacier. The constraints from Hatherton Glacier are consistent with the interpretation that the mouth of Darwin Glacier thinned steadily by ∼500 m from 9 to 3 ka. Rapid pulses of thinning at the mouth of Darwin Glacier are ruled out by the data at Hatherton Glacier. This contrasts with some of the available records from the mouths of other outlet glaciers in the Transantarctic Mountains, many of which thinned by hundreds of meters over roughly a 1000-year period in the Early Holocene. The deglaciation histories of Darwin and Hatherton glaciers are best matched by a steady decrease in catchment area through the Holocene, suggesting that Byrd and/or Mulock glaciers may have captured roughly half of the catchment area of Darwin and Hatherton glaciers during the last deglaciation. An ensemble of three-dimensional ice sheet model simulations suggest that Darwin and Hatherton glaciers are strongly buttressed by convergent flow with ice from neighboring Byrd and Mulock glaciers, and by lateral drag past Minna Bluff, which could have led to a pattern of retreat distinct from other glaciers throughout the Transantarctic Mountains.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/tc-16-4887-2022
