TY - JOUR
T1 - Deglaciation of Pope Glacier implies widespread early Holocene ice sheet thinning in the Amundsen Sea sector of Antarctica
AU - Johnson, Joanne S.
AU - Roberts, Stephen J.
AU - Rood, Dylan H.
AU - Pollard, David
AU - Schaefer, Joerg M.
AU - Whitehouse, Pippa L.
AU - Ireland, Louise C.
AU - Lamp, Jennifer L.
AU - Goehring, Brent M.
AU - Rand, Cari
AU - Smith, James A.
N1 - Funding Information:
We are grateful to British Antarctic Survey (BAS) Operations and Air Unit, and all staff at Rothera Research Station who made the fieldwork possible, especially field guides Alistair Docherty and Iain Rudkin whose professionalism and skill in the field were exemplary. John Smellie and Wes LeMasurier kindly provided information on sampling sites around Mt Murphy from their earlier field observations, and Hilary Blagbrough and Laura Gerrish (BAS), Jean Hanley (LDEO), Roseanne Schwartz (LDEO) and Sheng Xu (SUERC) provided technical support. Richard Selwyn Jones (Durham University) advised on data analysis for Fig. 7 . The work has benefited from numerous conversations and collaborations with colleagues over the past decade, especially Claus-Dieter Hillenbrand, Richard Hindmarsh, Rob Larter and David Vaughan at BAS, John Smellie (University of Leicester), and Mike Bentley (Durham University). Some of the samples from Kay Peak ridge were collected in 2010 (see Table 1 ) whilst James Smith was on board RV Polarstern cruise ANT-XXVII-3. We acknowledge the support of Natural Environment Research Council (NERC) grants NE/K012088/1 , NE/K011278/1 and NE/M013081/1 . This work forms part of the British Antarctic Survey ‘Polar Science for Planet Earth’ programme, also funded by NERC . We are grateful for constructive comments from two anonymous reviewers that helped improve the manuscript.
Funding Information:
We are grateful to British Antarctic Survey (BAS) Operations and Air Unit, and all staff at Rothera Research Station who made the fieldwork possible, especially field guides Alistair Docherty and Iain Rudkin whose professionalism and skill in the field were exemplary. John Smellie and Wes LeMasurier kindly provided information on sampling sites around Mt Murphy from their earlier field observations, and Hilary Blagbrough and Laura Gerrish (BAS), Jean Hanley (LDEO), Roseanne Schwartz (LDEO) and Sheng Xu (SUERC) provided technical support. Richard Selwyn Jones (Durham University) advised on data analysis for Fig. 7. The work has benefited from numerous conversations and collaborations with colleagues over the past decade, especially Claus-Dieter Hillenbrand, Richard Hindmarsh, Rob Larter and David Vaughan at BAS, John Smellie (University of Leicester), and Mike Bentley (Durham University). Some of the samples from Kay Peak ridge were collected in 2010 (see Table 1) whilst James Smith was on board RV Polarstern cruise ANT-XXVII-3. We acknowledge the support of Natural Environment Research Council (NERC) grants NE/K012088/1, NE/K011278/1 and NE/M013081/1. This work forms part of the British Antarctic Survey ?Polar Science for Planet Earth? programme, also funded by NERC. We are grateful for constructive comments from two anonymous reviewers that helped improve the manuscript.
Publisher Copyright:
© 2020 The Author(s)
PY - 2020/10/15
Y1 - 2020/10/15
N2 - The Amundsen Sea sector of the Antarctic ice sheet presently dominates the contribution from Antarctica to sea level rise. Several large ice streams that currently drain the sector have experienced rapid flow acceleration, grounding line retreat and thinning during the past few decades. However, little is known of their longer-term – millennial-scale – retreat history, despite the reliance of several ice sheet and glacial-isostatic adjustment models on such data for improving sea level prediction from this critical region. This study investigates the timing and extent of surface lowering of one of those ice streams, Pope Glacier, since the Last Glacial Maximum (LGM), using glacial-geological evidence for former ice cover. We present a new deglacial chronology for the glacier, derived from surface exposure dating of glacially-deposited cobbles and ice-scoured bedrock from Mount Murphy and its surrounding peaks. Cosmogenic 10Be exposure ages from 44 erratic cobbles and 5 bedrock samples, and in situ 14C exposure ages from one erratic and 8 bedrock samples are predominantly in the range 5.5-16 ka. Although 10Be inheritance from prior exposure is prevalent in some erratics and probably all bedrock samples, none of the ages pre-date the LGM. From these results we infer that the surface of Pope Glacier lowered by 560 m during the early- to mid-Holocene (9-6 ka), at an average rate of 0.13 ± 0.09/0.04 m yr−1. The lowering coincided with a period of enhanced upwelling of warm Circumpolar Deep Water onto the continental shelf in the region. A reduction in buttressing − facilitated by such upwelling − by an ice shelf that is thought to have spanned the embayment until 10.6 cal kyr BP could have triggered simultaneous early Holocene thinning of Pope Glacier and glaciers elsewhere in the Amundsen Sea Embayment.
AB - The Amundsen Sea sector of the Antarctic ice sheet presently dominates the contribution from Antarctica to sea level rise. Several large ice streams that currently drain the sector have experienced rapid flow acceleration, grounding line retreat and thinning during the past few decades. However, little is known of their longer-term – millennial-scale – retreat history, despite the reliance of several ice sheet and glacial-isostatic adjustment models on such data for improving sea level prediction from this critical region. This study investigates the timing and extent of surface lowering of one of those ice streams, Pope Glacier, since the Last Glacial Maximum (LGM), using glacial-geological evidence for former ice cover. We present a new deglacial chronology for the glacier, derived from surface exposure dating of glacially-deposited cobbles and ice-scoured bedrock from Mount Murphy and its surrounding peaks. Cosmogenic 10Be exposure ages from 44 erratic cobbles and 5 bedrock samples, and in situ 14C exposure ages from one erratic and 8 bedrock samples are predominantly in the range 5.5-16 ka. Although 10Be inheritance from prior exposure is prevalent in some erratics and probably all bedrock samples, none of the ages pre-date the LGM. From these results we infer that the surface of Pope Glacier lowered by 560 m during the early- to mid-Holocene (9-6 ka), at an average rate of 0.13 ± 0.09/0.04 m yr−1. The lowering coincided with a period of enhanced upwelling of warm Circumpolar Deep Water onto the continental shelf in the region. A reduction in buttressing − facilitated by such upwelling − by an ice shelf that is thought to have spanned the embayment until 10.6 cal kyr BP could have triggered simultaneous early Holocene thinning of Pope Glacier and glaciers elsewhere in the Amundsen Sea Embayment.
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U2 - 10.1016/j.epsl.2020.116501
DO - 10.1016/j.epsl.2020.116501
M3 - Article
AN - SCOPUS:85089214754
VL - 548
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
SN - 0012-821X
M1 - 116501
ER -