An official website of the United States government
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
Age‐Depth Stratigraphy of Pine Island Glacier Inferred From Airborne Radar and Ice‐Core Chronology
Key Points Using airborne radar, we trace four isochronous internal reflecting horizons over Pine Island Glacier, West Antarctica Isochrone ages calculated using the WAIS Divide ice core and a 1‐D model are 2.31–2.92, 4.72 ± 0.28, 6.94 ± 0.31, and 16.50 ± 0.79 ka We show that these isochrones are widespread across Pine Island Glacier and extend into neighboring Weddell and Amundsen Sea regions
more »
« less
- Award ID(s):
- 1043761
- PAR ID:
- 10450545
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 126
- Issue:
- 4
- ISSN:
- 2169-9003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
ABSTRACT The catchments of Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are two of the largest, most rapidly changing, and potentially unstable sectors of the West Antarctic Ice Sheet. They are also neighboring outlets, separated by the topographically unconfined eastern shear margin of Thwaites Glacier and the southwest tributary of Pine Island Glacier. This tributary begins just downstream of the eastern shear margin and flows into the Pine Island ice shelf. As a result, it is a potential locus of interaction between the two glaciers and could result in cross-catchment feedback during the retreat of either. Here, we analyze relative basal reflectivity profiles from three radar sounding survey lines collected using the UTIG HiCARS radar system in 2004 and CReSIS MCoRDS radar system in 2012 and 2014 to investigate the extent and character of ocean access beneath the southwest tributary. These profiles provide evidence of ocean access ~12 km inland of the 1992–2011 InSAR-derived grounding line by 2014, suggesting either retreat since 2011 or the intrusion of ocean water kilometers inland of the grounding line.more » « less
-
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 ɛHfisotope 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.more » « less
-
Abstract We have located 117 previously undetected seismic events mainly occurring between 2015 and 2017 that originated from glacial, tectonic, and volcanic processes in central West Antarctica using data recorded on Polar Earth Observing Network (POLENET/ANET) and UK Antarctic Network (UKANET) seismic stations. The seismic events, with local magnitudes (ML) ranging from 1.1 to 3.5, are predominantly clustered in four geographic regions; the Ellsworth Mountains, Thwaites Glacier, Pine Island Glacier, and Mount Takahe. Eighteen of the events are in the Ellsworth Mountains and can be attributed to a mixture of glacial and tectonic processes. The largest event noted in this study was a mid‐crustal (∼19 km focal depth;ML3.5) normal mechanism earthquake beneath Thwaites Glacier. We also located 91 glacial events near the grounding zones of Thwaites Glacier and Pine Island Glacier that are predominantly associated with time periods of significant calving activity. Eight events, likely arising from volcano‐tectonic processes, occurred beneath Mount Takahe. Using Pn travel times from the seismic events, we find laterally variable uppermost mantle structure in central West Antarctica. On average, the Ellsworth Mountains are underlain by a faster mantle lid (VPn = ∼8.4 km/s) compared to the Amundsen Sea Embayment region (VPn = ∼8.1 km/s). Within the Amundsen Sea Embayment itself, we find mantle lid velocities ranging from ∼8.05 to 8.18 km/s. Laterally heterogeneous uppermost mantle structure, indicative of variable thermal and rheological structure, likely influences both geothermal heat flux and glacial isostatic adjustment spatial patterns and rates within central West Antarctica.more » « less
-
Abstract The Amundsen Sea Embayment of the West Antarctic Ice Sheet contains Thwaites and Pine Island Glaciers, two of the most rapidly changing glaciers in Antarctica. To date, Pine Island and Thwaites Glaciers have only been observed by independent airborne radar sounding surveys, but a combined cross‐basin analysis that investigates the basal conditions across the Pine Island‐Thwaites Glaciers boundary has not been performed. Here, we combine two radar surveys and correct for their differences in system parameters to produce unified englacial attenuation and basal relative reflectivity maps spanning both Pine Island and Thwaites Glaciers. Relative reflectivities range from −24.8 to +37.4 dB with the highest values beneath fast‐flowing ice at the ice sheet margin. By comparing our reflectivity results with previously derived radar specularity and trailing bed echoes at Thwaites Glacier, we find a highly diverse subglacial landscape and hydrologic conditions that evolve along‐flow. Together, these findings highlight the potential for joint airborne radar analysis with ground‐based seismic and geomorphological observations to understand variations in the bed properties and cross‐catchment interactions of ice streams and outlet glaciers.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1029/2020JF005927
