Siegfried
Matthew R.
Siegfried
Matthew R.
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ArticleScientific access into Mercer Subglacial Lake: scientific objectives, drilling operations and initial observations(Cambridge University Press, 2021-01-08) Priscu, John C. ; Kalin, Jonas ; Winans, John ; Campbell, Timothy ; Siegfried, Matthew R. ; Skidmore, Mark ; Dore, John E. ; Leventer, Amy ; Harwood, David M. ; Duling, Dennis ; Zook, Robert ; Burnett, Justin ; Gibson, Dar ; Krula, Edward ; Mironov, Anatoly ; McManis, James ; Roberts, Graham ; Rosenheim, Brad E. ; Christner, Brent C. ; Kasic, Kathy ; Fricker, Helen A. ; Lyons, W. Berry ; Barker, Joel ; Bowling, Mark ; Collins, Billy ; Davis, Christina ; Gagnon, Alan R. ; Gardner, Christopher B. ; Gustafson, Chloe ; Kim, Ok-Sun ; Li, Wei ; Michaud, Alex ; Patterson, Molly O. ; Tranter, Martyn ; Venturelli, Ryan ; Vick-Majors, Trista ; Elsworth, CooperThe Subglacial Antarctic Lakes Scientific Access (SALSA) Project accessed Mercer Subglacial Lake using environmentally clean hot-water drilling to examine interactions among ice, water, sediment, rock, microbes and carbon reservoirs within the lake water column and underlying sediments. A ~0.4 m diameter borehole was melted through 1087 m of ice and maintained over ~10 days, allowing observation of ice properties and collection of water and sediment with various tools. Over this period, SALSA collected: 60 L of lake water and 10 L of deep borehole water; microbes >0.2 μm in diameter from in situ filtration of ~100 L of lake water; 10 multicores 0.32–0.49 m long; 1.0 and 1.76 m long gravity cores; three conductivity–temperature–depth profiles of borehole and lake water; five discrete depth current meter measurements in the lake and images of ice, the lake water–ice interface and lake sediments. Temperature and conductivity data showed the hydrodynamic character of water mixing between the borehole and lake after entry. Models simulating melting of the ~6 m thick basal accreted ice layer imply that debris fall-out through the ~15 m water column to the lake sediments from borehole melting had little effect on the stratigraphy of surficial sediment cores.
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ArticleConstraints on the timing and extent of deglacial grounding line retreat in West Antarctica(American Geophysical Union, 2023-04-26) Venturelli, Ryan A. ; Boehman, Brenna ; Davis, Christina ; Hawkings, Jon R. ; Johnston, Sarah E. ; Gustafson, Chloe D. ; Michaud, Alexander B. ; Mosbeux, Cyrille ; Siegfried, Matthew R. ; Vick‐Majors, Trista J. ; Galy, Valier ; Spencer, Robert G. M. ; Warny, Sophie ; Christner, Brent C. ; Fricker, Helen A. ; Harwood, David M. ; Leventer, Amy ; Priscu, John C. ; Rosenheim, Brad E.Projections of Antarctica's contribution to future sea level rise are associated with significant uncertainty, in part because the observational record is too short to capture long‐term processes necessary to estimate ice mass changes over societally relevant timescales. Records of grounding line retreat from the geologic past offer an opportunity to extend our observations of these processes beyond the modern record and to gain a more comprehensive understanding of ice‐sheet change. Here, we present constraints on the timing and inland extent of deglacial grounding line retreat in the southern Ross Sea, Antarctica, obtained via direct sampling of a subglacial lake located 150 km inland from the modern grounding line and beneath >1 km of ice. Isotopic measurements of water and sediment from the lake enabled us to evaluate how the subglacial microbial community accessed radiocarbon‐bearing organic carbon for energy, as well as where it transferred carbon metabolically. Using radiocarbon as a natural tracer, we found that sedimentary organic carbon was microbially translocated to dissolved carbon pools in the subglacial hydrologic system during the 4.5‐year period of water accumulation prior to our sampling. This finding indicates that the grounding line along the Siple Coast of West Antarctica retreated more than 250 km inland during the mid‐Holocene (6.3 ± 1.0 ka), prior to re‐advancing to its modern position.
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ArticleAlongshore winds force warm Atlantic water toward Helheim Glacier in Southeast Greenland(American Geophysical Union, 2023-09-07) Snow, Tasha ; Zhang, Weifeng Gordon ; Schreiber, Erika A. P. ; Siegried, Matthew R. ; Abdalati, Waleed ; Scambos, Ted A.Enhanced transport of warm subsurface Atlantic Water (AW) into Greenland fjords has driven glacier mass loss, but the mechanisms transporting AW to the fjords remain poorly characterized. Here, we provide the first direct satellite-based observations of rapid (∼0.2 m/s) AW intrusion toward Sermilik Fjord abutting Helheim Glacier, one of Greenland's largest glaciers. The intrusions arise when coastal upwelling—through interactions with Sermilik's bathymetric trough on the continental shelf—triggers enhanced AW upwelling and inflow that can travel tens of kilometers along the trough within hours. A weakening or reversal of northeasterly alongshore winds stimulates the intrusions and is often associated with the passing of cyclones and subsequent sea surface lowering. Mooring data show that these intrusions produce subsurface ocean warming both at Sermilik Fjord mouth and within the fjord and that the warming signal in the fjord does not diminish during subsequent coastal downwelling events. Satellite imagery captures near-synchronous AW intrusions at multiple troughs rimming southeast Greenland suggesting that these wind-driven processes may play a substantial role in ocean heat transport toward the Greenland Ice Sheet.