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Research Interests: Geology and Ice stream
Research Interests: Glacier and Ice stream
High-resolution seismic data collected aboard the R/V Maurice Ewing in August-September, 2004 imaged glacial fjords throughout southeast Alaska and the glacially- dominated shelf offshore the largest temperate glaciers in the world.... more
High-resolution seismic data collected aboard the R/V Maurice Ewing in August-September, 2004 imaged glacial fjords throughout southeast Alaska and the glacially- dominated shelf offshore the largest temperate glaciers in the world. Individual fjords show from 2-10 glacial advance-retreat sequences, whereas the high-resolution and deeper penetrating seismic data show the continental shelf records glacial advance and retreat sequences back to the
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Research Interests: Geology and Paleontology
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Two high-resolution seismic-reflection profiles collected 13 years apart along the axis of Muir Inlet show the growth of a grounding-line fan to an ice-contact delta at the terminus of Muir Glacier (Fig. 1). During this time, the position... more
Two high-resolution seismic-reflection profiles collected 13 years apart along the axis of Muir Inlet show the growth of a grounding-line fan to an ice-contact delta at the terminus of Muir Glacier (Fig. 1). During this time, the position of the terminus was quasi-stable and the submarine fan grew to sea level, changing the glacier terminus from tidewater to terrestrial [cf Powell, 1990].
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Stratigraphic drilling from the McMurdo Ice Shelf in the 2006/2007 austral summer recovered a 1284.87 m sedimentary succession from beneath the sea floor. Key age data for the core include magnetic polarity stratigraphy for the entire... more
Stratigraphic drilling from the McMurdo Ice Shelf in the 2006/2007 austral summer recovered a 1284.87 m sedimentary succession from beneath the sea floor. Key age data for the core include magnetic polarity stratigraphy for the entire succession, diatom biostratigraphy for the upper 600m and 40Ar/39Ar ages for in-situ volcanic deposits as well as reworked volcanic clasts. A vertical seismic profile for the drill hole allows correlation between the drill hole and a regional seismic network and inference of age constraint by correlation with ...
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The Early to mid-Pliocene (4.5-3.2 Ma) was a prolonged period of global warmth, with average surface temperatures ~3-4°C above present and atmospheric CO2 concentrations of ~400 ppmv. Subsequent cooling culminated in continental-scale... more
The Early to mid-Pliocene (4.5-3.2 Ma) was a prolonged period of global warmth, with average surface temperatures ~3-4°C above present and atmospheric CO2 concentrations of ~400 ppmv. Subsequent cooling culminated in continental-scale Northern Hemisphere glaciation by ~2.7 Ma, and has been attributed to a combination of declining pCO2, changing orbital geometries, closure of the Panamanian Seaway, and enhanced poleward oceanic
Research Interests: Geology, Climate Change, Time Series, Heat Transport, Stratification, and 14 moreSea Ice, Southern Ocean, Stable Isotope, Ocean Circulation, Land Surface Temperature, Oxygen Isotope, Southern Hemisphere, Northern Hemisphere, Temperature Gradient, West Antarctic Ice Sheet, Ice Sheets, Ross Sea, Global Cooling, and surface temperature
The marine sedimentary deposits that accumulated within the basins of Muir Inlet, a deep (150-300 m), narrow (<2.5 km), 48 km-long silled-fjord have been interpreted based on known history of glacial advance and retreat. Ten basins... more
The marine sedimentary deposits that accumulated within the basins of Muir Inlet, a deep (150-300 m), narrow (<2.5 km), 48 km-long silled-fjord have been interpreted based on known history of glacial advance and retreat. Ten basins were imaged by two sets of high-...
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We are investigating sediments from the fjords and continental margin of southern Alaska to develop high-resolution climatic and oceanographic records for the Late Quaternary. Our goal is to better understand linkages between climatic,... more
We are investigating sediments from the fjords and continental margin of southern Alaska to develop high-resolution climatic and oceanographic records for the Late Quaternary. Our goal is to better understand linkages between climatic, terrestrial and oceanic systems in this tectonically active and biologically productive region. A field program was conducted aboard the R/V Maurice Ewing in August/September 2004 utilizing geophysical surveys (high-resolution swath bathymetric and backscatter imaging, shallow ...
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The WISSARD project is a large, NSF-funded, interdisciplinary initiative focused on scientific drilling, exploration, and investigation of Antarctic subglacial aquatic environments. The project consists of three interrelated components:... more
The WISSARD project is a large, NSF-funded, interdisciplinary initiative focused on scientific drilling, exploration, and investigation of Antarctic subglacial aquatic environments. The project consists of three interrelated components: (1) LISSARD - Lake and Ice Stream Subglacial Access Research Drilling, (2) RAGES - Robotic Access to Grounding-zones for Exploration and Science, and (3) GBASE - GeomicroBiology of Antarctic Subglacial Environments). A
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Liquid water occurs below glaciers and ice sheets globally, enabling the existence of an array of aquatic microbial ecosystems. In Antarctica, large subglacial lakes are present beneath hundreds to thousands of metres of ice, and... more
Liquid water occurs below glaciers and ice sheets globally, enabling the existence of an array of aquatic microbial ecosystems. In Antarctica, large subglacial lakes are present beneath hundreds to thousands of metres of ice, and scientific interest in exploring these environments has escalated over the past decade. After years of planning, the first team of scientists and engineers cleanly accessed and retrieved pristine samples from a West Antarctic subglacial lake ecosystem in January 2013. This paper reviews the findings to date on Subglacial Lake Whillans and presents new supporting data on the carbon and energy metabolism of resident microbes. The analysis of water and sediments from the lake revealed a diverse microbial community composed of bacteria and archaea that are close relatives of species known to use reduced N, S or Fe and CH4 as energy sources. The water chemistry of Subglacial Lake Whillans was dominated by weathering products from silicate minerals with a minor i...
Research Interests: Environmental Science, Oceanography, Biogeochemistry, Geomicrobiology, Microbial diversity, and 15 moreMedicine, Multidisciplinary, Lakes, Aquatic Ecosystem, Antarctica, Archaea, Bacteria, Subglacial lakes, Glacier, Ecosystem, Aquatic organisms, Microbial Diversity, Earth Science, Geologic Sediments, and Biogeochemical Cycle
(Table S1) Diatom abundance according to ice cycles in ANDRILL AND1-1B drill core, supplement to: McKay, Robert M; Naish, Tim R; Carter, Lionel; Riesselman, Christina R; Dunbar, Robert G; Winter, Diane M; Sjunneskog, Charlotte; Sangiorgi, Francesca; Warren, Courtney E; Pagani, Mark; Schouten, Ste...more
The influence of Antarctica and the Southern Ocean on Late Pliocene global climate reconstructions has remained ambiguous due to a lack of well-dated Antarctic-proximal, paleoenvironmental records. Here we present ice sheet, sea-surface... more
The influence of Antarctica and the Southern Ocean on Late Pliocene global climate reconstructions has remained ambiguous due to a lack of well-dated Antarctic-proximal, paleoenvironmental records. Here we present ice sheet, sea-surface temperature, and sea ice reconstructions from the ANDRILL AND-1B sediment core recovered from beneath the Ross Ice Shelf. We provide evidence for a major expansion of an ice sheet in the Ross Sea that began at ~3.3 Ma, followed by a coastal sea surface temperature cooling of ~2.5°C, a stepwise expansion of sea ice, and polynya-style deep mixing in the Ross Sea between 3.3 and 2.5 Ma. The intensification of Antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation. The associated northward migration of Southern Ocean fronts has been linked with reduced Atlantic Meridional Overturning Circulation by restricting surface water connectivity between the ocean basins, with implications for heat transport to the high latitud...
Environmental analysis on sediment core CRP-2 from the Ross Sea, Antarctica, supplement to: Powell, Ross; Krissek, Lawrence A; van der Meer, Jaap (2000): Preliminary depositional environmental analysis of CRP-2/2A, Victoria Land Basin, Antarctica: palaeoglaciological and palaeoclimatic inferences...more
Cape Roberts Project drill core 2/2A was obtained from Roberts Ridge, a sea-floor high located at 77° S, 16 km offshore from Cape Roberts in western McMurdo Sound, Antarctica. The recovered core is about 624 m long and includes strata... more
Cape Roberts Project drill core 2/2A was obtained from Roberts Ridge, a sea-floor high located at 77° S, 16 km offshore from Cape Roberts in western McMurdo Sound, Antarctica. The recovered core is about 624 m long and includes strata dated as being Quaternary, Pliocene, Miocene and Oligocene in age. The core includes twelve facies commonly occurring in associations that are repeated in particular sequences throughout the core and which are interpreted as representing different depositional environments through time. Depositional systems inferred to be represented in the succession include: outer shelf with minor iceberg influence, outer shelf-inner shelf-nearshore to shoreface under iceberg influence, deltaic and/or grounding-line fan, and ice proximal-ice marginal-subglacial (mass flow/rainout diamictite/subglacial till) singly or in combination. Changes in palaeoenvironmental interpretations up the core are used to estimate relative glacial proximity to the site through time. The...
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Core scans and lithologic analysis of Subglacial Lake Whillans sediment cores, supplement to: Hodson, Timothy O; Powell, Ross; Brachfield, Stefanie; Tulaczyk, Slawek; Scherer, Reed P; WISSARD Science Team (2016): Physical processes in Subglacial Lake Whillans, West Antarctica: inferences from sed...more
The hydrologic system beneath the Antarctic Ice Sheet is thought to influence both the dynamics and distribution of fast flowing ice streams, which discharge most of the ice lost by the ice sheet. Despite considerable interest in... more
The hydrologic system beneath the Antarctic Ice Sheet is thought to influence both the dynamics and distribution of fast flowing ice streams, which discharge most of the ice lost by the ice sheet. Despite considerable interest in understanding this subglacial network and its affect on ice flow, in situ observations from the ice sheet bed are exceedingly rare. Here we describe the first sediment cores recovered from an active subglacial lake. The lake, known as Subglacial Lake Whillans, is part of a broader, dynamic hydrologic network beneath the Whillans Ice Stream in West Antarctica. Even though "floods" pass through the lake, the lake floor shows no evidence of erosion or deposition by flowing water. By inference, these floods must have insufficient energy to erode or transport significant volumes of sediment coarser than silt. Consequently, water flow beneath the region is probably incapable of incising continuous channels into the bed and instead follows preexisting su...
Amplicon sequencing dataset (Illumina MiSeq) of Bacteria and Archaea (16S) in the marine cavity beneath the McMurdo Ice Shelf, Antarctica
Cape Roberts Project drill core 3 (CRP-3) was obtained from Roberts ridge, a sea-floor high located at 77°S, 12 km offshore from Cape Roberts in western McMurdo Sound, Antarctica. The recovered core is about 939 m long and comprises... more
Cape Roberts Project drill core 3 (CRP-3) was obtained from Roberts ridge, a sea-floor high located at 77°S, 12 km offshore from Cape Roberts in western McMurdo Sound, Antarctica. The recovered core is about 939 m long and comprises strata dated as being early Oligocene (possibly latest Eocene) in age, resting unconformably on ~116 m of basement rocks consisting of Palaeozoic Beacon Supergroup sediments. The core includes ten facies commonly occurring in five major associations that are repeated in particular sequences throughout the core and which are interpreted as representing different depositional environments through time. Depositional systems inferred to be represented in the succession include: outer shelf, inner shelf, nearshore to shoreface each under iceberg influence, deltaic and/or grounding-line fan, and ice proximal-ice marginal-subglacial (mass flow/rainout diamictite/subglacial till) singly or in combination. The record is taken to represent the initial talus/alluvial fan setting of a glaciated rift margin adjacent to the block-uplifted Transantarctic Mountains. Development of a deltaic succession upcore was probably associated with the formation of palaeo-Mackay valley with temperate glaciers in its headwaters. At that stage glaciation was intense enough to support glaciers ending in the sea elsewhere along the coast, but a local glacier was fluctuating down to the sea by the time the youngest part of CRP-3 was being deposited. Changes in palaeoenvironmental interpretations in this youngest part of the core are used to estimate relative glacial proximity to the drillsite through time. These inferred glacial fluctuations are compared with the global d180 and Mg/Ca curves to evaluate the potential of glacial fluctuations on Antarctica for influencing these records of global change. Although the comparisons are tentative at present, the records do have similarities, but there are also some differences that require further evaluation.
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In the 2006/2007 Austral summer, the ANDRILL project recovered a 1,285 m Neogene drillcore (AND-1B) from the Victoria Land Basin beneath the McMurdo Ice Shelf (78 S), SW Ross Sea, Antarctica. Chronostratigraphic data available for the... more
In the 2006/2007 Austral summer, the ANDRILL project recovered a 1,285 m Neogene drillcore (AND-1B) from the Victoria Land Basin beneath the McMurdo Ice Shelf (78 S), SW Ross Sea, Antarctica. Chronostratigraphic data available for the upper 700 m of the drillcore include diatom biostratigraphy, magnetostratigraphy, 40Ar/39Ar ages, 87Sr/86Sr ages and surfaces of erosion identified from physical appearance in the drillcore. The age data allow a relatively well-constrained age model to be constructed and allow ...
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Since 2003, the PIs have been administering an REU site in the Svalbard archipelago for motivated geoscience undergraduate students, directly involving them in important climate change research and exposing them to the challenges and... more
Since 2003, the PIs have been administering an REU site in the Svalbard archipelago for motivated geoscience undergraduate students, directly involving them in important climate change research and exposing them to the challenges and rewards of conducting high latitude research. Funds are provided to continue the Svalbard REU program for another year, based on the success of the program. Student research focuses on the climatic and surficial processes that operate in rapidly changing glacial, lacustrine, and fjord systems that may, in turn, archive the signature of anthropogenic changes in the high Arctic. Students define their research questions and design specific testable hypotheses throughout the program, complete their research projects at their home institutions during the following academic year and present their results at a professional conference. Most alumni of the program have gone into graduate programs better prepared for fundamental research.
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The upper 1200 m of pre-Pliocene sediment recovered by Cape Roberts Project (CRP) drilling off the Victoria Land coast of Antarctica between 1997-1999 has been subdivided into 54 unconformity-bound stratigraphic sequences, spanning the... more
The upper 1200 m of pre-Pliocene sediment recovered by Cape Roberts Project (CRP) drilling off the Victoria Land coast of Antarctica between 1997-1999 has been subdivided into 54 unconformity-bound stratigraphic sequences, spanning the period c. 32 to 17 Ma. The sequences are recognised on the basis of the cyclical vertical stacking of their constituent lithofacies, which are enclosed by erosion surfaces produced during the grounding of the advancing ice margin onto the sea floor. Each sequence represents deposition in a range of offshore shelf to coastal glacimarine sedimentary environments during oscillations in the ice margin across the Western Ross Sea shelf, and coeval fluctuations in water depth. This paper applies spectral analysis techniques to depth- and time-series of sediment grain size (500 samples) for intervals of the core with adequate chronological data. Time series analysis of 0.5-l.0m-spaced grainsize data spanning sequences 9-11 (CRP-2/2A) and sequences 1-7 (CRP-3) suggests that the length of individual sequences correspond to Milankovitch frequencies, probably 41 k.y., but possibly as low as 100 k.y. Higher frequency periodic components at 23 k.y. (orbital precession) and 15-10 k.y. (sub-orbital) are recognised at the intrasequence-scale, and may represent climatic cycles akin to the ice rafting episodes described in the North Atlantic Ocean during the Quaternary. The cyclicity recorded by glacimarine sequences in CRP core provides direct evidence from the periphery of Antarctica for orbital oscillations in the size of the Oligocene-Early Miocene East Antarctic Ice Sheet.
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Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages (Hays et al., 1976,... more
Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages (Hays et al., 1976, doi:10.1126/science.194.4270.1121), fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles (Raymo and Huybers, 2008, doi:10.1038/nature06589). Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch (~5-3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming (Solomon et al., 2007). Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, ~40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to ~3° C warmer than today ( Kim and Crowley, 2000, doi:10.1029/1999PA000459) and atmospheric CO2 concentration was as high as ~400 p.p.m.v. (van der Burgh et al., 1993, doi:10.1126/science.260.5115.1788, Raymo et al., 1996, doi:10.1016/0377-8398(95)00048-8). The evidence is consistent with a new ice-sheet/ice-shelf model (Pollard and DeConto, 2009, doi:10.1038/nature07809) that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and a [...]
Research Interests: Geology and Sediment Core
The site for CRP-3, 12 km east of Cape Roberts (77.006°S; 103.719°E)was selecte to overlap the lower Oligocene strata cored in nearby CRP-2/2A, and to sample the oldest strata in the Victoria Land Basin (VLB) for Paleogene climatic and... more
The site for CRP-3, 12 km east of Cape Roberts (77.006°S; 103.719°E)was selecte to overlap the lower Oligocene strata cored in nearby CRP-2/2A, and to sample the oldest strata in the Victoria Land Basin (VLB) for Paleogene climatic and tectonic history. As it transpired there was ...
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Chronostratigraphic data available for the preliminary age model for the upper 700 m for the AND-1B drill core include diatom biostratigraphy, magnetostratigraphy, 40 Ar/39 Ar ages on volcanic material, 87 Sr/86 Sr ages on calcareous... more
Chronostratigraphic data available for the preliminary age model for the upper 700 m for the AND-1B drill core include diatom biostratigraphy, magnetostratigraphy, 40 Ar/39 Ar ages on volcanic material, 87 Sr/86 Sr ages on calcareous fossil material, and surfaces of erosion identified from physical appearance and facies relationships recognized in the AND-1B drill core. The available age data allow a relatively well-constrained age model to be constructed for the upper 700 m of the drill core. Available diatom biostratigraphic ...