A5010143223- Cryospheric studies and observations
- Climate change and permafrost
- Winter Sports Injuries and Performance
- Landslides and related hazards
- Arctic and Antarctic ice dynamics
- Geology and Paleoclimatology Research
- Methane Hydrates and Related Phenomena
- Geophysics and Gravity Measurements
- Atmospheric and Environmental Gas Dynamics
- Planetary Science and Exploration
- Climate variability and models
- GNSS positioning and interference
- Space Exploration and Technology
- Polar Research and Ecology
- Geological Studies and Exploration
- Seismic Waves and Analysis
- Meteorological Phenomena and Simulations
- Hydrocarbon exploration and reservoir analysis
- Astro and Planetary Science
- Soil Moisture and Remote Sensing
- Inertial Sensor and Navigation
- Geophysical Methods and Applications
- Ionosphere and magnetosphere dynamics
- Remote Sensing and LiDAR Applications
- Isotope Analysis in Ecology
Dartmouth College
2016-2025
University of Liverpool
2025
Dartmouth Hospital
2015-2024
University of Nebraska–Lincoln
2018
ETH Zurich
2018
Earth and Space Research
2002-2013
University of Washington
2000-2013
University of Colorado Boulder
1960-2013
University of Cambridge
2006-2009
Scientific Committee on Antarctic Research
2006-2009
Penetration of surface meltwater to the bed Greenland Ice Sheet each summer causes an initial increase in ice speed due elevated basal water pressure, followed by slowdown late that continues into fall and winter. While this seasonal pattern is commonly explained evolution subglacial drainage system from inefficient distributed efficient channelized configuration, mounting evidence indicates channels are unable explain important aspects hydrodynamic coupling fall. Here we use numerical...
Abstract Ice deformation and basal motion characterize the dynamical behavior of Greenland ice sheet (GrIS). We evaluate contribution from measurements in boreholes drilled to bed at two sites western marginal zone GrIS. find a sustained high amount surface velocity 44–73% winter, up 90% summer. Measured rates show an unexpected variation with depth that can be explained help ice-flow model as consequence stress transfer slippery sticky areas. This effect necessitates use high-order models,...
Abstract Future precipitation changes in a warming climate depend regionally upon the response of natural modes to anthropogenic forcing. North Pacific hydroclimate is dominated by Aleutian Low, semi-permanent wintertime feature characterized frequent low-pressure conditions that influenced tropical Ocean temperatures through Pacific-North American (PNA) teleconnection pattern. Instrumental records show recent increase coastal Alaskan and Low intensification, but are insufficient length...
Abstract Current understanding of ice dynamics predicts that increasing availability and variability meltwater will have an impact on basal motion therefore the evolution future behavior Greenland sheet. We present measurements deformation, subglacial water pressure, surface velocity show periodic episodic variations several time scales (seasonal, multiday, diurnal). These variations, observed with GPS sensors at different depths throughout column, are not synchronous but delayed responses...
Abstract. Ice temperature profiles from the Greenland Sheet contain information on deformation history, past climates and recent warming. We present full-depth two drill sites a flow line passing through Swiss Camp, West Greenland. Numerical modeling reveals that ice temperatures are considerably higher than would be expected heat diffusion dissipation alone. The possible causes for this extra evaluated using Lagrangian model. model results reveal observations can explained with combination...
The Geoscience Laser Altimeter System (GLAS) aboard the National Aeronautics and Space Administration's Ice, Cloud, land Elevation Satellite (ICESat) collected data from early 2003 to late 2009 with specific goal of measuring ice-surface elevation changes. While precision GLAS instrumentation has been studied over its intended target (ice), accuracy only robustly estimated using independent (terrestrial nonlaser) methods salt flats. Here, we perform repeat high-precision Global Positioning...
Abstract. We have derived digital elevation models (DEMs) over the western part of Devon Ice Cap in Nunavut, Canada, using "swath processing" interferometric data collected by Cryosat between February 2011 and January 2012. With standard ESA (European Space Agency) SARIn (synthetic aperture radar interferometry) level 2 (L2) product, mode is used to map cross-track position "point-of-closest-approach" (POCA) sloping glacial terrain. However, this work we explore extent which phase returns...
Abstract Accumulation is a key parameter governing the mass balance of Greenland ice sheet. Several studies have documented spatial variability accumulation over wide scales, primarily using point data, remote sensing or modeling. Direct measurements spatially extensive, detailed profiles in Greenland, however, are rare. We used 400 MHz ground-penetrating radar along 1009 km route Inland Traverse from Thule to Summit during April and May 2011, image continuous internal reflecting horizons....
Abstract. The rapid drainage of supraglacial lakes introduces large pulses meltwater to the subglacial environment and creates moulins, surface-to-bed conduits for future melt. Introduction water system has been shown affect ice flow, modeling suggests that variability in supply delivery subsurface play an important role development hydrologic its ability enhance or mitigate flow. We developed a fully automated method tracking drainages (> 0.125 km2) perennial applied it 10 yr time series...
Abstract Remote sensing observations and climate models indicate that the Greenland Ice Sheet (GrIS) has been losing mass since late 1990s, mostly due to enhanced surface melting from rising summer temperatures. However, in situ observational records of GrIS melt rates over recent decades are rare. Here we develop a record frozen meltwater west percolation zone preserved seven firn cores. Quantifying ice layer distribution as feature percentage (MFP), find significant increases MFP...
Abstract. High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of patterns relevant for future projections. Here, we present data from a new, annually dated ice core record eastern Ross Sea, named Roosevelt Island Climate Evolution (RICE) core. Comparison this with reanalysis 1979–2012 interval shows that RICE reliably captures temperature and snow precipitation variability in region. Trends over past 2700 years are shown be distinct...
Abstract We developed a multi-frequency, multi-Global Navigation Satellite System (GNSS) positioning instrument optimized for autonomous applications in the cryosphere. At lower power requirements and fraction of cost weight compared to commercially available options, this simplifies field usage associated logistics. In paper, we assess several baseline aspects performance polar environment relative geodetic receivers commonly used glaciological applications. Evaluations precision accuracy...
Abstract. A series of NASA airborne lidars have been used in support satellite laser altimetry missions. These altimeters deployed for instrument development, spaceborne data validation, and to bridge the gap between We from ground-based Global Positioning System (GPS) surveys an 11 km long track near Summit Station, Greenland, assess surface–elevation bias measurement precision three including Airborne Topographic Mapper (ATM), Land, Vegetation, Ice Sensor (LVIS), Multiple Altimeter Beam...
Abstract Tidewater glacier calving provides the most direct mechanism of ice transfer from land to ocean. However, physical melt processes influencing remain challenging constrain. In this study we focus on rates at Kongsbreen, a tidewater in Svalbard, due three mechanisms submarine melt: (1) free convection, (2) horizontal fjord circulation, and (3) meltwater discharge. To calculate an overall rate, measure velocity terminus change using Sentinel imagery. We discharge mooring data for...
Abstract The impact of summer surface melt on Greenland Ice Sheet dynamics is modulated by the state subglacial hydrologic system. Studies ice motion indicate that efficiency system increases over season, decreasing sensitivity to inputs. However, behavior complex and some characteristics are still poorly constrained. Here we investigate coevolution hydrology in Pâkitsoq region western during 2011 season. We analyze measurements from 11 Global Positioning System stations, which derive...
Abstract. The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is critical interest to scientists and general public context future sea-level rise. An improved understanding temporal spatial variability snow accumulation will reduce uncertainties GrIS models improve projections Greenland's contribution rise, currently estimated at 0.089 ± 0.03 m by 2100. Here we analyze 25 NASA Operation IceBridge radar flights totaling > 17 700 km from 2013 2014 determine dry...
We present data from the European Space Agency's Airborne SAR/Interferometric Radar Altimeter System (ASIRAS), flown during CryoVex 2004 field calibration/validation campaign, and new, high‐resolution depth profiles of snow density measured in by neutron scattering. combine these to calculate internal reflecting horizons ASIRAS data. The high resolution allow us identify annual layers profile, correlate their peaks with horizons. use thickness combined profile determine spatial temporal...
Abstract Field measurements of shallow borehole temperatures in firn across the northern Greenland ice sheet are collected during May 2013. Sites first measured 1952–1955 revisited, showing long‐term trends temperature. Results indicate a pattern substantial warming (up to +5.7°C) at midlevel elevations (1400–2500 m) and little temperature change high (>2500 m). We find that latent heat transport into due meltwater percolation drives observed warming. Modeling shows is stored depth for...
Marine-terminating outlet glaciers discharge mass through iceberg calving, submarine melting, and meltwater run-off. While calving can be quantified by in situ remote-sensing observations, run-off, the subglacial transport of meltwater, melting are not well constrained due to inherent difficulties observing proglacial environments at tidewater glaciers. Remote-sensing measurements surface sediment plumes, their suspended concentration (SSC), have been used as a proxy for glacier However,...
ABSTRACT Marine-terminating outlet glaciers discharge most of the Greenland ice sheet's mass through frontal ablation and meltwater runoff. While calving can be estimated by in situ remote sensing observations, submarine melting subglacial transport are more challenging to quantify. Here we investigate hydrology Rink Isbræ, a fast-flowing West tidewater glacier, using time-lapse photography, modeled runoff estimates daily satellite imagery from 2007 2011. We find that sediment plumes appear...
Abstract. The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is critical interest context future sea level rise. Increased melting GrIS percolation zone due to atmospheric over past several decades has led increased loss at lower elevations. Previous studies have hypothesized that this accompanied by precipitation increase, as would be expected from Clausius–Clapeyron relationship, compensating for some melt-induced throughout western GrIS. This study tests hypothesis...
Abstract Microstructures, including crystallographic fabric, within the margin of streaming ice can exert strong control on flow dynamics. To characterize a natural setting, we retrieved three cores, two which reached bed, from flank Jarvis Glacier, eastern Alaska Range, Alaska. The core sites lie ~1 km downstream source, with abundant water present in extracted cores and at base glacier. All exhibit dipping layers, combination debris bands bubble-free domains. Grain sizes coarsen average...
Abstract Air–snow transfer processes impact both ice-core interpretation and exchange affecting atmospheric chemistry. An understanding of seasonal differences in the character surface snow will facilitate evaluation possible preferential reactive chemical species. Both diffusive advective (ventilation) can serve to alter physical, isotopic firn. In this paper, we examine measurements roughness over course a year at Summit, Greenland, implications for firn ventilation. At during winter-over...