Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
- Keyword
-
- 300 social sciences (1)
- Ablation zone (1)
- Boreholes (1)
- Brines (1)
- Chemistry (1)
-
- Climate change (1)
- Conduction (1)
- Dark (1)
- Deformation (1)
- Department of anthropology (1)
- Diffusivity (1)
- Dinaledi chamber (1)
- Dry ice (1)
- Ecosystem (1)
- Electrical resistivity (1)
- Electromagnetic phenomena (1)
- Electromagnetism (1)
- Fast-flow (1)
- Genomics and evolutionary biology (1)
- Geography (1)
- Geosciences (1)
- Glaciers (1)
- Gn (1)
- Groundwater (1)
- Habitats (1)
- Heat transfer (1)
- Hominin (1)
- Homo naledi (1)
- Ice (1)
- Ice and climate ice core (1)
Articles 1 - 13 of 13
Full-Text Articles in Physical Sciences and Mathematics
Mercury In Coniferous And Deciduous Upland Forests In Northern New England, Usa: Implications Of Climate Change, J. B. Richardson, A. J. Friedland
Mercury In Coniferous And Deciduous Upland Forests In Northern New England, Usa: Implications Of Climate Change, J. B. Richardson, A. J. Friedland
Dartmouth Scholarship
Climatic changes in the northeastern US are expected to cause coniferous stands to transition to deciduous stands over the next hundred years. Mercury (Hg) sequestration in forest soils may change as a result. In order to understand potential effects of such a transition, we studied aboveground vegetation and soils at paired coniferous and deciduous stands on eight mountains in Vermont and New Hampshire, USA.
Coastal Ice-Core Record Of Recent Northwest Greenland Temperature And Sea-Ice Concentration, Erich C. Osterberg, Robert L. Hawley, Gifford Wong, Ben Kopec, David Ferris, Jennifer Howley
Coastal Ice-Core Record Of Recent Northwest Greenland Temperature And Sea-Ice Concentration, Erich C. Osterberg, Robert L. Hawley, Gifford Wong, Ben Kopec, David Ferris, Jennifer Howley
Dartmouth Scholarship
Coastal ice cores provide an opportunity to investigate regional climate and sea-ice variability in the past to complement hemispheric-scale climate reconstructions from ice-sheet-interior ice cores. Here we describe robust proxies of Baffin Bay temperature and sea-ice concentration from the coastal 2Barrel ice core collected in the Thule region of northwest Greenland. Over the 1990–2010 record, 2Barrel annually averaged methanesulfonic acid (MSA) concentrations are significantly correlated with May–June Baffin Bay sea-ice concentrations and summer temperatures. Higher MSA is observed during warmer years with less sea ice, indicative of enhanced primary productivity in Baffin Bay. Similarly, 2Barrel annually averaged deuterium excess (d-excess) …
Homo Naledi, A New Species Of The Genus Homo From The Dinaledi Chamber, South Africa, Lee Berger, John Hawks, Darryl J. De Ruiter, Steve E. Churchill, Peter Schmid, Lucas Delezene, Tracy Kivell, Heather Garvin, Scott Williams, Jeremy Desilva
Homo Naledi, A New Species Of The Genus Homo From The Dinaledi Chamber, South Africa, Lee Berger, John Hawks, Darryl J. De Ruiter, Steve E. Churchill, Peter Schmid, Lucas Delezene, Tracy Kivell, Heather Garvin, Scott Williams, Jeremy Desilva
Dartmouth Scholarship
Homo naledi is a previously-unknown species of extinct hominin discovered within the Dinaledi Chamber of the Rising Star cave system, Cradle of Humankind, South Africa. This species is characterized by body mass and stature similar to small-bodied human populations but a small endocranial volume similar to australopiths. Cranial morphology of H. naledi is unique, but most similar to early Homo species including Homo erectus, Homo habilis or Homo rudolfensis. While primitive, the dentition is generally small and simple in occlusal morphology. H. naledi has humanlike manipulatory adaptations of the hand and wrist. It also exhibits a humanlike foot and lower …
Predicting Landscape-Scale Co 2 Flux At A Pasture And Rice Paddy With Long-Term Hyperspectral Canopy Reflectance Measurements, J. H. Matthes, S. H. Knox, C. Sturtevant, O. Sonnentag
Predicting Landscape-Scale Co 2 Flux At A Pasture And Rice Paddy With Long-Term Hyperspectral Canopy Reflectance Measurements, J. H. Matthes, S. H. Knox, C. Sturtevant, O. Sonnentag
Dartmouth Scholarship
Measurements of hyperspectral canopy reflectance provide a detailed snapshot of information regarding canopy biochemistry, structure and physiology. In this study, we collected 5 years of repeated canopy hyperspectral reflectance measurements for a total of over 100 site visits within the flux footprints of two eddy covariance towers at a pasture and rice paddy in northern California. The vegetation at both sites exhibited dynamic phenology, with significant interannual variability in the timing of seasonal patterns that propagated into interannual variability in measured hyperspectral reflectance. We used partial least-squares regression (PLSR) modeling to leverage the information contained within the entire canopy reflectance …
The Role Of Blowing Snow In The Activation Of Bromine Over First-Year Antarctic Sea Ice, R. M. Lieb-Lappen, R. W. Obbard
The Role Of Blowing Snow In The Activation Of Bromine Over First-Year Antarctic Sea Ice, R. M. Lieb-Lappen, R. W. Obbard
Dartmouth Scholarship
It is well known that during polar springtime halide sea salt ions, in particular Br-, are photochemically activated into reactive halogen species (e.g., Br and BrO), where they break down tropospheric ozone. This research investigated the role of blowing snow in transporting salts from the sea ice/snow surface into reactive bromine species in the air. At two different locations over first-year ice in the Ross Sea, Antarctica, collection baskets captured blowing snow at different heights. In addition, sea ice cores and surface snow samples were collected throughout the month-long campaign. Over this time, sea ice and surface snow …
The Role Of Damage And Recrystallization In The Elastic Properties Of Columnar Ice, Scott A. Snyder, Erland M. Schulson, Carl E. Renshaw
The Role Of Damage And Recrystallization In The Elastic Properties Of Columnar Ice, Scott A. Snyder, Erland M. Schulson, Carl E. Renshaw
Dartmouth Scholarship
Effects of damage on elastic properties were studied in columnar-grained specimens of freshwater and saline ice, subjected, at −10°C, to varying levels of inelastic strain. The ice was compressed uniaxially at constant strain rates up to 0.20 strain, which caused localized recrystallization and imparted damage in the form of non-propagating cracks. Damage was quantified in terms of dimensionless crack density, which, along with recrystallized area fraction, was determined from thin sections. The change in porosity due to stress-induced cracks served as another indicator of damage. Elastic properties were derived using P-wave and S-wave ultrasonic transmission velocities measured in across-column directions …
Resonance Of Relativistic Electrons With Electromagnetic Ion Cyclotron Waves, Richard Denton, K. Jordanova, J. Bortnik
Resonance Of Relativistic Electrons With Electromagnetic Ion Cyclotron Waves, Richard Denton, K. Jordanova, J. Bortnik
Dartmouth Scholarship
Relativistic electrons have been thought to more easily resonate with electromagnetic ion cyclotron (EMIC) waves if the total density is large. We show that, for a particular EMIC mode, this dependence is weak due to the dependence of the wave frequency and wave vector on the density. A significant increase in relativistic electron minimum resonant energy might occur for the H band EMIC mode only for small density, but no changes in parameters significantly decrease the minimum resonant energy from a nominal value. The minimum resonant energy depends most strongly on the thermal velocity associated with the field line motion …
Field Line Distribution Of Mass Density At Geostationary Orbit, Richard Denton, Kazue Takahashi, Jimyoung Lee, C.K. Zeitler, N.T. Wimer, E. Litscher, H.J. Singer, Kyungguk Min
Field Line Distribution Of Mass Density At Geostationary Orbit, Richard Denton, Kazue Takahashi, Jimyoung Lee, C.K. Zeitler, N.T. Wimer, E. Litscher, H.J. Singer, Kyungguk Min
Dartmouth Scholarship
The distribution of mass density along the field lines affects the ratios of toroidal (azimuthally oscillating) Alfv'{e}n frequencies, and given the ratios of these frequencies we can get information about that distribution. Here we assume the commonly used power law form for the field line distribution, rho_{m} = rho_{m,eq} ( L R_{E} /R )^alpha, where rho_{m,eq} is the value of the mass density rho_{m} at the magnetic equator, L is the L shell, R_{E} is the Earth's radius, R is the geocentric distance to a point on the field line, and alpha is the power law coefficient. Positive values of …
Deep Groundwater And Potential Subsurface Habitats Beneath An Antarctic Dry Valley, J. A. Mikucki, E. Auken, S. Tulaczyk, R. A. Virginia, C. Schamper, K. I. Sørensen, P. T. Doran, H. Dugan, N Foley
Deep Groundwater And Potential Subsurface Habitats Beneath An Antarctic Dry Valley, J. A. Mikucki, E. Auken, S. Tulaczyk, R. A. Virginia, C. Schamper, K. I. Sørensen, P. T. Doran, H. Dugan, N Foley
Dartmouth Scholarship
The occurrence of groundwater in Antarctica, particularly in the ice-free regions and along the coastal margins is poorly understood. Here we use an airborne transient electromagnetic (AEM) sensor to produce extensive imagery of resistivity beneath Taylor Valley. Regional- scale zones of low subsurface resistivity were detected that are inconsistent with the high resistivity of glacier ice or dry permafrost in this region. We interpret these results as an indication that liquid, with sufficiently high solute content, exists at temperatures well below freezing and considered within the range suitable for microbial life. These inferred brines are widespread within permafrost and extend …
Reconstructing Thermal Properties Of Firn At Summit, Greenland, From A Temperature Profile Time Series, Alexandra L. Giese, Robert L. Hawley
Reconstructing Thermal Properties Of Firn At Summit, Greenland, From A Temperature Profile Time Series, Alexandra L. Giese, Robert L. Hawley
Dartmouth Scholarship
We have constrained the value for thermal diffusivity of near-surface snow and firn at Summit Station, Greenland, using a Fourier-type analysis applied to hourly temperature measurements collected from eight thermistors in a closed-off, air-filled borehole between May 2004 and July 2008. An implicit, finite-difference method suggests that a bulk diffusivity of ∼25 ± 3m2 a−1 is the most reasonable for representing macroscale heat transport in the top 30 m of firn and snow. This value represents an average diffusivity and, in a conduction-only model, generates temperature series whose phase shifts with depth most closely match those of the Summit borehole …
Heat Sources Within The Greenland Ice Sheet: Dissipation, Temperate Paleo-Firn And Cryo-Hydrologic Warming, M. P. Lüthi, C. Ryser, L. C. Andrews, G. A. Catania, M. Funk, R. L. Hawley
Heat Sources Within The Greenland Ice Sheet: Dissipation, Temperate Paleo-Firn And Cryo-Hydrologic Warming, M. P. Lüthi, C. Ryser, L. C. Andrews, G. A. Catania, M. Funk, R. L. Hawley
Dartmouth Scholarship
Ice temperature profiles from the Greenland Ice Sheet contain information on the deformation history, past climates and recent warming. We present full-depth temperature profiles from two drill sites on a flow line passing through Swiss Camp, West Greenland. Numerical modeling reveals that ice temperatures are considerably higher than would be expected from heat diffusion and dissipation alone. The possible causes for this extra heat are evaluated using a Lagrangian heat flow model. The model results reveal that the observations can be explained with a combination of different processes: enhanced dissipation (strain heating) in ice-age ice, temperate paleo-firn, and cryo-hydrologic warming …
Impact Of Spatial Aliasing On Sea-Ice Thickness Measurements, Cathleen Geiger, Hans-Reinhard Müller, Jesse P. Samluk, E Rachel Bernstein, Jacqueline Richter-Menge
Impact Of Spatial Aliasing On Sea-Ice Thickness Measurements, Cathleen Geiger, Hans-Reinhard Müller, Jesse P. Samluk, E Rachel Bernstein, Jacqueline Richter-Menge
Dartmouth Scholarship
We explore spatial aliasing of non-Gaussian distributions of sea-ice thickness. Using a heuristic model and >1000 measurements, we show how different instrument footprint sizes and shapes can cluster thickness distributions into artificial modes, thereby distorting frequency distribution, making it difficult to compare and communicate information across spatial scales. This problem has not been dealt with systematically in sea ice until now, largely because it appears to incur no significant change in integrated thickness which often serves as a volume proxy. Concomitantly, demands are increasing for thickness distribution as a resource for modeling, monitoring and forecasting air–sea fluxes and growing human …
On The Uncertainty Of Sea-Ice Isostasy, Cathleen Geiger, Peter Wadhams, Hans-Reinhard Müller, Jacqueline Richter-Menge
On The Uncertainty Of Sea-Ice Isostasy, Cathleen Geiger, Peter Wadhams, Hans-Reinhard Müller, Jacqueline Richter-Menge
Dartmouth Scholarship
During late winter 2007, coincident measurements of sea ice were collected using various sensors at an ice camp in the Beaufort Sea, Canadian Arctic. Analysis of the archived data provides new insight into sea-ice isostasy and its related R-factor through case studies at three scales using different combinations of snow and ice thickness components. At the smallest scale (<1 m; point scale), isostasy is not expected, so we calculate a residual and define this as �� (‘zjey’) to describe vertical displacement due to deformation. From 1 to 10 m length scales, we explore traditional isostasy and identify a specific sequence of thickness calculations which minimize freeboard and elevation uncertainty. An effective solution exists when the R-factor is allowed to vary: ranging from 2 to 12, with mean of 5.17, mode of 5.88 and skewed distribution. At regional scales, underwater, airborne and spaceborne platforms are always missing thickness variables from either above or below sea level. For such situations, realistic agreement is found by applying small-scale skewed ranges for the R-factor. These findings encourage a broader isostasy solution as a function of potential energy and length scale. Overall, results add insight to data collection strategies and metadata characteristics of different thickness products.