The ASTIS database cites the following 8 publication(s) by Shawn Marshall. Publications are listed from newest to oldest. Please tell us about publications that are not yet cited in ASTIS.

Isotope thermometry in melt-affected ice cores   /   Moran, T.   Marshall, S.J.   Sharp, M.J.
(Journal of geophysical research, v.116, F02010, 2011, 10 p., ill., maps)
ASTIS record 74939.
Languages: English
Web: doi:10.1029/2010JF001738
Libraries: ACU

A statistically significant relationship is observed between stable water isotopes (delta 18O) and melt amounts in a melt-affected firn core (SSummit) taken from the Prince of Wales Icefield, Ellesmere Island, Canada. By contrast, a low-melt firn core taken from a higher-elevation, higher-latitude location on the same icefield shows no relationship between these variables. We interpret this as evidence for meltwater-induced isotopic enrichment at SSummit. A percent melt-based correction slope is applied to isotopic values from SSummit. Uncorrected and corrected temperature records derived from the raw and corrected delta 18O values are compared to bias-corrected temperature data from the NCEP Reanalysis. Improvements are observed in the isotopic reconstruction of SSummit annual precipitation-weighted temperatures when we correct for meltwater enrichment, with a reduction from +0.6°C to 0.0°C in the mean annual error and a decrease in root-mean-square error from 1.8°C to 1.6°C. The correction factor appears to overcorrect isotopic modification during high melt years such as 1999, during which SSummit experienced nearly 70% more melt than the average from 1975 to 2000. Excluding 1999 data from the correction analysis results in a slight reduction in mean absolute error from 1.4°C to 1.3°C. These results suggest that melt-induced isotopic modification cannot be corrected in very high melt years. (Au)

F, A, E
Atmospheric temperature; Cores; Density; Firn; Glacial stratigraphy; Glaciers; Isotopes; Measurement; Oxygen-18; Precipitation (Meteorology); Quality assurance; Snow metamorphism; Snowmelt; Temperature; Thermal regimes

Prince of Wales Icefield, Nunavut

Glaciological reconstruction of the Laurentide Ice Sheet : physical processes and modelling challenges   /   Marshall, S.J.   Tarasov, L.   Clarke, G.K.C.   Peltier, W.R.
(Canadian journal of earth sciences, v. 37, no. 5, May 2000, p. 769-793, ill., maps)
ASTIS record 48496.
Languages: English
Web: doi:10.1139/cjes-37-5-769
Libraries: ACU

Current understanding of Pleistocene ice-sheet history is based on collective inferences from three separate avenues of study: (1) the geologic and paleoceanographic records, (2) the isostatic record, and (3) the behaviour of contemporary glaciers and ice sheets. The geologic record provides good constraint on the areal extent of former ice sheets, while isostatic deflection patterns provide important information about late-glacial ice-sheet thickness. The picture emerging from geologic and isostatic deductions is suggestive of a thin and mobile Laurentide Ice Sheet relative to present-day Greenland and Antarctica. We model Laurentide Ice Sheet evolution through a glacial cycle to explore the glaciological mechanisms that are required to replicate the geologic and isostatic evidence. A number of glaciological processes important to the ice-sheet evolution are not fully understood, including marine-based ice dynamics, iceberg calving, rheologic properties of ice, and basal flow dynamics. We present a spectrum of glacial cycle simulations with different treatments of poorly constrained physical processes. We conclude that glaciological model reconstructions can only be reconciled with the late-glacial geologic record of a thin, low-sloping Laurentide Ice Sheet by invoking (1) extremely deformable ice, (2) widespread basal flow, or (3) paleoclimate-ice-sheet fluctuations which give last glacial maximum ice sheets that are far from equilibrium. (Au)

B, F, A, J, E, G
Atmospheric temperature; Calving (Ice); Deglaciation; Effects of climate on ice; Effects of ice on climate; Geology; Glaciation; Glaciology; Ice sheets; Icebergs; Laurentide Ice Sheet; Mathematical models; Palaeoclimatology; Palaeogeography; Pleistocene epoch; Precipitation (Meteorology); Sea ice; Sea level; Temperature

G10, G08, G15, G081
Antarctic regions; Canada; Canadian Arctic; Greenland; Hudson Bay region; Hunker Creek region, Yukon; North American Arctic; Nunavik, Québec

Modeling North American freshwater runoff through the last glacial cycle   /   Marshall, S.J.   Clarke, G.K.C.
(Quaternary research, v. 52, no. 3, Nov. 1999, p. 300-315, ill., maps)
ASTIS record 48770.
Languages: English
Web: doi:10.1006/qres.1999.2079
Libraries: ACU

The Northern Hemisphere ice sheets decayed rapidly during deglacial phases of the ice-age cycle, producing meltwater fluxes that may have been of sufficient magnitude to perturb oceanic circulation. The continental record of ice-sheet history is more obscured during the growth and advance of the last great ice sheets, ca. 120,000-20,000 yr B.P., but ice cores tell of high-amplitude, millennial-scale climate fluctuations that prevailed throughout this period. These climatic excursions would have provoked significant fluctuation of ice-sheet margins and runoff variability whenever ice sheets extended to mid-latitudes, giving a complex pattern of freshwater delivery to the oceans. A model of continental surface hydrology is coupled with an ice-dynamics model simulating the last glacial cycle in North America. Meltwater discharged from ice sheets is either channeled down continental drainage pathways or stored temporarily in large systems of proglacial lakes that border the retreating ice-sheet margin. The coupled treatment provides quantitative estimates of the spatial and temporal patterns of freshwater flux to the continental margins. Results imply an intensified surface hydrological environment when ice sheets are present, despite a net decrease in precipitation during glacial periods. Diminished continental evaporation and high levels of meltwater production combine to give mid-latitude runoff values that are highly variable through the glacial cycle, but are two to three times in excess of modern river fluxes; drainage to the North Atlantic via the St. Lawrence, Hudson, and Mississippi River catchments averages 0.356 Sv for the period 60,000-10,000 yr B.P., compared to 0.122 Sv for the past 10,000 yr. High-amplitude meltwater pulses to the Gulf of Mexico, North Atlantic, and North Pacific occur throughout the glacial period, with ice-sheet geometry controlling intricate patterns of freshwater routing variability. Runoff from North America is staged in the final deglaciation, with a stepped sequence of pulses through the Mississippi, St. Lawrence, Arctic, and Hudson Strait drainages. (Au)

A, F, D, E, B
Deglaciation; Drainage; Glacial epoch; Glacial melt waters; Glacier lakes; Hydrology; Ice sheets; Laurentide Ice Sheet; Mass balance; Mathematical models; Ocean currents; Palaeoclimatology; Palaeohydrology; Rivers; Runoff; Spatial distribution; Thickness; Topography

G0812, G081, G0815, G0826, G0825
Baffin Bay-Davis Strait; Canada; Canadian Arctic; Columbia River, Washington; Hudson Strait, Nunavut/Québec; Mackenzie River, N.W.T.; Mississippi River, United States; North America; St. Lawrence River, Canada/United States

Geologic and topographic controls on fast flow in the Laurentide and Cordilleran Ice Sheets   /   Marshall, S.J.   Clarke, G.K.C.   Dyke, A.S.   Fisher, D.A.
(Journal of geophysical research, v.101, no. B 8, Aug. 10, 1996, p.17,827-17,839, ill., maps)
ASTIS record 52540.
Languages: English
Web: doi:10.1029/96JB01180
Libraries: ACU

Ice streams are fast flowing arteries which play a vital role in the dynamics and mass balance of present-day ice sheets. Although not fully understood, fast flow dynamics are intimately coupled with geologic, topographic, thermal, and hydrologic conditions of the underlying bed. These are difficult observables beneath contemporary ice sheets, hindering elucidation of the processes which govern ice stream behavior. For past ice sheets the problem is antithetic. Geologic evidence of former ice streams exists, but spatial and temporal histories are uncertain; however, detailed knowledge of bed geology and topography is available in many places. We take advantage of this information to compile terrain characteristics relevant to fast flow dynamics in the Laurentide and Cordilleran Ice Sheets. Using seed points where fast flowing Wisconsinan ice has been geologically inferred, discriminant analysis of a suite of North American geologic and topographic properties yields a concise measure of ice-bed coupling strength. Our analysis suggests that the interior plains and continental shelf regions of North America have low basal coupling relative to areas of variable relief or exposed bedrock in the Cordillera and on the Canadian Shield. We conclude that the interior plains and continental shelves are both topographically and geologically predisposed to large-scale basal flows (i.e., ice streams or surge lobes). This result holds independent of whether the mechanism of fast flow is sediment deformation or decoupled sliding over the bed. (Au)

F, B, A
Continental shelves; Deformation; Flow; Geology; Geomorphology; Glacial deposits; Glacial epoch; Glacial landforms; Glacier surges; Glacier variations; Hydrology; Ice sheets; Laurentide Ice Sheet; Mass balance; Mathematical models; Mechanical properties; Melting; Physical geography; Sediments (Geology); Spatial distribution; Temporal variations; Thermal regimes; Thickness; Topography; Velocity

G08, G081, G10
Canada; Canadian Arctic; Greenland; United States

Ice age cycles : questions and answers under the glacier = Les cycles glaciaires : les questions et réponses trouvés sous le glacier   /   Marshall, S.J.   Clarke, G.K.C.
In: Fourth National Student Conference on Northern Studies : Conference programme and abstracts, Government Conference Centre, Ottawa, November 26-27, 1994 = Quatrième conférence nationale des étudiants en études nordiques : Calendrier des événements et sommaires, Centre de Conférence du Gouvernement, Ottawa, du 26 au 27 novembre 1994. - Ottawa : ACUNS, 1994, p. [72]
Abstract only.
ASTIS record 36664.
Languages: English and French
Libraries: ACU

The traditional view of Ice Age cycles invokes stately accumulation of ice masses in response to climatic forcing. Ice sheets creep steadily southward from northern highland source regions, followed by rapid meltback and retreat at glacial terminations. Mounting geomorphic, palynologic, paleoceanographic, and ice core evidence suggests that ice sheets were much more dynamic, with rapid and episodic fluctuations dictated by internal and subglacial flow instabilities. Fast glacier flow results from decoupled sliding over the ice sheet bed or from failure and deformation of subglacial sediments. Each flow mechanism is driven at the bed and is governed by geology, topography, and by thermal and hydrologic conditions beneath the ice. Improved understanding of ice sheet evolution requires better understanding of these processes and controls. We are undertaking a three-pronged attack to this end: (1) Field study of subglacial processes beneath a surge-type glacier in the St. Elias Mountains, Yukon Territory. (2) Geological reconstructions of basal environment and processes formerly active beneath the Laurentide Ice Sheet which covered Canada. The Laurentide bed is accessible and preserves many hints to hydrologic and ice-dynamic histories. (3) Numerical modelling of the Laurentide Ice Sheet to test subglacial process models. We have developed a comprehensive model which includes ice sheet dynamics, ice sheet and ground thermodynamics, and detailed bed geology and topography. The model is constrained by reconstructions and observational insights. This integrated approach promises to improve our understanding of basal process physics and past behaviour of the Laurentide Ice Sheet. (Au)

A, F
Deglaciation; Flow; Glacial epoch; Glacier surges; Glacier variations; Glaciology; Ice sheets; Laurentide Ice Sheet; Mathematical models; Thermodynamics

St. Elias Mountains, Alaska/British Columbia/Yukon

Toward in-situ building R-value measurement   /   Flanders, S.N.   Marshall, S.J.
Hanover, N.H. : Cold Regions Research and Engineering Laboratory, 1984.
iv, 13 p. : figures, tables ; 28 cm.
(CRREL report, 84- 1)
ASTIS record 14057.
Languages: English
Libraries: ACU NFSMO

A technique for measuring the thermal resistance (R-value) of large areas of building envelope is under development. It employs infrared thermography to locate radiant temperature extremes on a building surface and to provide a map of normalized temperature values for interpolation between locations. Contact thermal sensors (thermocouples for temperature and thermopiles for heat flow) are used to calculate the R-value at specific locations by summing the output from each sensor until the ratio between temperature difference (Delta T) from inside to outside surface and heat flow converges to a constant value. R-value measurements of a wood frame insulated wall were within 13% of the expected theoretical value. Similar measurements of a masonry wall were 31 and 43% less than expected. Experimentation demonstrated that a large Delta T was the single most important variable affecting accuracy and speed of convergence. Thermal guards around heat flow sensors were of little value, according to both experimentation and computer simulation. Attempts to match the absorptivity of sensors with their surroundings may have been insufficient to diminish about 10% of the remaining error in measurement. Lateral heat flow and convection may have been significant problems for accuracy in the masonry construction. Currently, an investigator cannot rely on the literature for guidance in assessing the limitations on accuracy for in-situ building R-value measurement. (Au)

Heat transmission; Insulating materials; Thermal properties


Roof response to icing conditions   /   Lane, J.W.   Marshall, S.J.   Munis, R.H.
Hanover, N.H. : U.S. Army, CRREL, 1979.
vi, 40p. : ill., photos., tables ; 28cm.
(CRREL report, 79- 17)
ASTIS record 2926.
Languages: English
Libraries: ACU NFSMO

Six test roofs of two different slopes - 16.3° and 39.8°, and three different roof coverings - asphalt shingles, cedar shingles, and corrugated aluminum sheeting, were constructed at USACRREL ... and were instrumented with thermocouples, heat flow meters, and calibrated gutters. ... It was found that eave icing is a sensitive function of the slope, roof covering composition, and solar radiation. The effects of wind were not investigated; the data were screened to remove all information corresponding to windspeeds over 8 km/h. ... (Au)

M, E
Icing; Roofs


Infrared thermography of buildings : 1977 Coast Guard survey   /   Marshall, S.J.
Hanover, New Hampshire : CRREL, 1979.
iv, 40p. : ill., figures, tables ; 27cm.
(Special report - U.S. Army Cold Regions Research and Engineering Laboratory, 79- 20)
Cover title.
ASTIS record 2723.
Languages: English
Libraries: ACU

An IRTB (infrared thermography of buildings) field survey, producing 631 thermograms, 127 photographs, and weather data, was conducted during a 14-day study of 10 Coast Guard stations .... This report discusses how the survey was initiated and performed .... One-hundred and twenty selected thermograms and photographs in this report illustrate many types of heat loss and compare thermally ineffective doors and windows with units designated as standards for thermal effectiveness. Radiator heat leakage through walls, mottled moisture patterns on brick walls, infiltration patterns on glass, and poorly covered openings are illustrated. Thermograms of severe heat losses through glass doors, glass transoms, and glass wall panels are also included, and several solutions for individual heat loss problems, such as fiberglass garage doors and porcelain insulated panels, are suggested. ... (Au)

Heat transmission; Heating


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