Shawn Marshall | University of Calgary (original) (raw)
Papers by Shawn Marshall
Journal of Geoscience Education, Mar 1, 2009
Journal of Geophysical Research, 2005
Understanding past climate over Antarctica and evaluating the isotopic composition of its large i... more Understanding past climate over Antarctica and evaluating the isotopic composition of its large ice sheets remain challenges to elucidate for the paleoclimatologists' community. The present work combines glaciological models of various degrees of complexity to estimate these quantities from recently drilled ice cores (Vostok, Dome C, Byrd...). A 1-D deposition model and a 2-D flow model are used in inverse
In the future, Arctic warming and the melting of polar glaciers will be considerable, but the mag... more In the future, Arctic warming and the melting of polar glaciers will be considerable, but the magnitude of both is uncertain. We used a global climate model, a dynamic ice sheet model, and paleoclimatic data to evaluate Northern Hemisphere high-latitude warming and its impact on Arctic icefields during the Last Interglaciation. Our simulated climate matches paleoclimatic observations of past warming, and the combination of physically based climate and ice-sheet modeling with ice-core constraints indicate that the Greenland Ice Sheet and other circum-Arctic ice fields likely contributed 2.2 to 3.4 meters of sea-level rise during the Last Interglaciation.
Hydrology and Earth System Sciences, 2014
A proper energy balance calculation of snow and ice melt is difficult to carry out in ice sheet m... more A proper energy balance calculation of snow and ice melt is difficult to carry out in ice sheet models due to the need for detailed meteorological data (i.e. wind conditions, cloud cover, etc.) that are unavailable for the past and too complex and spatially variable to be extracted from climate models. Ice sheet models therefore resort to more simple positive degree day (PDD) melt relationships to parameterize snow and ice melt from air temperature inputs for mass balance calculations. However, the PDD parameters that have been developed for use in ice sheet models are based on studies done in Greenland and the Canadian Arctic where temperatures are relatively low and radiation regimes different than those at lower latitudes. This becomes a problem in applications to the former Laurentide ice sheet, which was in radiation and temperature conditions possibly much different than those in which present relationships were established. The work presented here seeks to remedy the above pr...
Geophysical Monograph Series, 2000
Seismic studies and coring of proglacial lake Hvítárvatn, central Iceland, have revealed a detail... more Seismic studies and coring of proglacial lake Hvítárvatn, central Iceland, have revealed a detailed sedimentological history from which Holocene environmental conditions can be interpreted. These records indicate decisive shifts in sediment provenance over the last 10,000 years, which in turn provide constraints on the distribution and activity of ice in the Hvítárvatn catchment. The emerging interpretation is that the Hvítárvatn catchment was ice-free in the early Holocene, with Langjökull ice cap reaching its Holocene maximum during the Little Ice Age. To assess the validity of this interpretation from a glaciological standpoint, we use numerical models of ice dynamics and hydrology to investigate the climatic conditions under which the proposed glacial history is possible. The structure of temporal fluctuations in air temperature through the Holocene are taken from the NGRIP oxygen isotope record and referenced to a spatially-resolved 1961--1990 temperature map of the area. A ref...
Journal of Glaciology
The continued use of the positive degree-day (PDD) method to predict ice-sheet melt is generally ... more The continued use of the positive degree-day (PDD) method to predict ice-sheet melt is generally favoured over surface energy-balance methods partly due to the computational efficiency of the algorithm and the requirement of only one input variable (temperature). In this paper, we revisit some of the assumptions governing the application of the PDD method. Using hourly temperature data from the GC-Net network we test the assumption that monthly PDD total (PDDM) can be represented by a Gaussian distribution with fixed standard deviation of monthly temperature (σ M). The results presented here show that the common assumption of fixed σ M does not hold, and that σ M may be represented more accurately as a quadratic function of average monthly temperature. For Greenland, the mean absolute error in predicting PDDM using our methodology is 3.9°C d, representing a significant improvement on current methods (7.8°C d, when σ M = 4.5°C). Over a range of glaciated settings, our method reproduc...
Quaternary International, 2002
Glacier Science and Environmental Change, 2006
This chapter focuses on the coupling of glacier and climate models for simulation of glacier and ... more This chapter focuses on the coupling of glacier and climate models for simulation of glacier and icefield response to climate change. Sections 32.2 and 32.3 summarize glacier mass balance and ice dynamics considerations, concentrating on concepts that are central to ...
Encyclopedia of Sustainability Science and Technology, 2012
Annals of Glaciology, 2014
ABSTRACT Alberta's Bow River has its headwaters in the glaciated eastern slopes of the Ca... more ABSTRACT Alberta's Bow River has its headwaters in the glaciated eastern slopes of the Canadian Rockies and is a major source of water in southern Alberta. Glacial retreat, declining snowpacks and increased water demand are all expected in the coming century, yet there are relatively few studies focusing on quantifying glacial meltwater in the Bow River. We develop a new radiation–temperature melt model for modelling distributed glacier mass balance and runoff in the Bow River basin. The model reflects physical processes through the incorporation of near-surface air temperature and absorbed radiation, while avoiding problems of collinearity through the use of a radiation-decorrelated temperature index. The model is calibrated at Haig Glacier in the southern portion of the basin and validated at Haig and Peyto Glaciers. Application of the model to the entire Bow River basin for 2000–09 shows glacier ice melt is equivalent to 3% of annual discharge in Calgary on average. Modelled ice melt in August is equal to 8–20% of the August Bow River discharge in Calgary. This emphasizes the importance of glacier runoff to late-summer streamflow in the region, particularly in warm, dry years.
Encyclopedia of Earth Sciences Series, 2011
Science (New York, N.Y.), Jan 22, 2014
Nature, Jan 6, 2000
During the last interglacial period (the Eemian), global sea level was at least three metres, and... more During the last interglacial period (the Eemian), global sea level was at least three metres, and probably more than five metres, higher than at present. Complete melting of either the West Antarctic ice sheet or the Greenland ice sheet would today raise sea levels by 6-7 metres. But the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the West Antarctic ice sheet, with model studies attributing only 1-2 m of sea-level rise to meltwater from Greenland. This result was considered consistent with ice core evidence, although earlier work had suggested a much reduced Greenland ice sheet during the last interglacial period. Here we reconsider the Eemian evolution of the Greenland ice sheet by combining numerical modelling with insights obtained from recent central Greenland ice-core analyses. Our results suggest that the Greenland ice sheet was considerably smaller and steeper during the Eemian, and plausibly contributed 4-5.5...
Developments in Quaternary Sciences, 2003
Journal of Geoscience Education, Mar 1, 2009
Journal of Geophysical Research, 2005
Understanding past climate over Antarctica and evaluating the isotopic composition of its large i... more Understanding past climate over Antarctica and evaluating the isotopic composition of its large ice sheets remain challenges to elucidate for the paleoclimatologists' community. The present work combines glaciological models of various degrees of complexity to estimate these quantities from recently drilled ice cores (Vostok, Dome C, Byrd...). A 1-D deposition model and a 2-D flow model are used in inverse
In the future, Arctic warming and the melting of polar glaciers will be considerable, but the mag... more In the future, Arctic warming and the melting of polar glaciers will be considerable, but the magnitude of both is uncertain. We used a global climate model, a dynamic ice sheet model, and paleoclimatic data to evaluate Northern Hemisphere high-latitude warming and its impact on Arctic icefields during the Last Interglaciation. Our simulated climate matches paleoclimatic observations of past warming, and the combination of physically based climate and ice-sheet modeling with ice-core constraints indicate that the Greenland Ice Sheet and other circum-Arctic ice fields likely contributed 2.2 to 3.4 meters of sea-level rise during the Last Interglaciation.
Hydrology and Earth System Sciences, 2014
A proper energy balance calculation of snow and ice melt is difficult to carry out in ice sheet m... more A proper energy balance calculation of snow and ice melt is difficult to carry out in ice sheet models due to the need for detailed meteorological data (i.e. wind conditions, cloud cover, etc.) that are unavailable for the past and too complex and spatially variable to be extracted from climate models. Ice sheet models therefore resort to more simple positive degree day (PDD) melt relationships to parameterize snow and ice melt from air temperature inputs for mass balance calculations. However, the PDD parameters that have been developed for use in ice sheet models are based on studies done in Greenland and the Canadian Arctic where temperatures are relatively low and radiation regimes different than those at lower latitudes. This becomes a problem in applications to the former Laurentide ice sheet, which was in radiation and temperature conditions possibly much different than those in which present relationships were established. The work presented here seeks to remedy the above pr...
Geophysical Monograph Series, 2000
Seismic studies and coring of proglacial lake Hvítárvatn, central Iceland, have revealed a detail... more Seismic studies and coring of proglacial lake Hvítárvatn, central Iceland, have revealed a detailed sedimentological history from which Holocene environmental conditions can be interpreted. These records indicate decisive shifts in sediment provenance over the last 10,000 years, which in turn provide constraints on the distribution and activity of ice in the Hvítárvatn catchment. The emerging interpretation is that the Hvítárvatn catchment was ice-free in the early Holocene, with Langjökull ice cap reaching its Holocene maximum during the Little Ice Age. To assess the validity of this interpretation from a glaciological standpoint, we use numerical models of ice dynamics and hydrology to investigate the climatic conditions under which the proposed glacial history is possible. The structure of temporal fluctuations in air temperature through the Holocene are taken from the NGRIP oxygen isotope record and referenced to a spatially-resolved 1961--1990 temperature map of the area. A ref...
Journal of Glaciology
The continued use of the positive degree-day (PDD) method to predict ice-sheet melt is generally ... more The continued use of the positive degree-day (PDD) method to predict ice-sheet melt is generally favoured over surface energy-balance methods partly due to the computational efficiency of the algorithm and the requirement of only one input variable (temperature). In this paper, we revisit some of the assumptions governing the application of the PDD method. Using hourly temperature data from the GC-Net network we test the assumption that monthly PDD total (PDDM) can be represented by a Gaussian distribution with fixed standard deviation of monthly temperature (σ M). The results presented here show that the common assumption of fixed σ M does not hold, and that σ M may be represented more accurately as a quadratic function of average monthly temperature. For Greenland, the mean absolute error in predicting PDDM using our methodology is 3.9°C d, representing a significant improvement on current methods (7.8°C d, when σ M = 4.5°C). Over a range of glaciated settings, our method reproduc...
Quaternary International, 2002
Glacier Science and Environmental Change, 2006
This chapter focuses on the coupling of glacier and climate models for simulation of glacier and ... more This chapter focuses on the coupling of glacier and climate models for simulation of glacier and icefield response to climate change. Sections 32.2 and 32.3 summarize glacier mass balance and ice dynamics considerations, concentrating on concepts that are central to ...
Encyclopedia of Sustainability Science and Technology, 2012
Annals of Glaciology, 2014
ABSTRACT Alberta's Bow River has its headwaters in the glaciated eastern slopes of the Ca... more ABSTRACT Alberta's Bow River has its headwaters in the glaciated eastern slopes of the Canadian Rockies and is a major source of water in southern Alberta. Glacial retreat, declining snowpacks and increased water demand are all expected in the coming century, yet there are relatively few studies focusing on quantifying glacial meltwater in the Bow River. We develop a new radiation–temperature melt model for modelling distributed glacier mass balance and runoff in the Bow River basin. The model reflects physical processes through the incorporation of near-surface air temperature and absorbed radiation, while avoiding problems of collinearity through the use of a radiation-decorrelated temperature index. The model is calibrated at Haig Glacier in the southern portion of the basin and validated at Haig and Peyto Glaciers. Application of the model to the entire Bow River basin for 2000–09 shows glacier ice melt is equivalent to 3% of annual discharge in Calgary on average. Modelled ice melt in August is equal to 8–20% of the August Bow River discharge in Calgary. This emphasizes the importance of glacier runoff to late-summer streamflow in the region, particularly in warm, dry years.
Encyclopedia of Earth Sciences Series, 2011
Science (New York, N.Y.), Jan 22, 2014
Nature, Jan 6, 2000
During the last interglacial period (the Eemian), global sea level was at least three metres, and... more During the last interglacial period (the Eemian), global sea level was at least three metres, and probably more than five metres, higher than at present. Complete melting of either the West Antarctic ice sheet or the Greenland ice sheet would today raise sea levels by 6-7 metres. But the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the West Antarctic ice sheet, with model studies attributing only 1-2 m of sea-level rise to meltwater from Greenland. This result was considered consistent with ice core evidence, although earlier work had suggested a much reduced Greenland ice sheet during the last interglacial period. Here we reconsider the Eemian evolution of the Greenland ice sheet by combining numerical modelling with insights obtained from recent central Greenland ice-core analyses. Our results suggest that the Greenland ice sheet was considerably smaller and steeper during the Eemian, and plausibly contributed 4-5.5...
Developments in Quaternary Sciences, 2003