107 research outputs found
Hydrology and dynamics of a land-terminating Greenland outlet glacier
The purpose of this thesis is to investigate the hydrology and dynamics of a land-terminating
outlet glacier on the western margin of the Greenland Ice Sheet (GrIS).
The investigations are motivated by uncertainty about the effect of meltwater on
rates of ice flow in the GrIS and the possibility that hydrologically forced changes
in ice velocity might increase mass loss from the ice sheet significantly in response
to climate warming. The impact of meltwater on fluctuations in ice flow has been a
research focus for glaciologists studying Alpine and Arctic glaciers for decades. In these
settings, one of the main controls on the relationship between surface melting and ice
velocity is the structure of the subglacial drainage system, which evolves spatially and
temporally on a seasonal basis in response to inputs of meltwater from the glacier surface.
In this thesis we present three years of field observations of glacier velocity, surface
ablation and hydrology from a land-terminating glacier in west Greenland. These data
are supplemented by satellite data and the use of simple models to constrain surface
melting.
We find that hydrologically forced ice acceleration occurs each year along a 115
km transect, first at sites nearest the ice sheet margin and at locations further inland
following the onset of surface melting at higher elevations. At sites near the ice
sheet margin, the relationship between surface melting and ice velocity is not consistent
throughout the melt season, and ice velocity becomes less sensitive to inputs of meltwater
later in the summer. This is explained by development in the efficiency of the subglacial
drainage system, in a manner similar to Alpine glaciers. We perform a hydrological
study which indicates that an efficient subglacial drainage system expands upglacier
over the course of the melt season, in response to inputs of water from the ice sheet
surface. At higher elevation sites, however, thicker ice and colder temperatures mean
that it is harder to generate enough water to reach the ice-bed interface and this only
occurs once enough water has accumulated to propagate fractures through thick ice to
the bed. One mechanism which allows this is drainage of supraglacial lakes.
Inter-annual comparison shows that increased rates of annual ablation lead to higher
annual ice velocities. At high elevation sites (>1000 m), timing of drainage of meltwater
to the ice-bed interface appears to be the main control on the the overall magnitude of
summer acceleration. At lower elevations, although development in the structure of the subglacial drainage system limits the overall summer acceleration signal, short-term
variability in meltwater input can sustain high ice velocities even once the subglacial
drainage system has become channelised. Overall, the research presented in this thesis
suggests that hydrologically-forced acceleration can increase mass loss from the GrIS
in a warmer climate due to inland expansion of the area of the ice sheet bed which is
subject to inputs of meltwater from the ice sheet surface. The relationship between
surface melting and ice velocity is mediated, however, by the structure of the subglacial
drainage system and variations in the rate of meltwater drainage to the ice bed interface.
Insights from this work can help in the development of numerical ice sheet models which
aim to predict the future contribution to sea-level rise from the Greenland Ice Sheet
Disentangling within-person changes and individual differences among fundamental need satisfaction, attainment of acquisitive desires, and psychological health
We explored within-person and individual difference associations among basic psychological need satisfaction (autonomy, competence, and relatedness), attainment of acquisitive desires (wealth and popularity) and indicators of well- and ill-being. Participants were 198 undergraduates (51% male) who completed an inventory multiple times over a university semester. Analyses revealed that increased satisfaction of all the needs and desires beyond participants’ normal levels, with the exception of relatedness, were associated with greater psychological welfare. Nonetheless, individual differences in well-being were only predicted by psychological need satisfaction, and not by the attainment of acquisitive desires. Hence, the realization of acquisitive desires may elicit within-person increases in psychological welfare; however, satisfying innate needs may be a better bet for long term psychological health
Short-term variability in Greenland Ice Sheet motion forced by time-varying meltwater inputs: implications for the relationship between subglacial drainage system behavior and ice velocity.
High resolution measurements of ice motion along a -120 km transect in a land-terminating section of the GrIS reveal short-term velocity variations (<1 day), which are forced by rapid variations in meltwater input to the subglacial drainage system from the ice sheet surface. The seasonal changes in ice velocity at low elevations (<1000 m) are dominated by events lasting from 1 day to 1 week, although daily cycles are largely absent at higher elevations, reflecting different patterns of meltwater input. Using a simple model of subglacial conduit behavior we show that the seasonal record of ice velocity can be understood in terms of a time-varying water input to a channelized subglacial drainage system. Our investigation substantiates arguments that variability in the duration and rate, rather than absolute volume, of meltwater delivery to the subglacial drainage system are important controls on seasonal patterns of subglacial water pressure, and therefore ice velocity. We suggest that interpretations of hydro-dynamic behavior in land-terminating sections of the GrIS margin which rely on steady state drainage theories are unsuitable for making predictions about the effect of increased summer ablation on future rates of ice motion. © 2012. American Geophysical Union
Supraglacial forcing of subglacial drainage in the ablation zone of the Greenland ice sheet
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Variability in ice motion at a land-terminating Greenlandic outlet glacier: the role of channelized and distributed drainage systems
We use a combination of field observations and hydrological modelling to examine the mechanisms through which variability in meltwater input affects ice motion at a land-terminating Greenlandic outlet glacier. We find a close agreement between horizontal ice velocity, vertical ice velocity and modelled subglacial water pressure over the course of a melt season. On this basis, we argue that variation in horizontal and vertical ice velocity primarily reflects the displacement of basal ice during periods of cavity expansion and contraction, a process itself driven by fluctuations in basal water pressure originating in subglacial channels. This process is not captured by traditional sliding laws linking water pressure and basal velocity, which may hinder the simulation of realistic diurnal to seasonal variability in ice velocity in coupled models of glacial hydrology and dynamics
A conversation between Charles Spearman, Godfrey Thomson, and Edward L. Thorndike: The International Examinations Inquiry Meetings 1931-1938 (vol 11, pg 122, 2008)
Embedding the new science of research: the organised culture of Scottish educational research in the mid‐twentieth century
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The Research Software Encyclopedia is a community driven, open source strategy to define the term “research software” in different contexts. It consists of several elements: a base library to manage a database of software, criteria and taxonomy items that can be used to answer questions about the software in the database, and several ways for an interested party to interact. A community database is stored in version control (GitHub), and by way of providing and updating this database, the Research Software Encyclopedia takes a strategy of small contributions over time to grow a valuable resource. Using a community-driven open source approach offers a number of advantages over attempting to derive a single, holistic definition for research software. First, it takes into account the context under which the definition is considered. Second, community and scoped contributions to specific components of the task are easy. Third, it provides a resource that can be extended to other use cases. Finally, this initiative creates a solution that requires no grants or other funding to maintain, increasing its ability to grow, adapt, and evolve over time
“Intelligence and Civilisation”: A Ludwig Mond lecture delivered at the University of Manchester on 23rd October 1936 by Godfrey H. Thomson. A reprinting with background and commentary
Winter motion mediates dynamic response of the Greenland Ice Sheet to warmer summers
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