Evaluation of existing and new methods of tracking glacier terminus change

ACKNOWLEDGEMENTS The authors thank two anonymous reviewers for constructive comments that helped to improve the manuscript. This research was financially supported by J.M.L.’s PhD funding from UK Natural Environment Research Council grant No. NE/I528742/1.Peer reviewedPublisher PD

Greenland: Bringing together remote sensing and fieldwork.

With global land and sea temperatures rising, the importance of accurate monitoring of the world's ice sheets is increasing. Satellite radar altimetry can be used to measure elevation changes of ice sheets from which mass balance can be derived. In the percolation zone of ice sheets, summer melt which percolates into the snowpack and refreezes causes a re-distribution of mass through densification, which can result in elevation changes which are not representative of changes in mass balance. We present data collected in the percolation zone of the Greenland Ice Sheet prior to and post the processes of summer melt, percolation and refreezing. Data from nine sites along two 1-km transects show that in 2004 there was a 31.6% increase in accumulation over the summer, but due to surface melting percolation and refreezing the average snowpack density increased by 26.2%, resulting in only a 5.3% increase in elevation. Our results indicate that in areas of substantial seasonal melt and refreezing, densification rates must be accurately quantified if mass balance estimates are to be usefully derived from surface elevation change

"The Economic Consequences of Weintraub's Consumption Coefficient"

In this paper we show that Weintraub:s consumption coefficient (the ratio of total consumption to wages) can elucidate trends in the sectoral and functional distributions of income We also show that, in a Kaleckian model, it simplifies and add precision to Kaleckian macroeconomics. Using a Kaleckian definition of profits, empirical estimates of the coefficient are presented for the UK 1972-1990. From a level of around 1.1 in the 1970’s, the coefficient rose to around 1.3 in the mid-1980s from which it has started to fall back to its 1970's levels. During the 1980s, the coefficient indicated a marked redistribution of income in favour of profits along with a rise in capitalists' propensity to consume. This confirms the evidence that the economic boom of the 1980s was driven principally by an expansion of demand for luxury goods rather than fixed capital investment. This will have been a factor in the slump after 1990.

The determinants of new orders of non-defence capital goods and its relationship to business fixed investment expenditures : 1992 to 2010

The determinant of nonfarm nonfinancial corporation orders of nondefense capital goods (as generated by the Census Bureau) is modelled during the period of 1992 to 2010. Statistically significant relationship between investment orders and the cyclical variations in output, the interest rate spread, net cash flows, the net increase in financial liabilities, the net increase in financial assets, and the value of (nondefense) manufacturing shipments is found. During the period 1992 to 2001, the wage share is inversely related to new orders. New orders are used to explain, subject to a lag, nonfarm nonfinancial corporations fixed investment expenditures, as generated by the BEA. A statistically significant relationship is found between investment expenditures and new orders, subject to modifications by changes contemporaneous economic conditions (largely reflected in cyclical changes in output, and, to a lesser extent, changes in the interest rate spread).peer-reviewe

Field-calibrated model of melt, refreezing, and runoff for polar ice caps : Application to Devon Ice Cap

Acknowledgments R.M.M. was supported by the Scottish Alliance for Geoscience, Environment and Society (SAGES). The field data collection contributed to the validation of the European Space Agency Cryosat mission and was supported by the Natural Sciences and Engineering Research Council, Canada, the Meteorological Service of Canada (CRYSYS program), the Polar Continental Shelf Project (an agency of Natural Resources Canada), and by UK Natural Environment Research Council consortium grant NER/O/S/2003/00620. Support for D.O.B. was provided by the Canadian Circumpolar Institute and the Climate Change Geoscience Program, Earth Sciences Sector, Natural Resources Canada (ESS contribution 20130371). Thanks are also due to the Nunavut Research Institute and the communities of Resolute Bay and Grise Fjord for permission to conduct fieldwork on Devon Ice Cap. M.J. Sharp, A. Gardner, F. Cawkwell, R. Bingham, S. Williamson, L. Colgan, J. Davis, B. Danielson, J. Sekerka, L. Gray, and J. Zheng are thanked for logistical support and field assistance during the data collection. We thank Ruzica Dadic, two other anonymous reviewers, and the Editor, Bryn Hubbard, for their helpful comments on an earlier version of this paper and which resulted in significant improvements.Peer reviewedPublisher PD

Terminus-driven retreat of a major southwest Greenland tidewater glacier during the early 19th century : insights from glacier reconstructions and numerical modelling

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Spatially distributed runoff at the grounding line of a large Greenlandic tidewater glacier inferred from plume modelling

Understanding the drivers of recent change at Greenlandic tidewater glaciers is of great importance if we are to predict how these glaciers will respond to climatic warming. A poorly constrained component of tidewater glacier processes is the near-terminus subglacial hydrology. Here we present a novel method for constraining near-terminus subglacial hydrology with application to marine-terminating Kangiata Nunata Sermia in South-west Greenland. By simulating proglacial plume dynamics using buoyant plume theory and a general circulation model, we assess the critical subglacial discharge, if delivered through a single compact channel, required to generate a plume that reaches the fjord surface. We then compare catchment runoff to a time series of plume visibility acquired from a time-lapse camera. We identify extended periods throughout the 2009 melt season where catchment runoff significantly exceeds the discharge required for a plume to reach the fjord surface, yet we observe no plume. We attribute these observations to spatial spreading of runoff across the grounding line. Persistent distributed drainage near the terminus would lead to more spatially homogeneous submarine melting and may promote more rapid basal sliding during warmer summers, potentially providing a mechanism independent of ocean forcing for increases in atmospheric temperature to drive tidewater glacier acceleration

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

Supraglacial forcing of subglacial drainage in the ablation zone of the Greenland ice sheet

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