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Repeat airborne laser altimetry measurements show widespread thinning (surface lowering) of glaciers in Canada's Queen Elizabeth Islands since 1995. Thinning rates averaged for 50 m elevation bins, were more than three times higher during the period 2005/06 to 2012/14 pentad than during the previous two pentads. Strongly negative thickness change (dh/dt) anomalies from 2005/06 to 2012/14, relative to the 1995–2012/14 mean, suggest that most of the measured thinning occurred during the most recent 5–6 year period when mean summer land surface temperatures (LSTs) were anomalously high and the mean summer black-sky shortwave broadband albedos (BSA) were anomalously low, relative to the 2000/01–15/16 period, and upper-air (700 hPa) and near surface (2 m) air temperatures were between 0.8°C and 1.5°C higher than 1995–2012 mean. Comparisons of dh/dt with mean summer LST and BSA measurements from the Moderate Resolution Imaging Spectroradiometer and with surface longitudinal strain rates computed from surface velocity fields derived from RADARSAT 1/2 and Landat-7 ETM + data suggest that surface elevation changes were driven mainly by changes in climate. An exception to this occurs along many fast-flowing outlet glaciers where ice dynamics appear also to have played an important role in surface elevation changes.
Significant intra-annual variability in flow rates of tidewater-terminating Arctic glaciers has been observed in recent years. These changes may result from oceanic and/or atmospheric forcing through (1) perturbations at the terminus, such as enhanced submarine melt and changes in sea-ice buttressing, or (2) increased surface melt, in response to atmospheric warming, reaching the bed and promoting glacier slip. We examine the influence of these processes on Belcher Glacier, a large fast-flowing tidewater outlet of the Devon Island ice cap in the Canadian Arctic. A hydrologically-coupled higher-order ice flow model is used to estimate changes in glacier flow speed as a result of changes in sea-ice buttressing and hydrologically-driven melt-season dynamics. Daily run-off from five sub-catchments over the 2008 and 2009 melt seasons provides meltwater forcing for the model simulations. Model results are compared with remotely-sensed and in situ ice-surface velocity measurements. Sea-ice effects are found to have a minor influence on glacier flow speed relative to that of meltwater drainage, which is clearly implicated in short-term velocity variations during the melt season. We find that threshold drainage is essential in determining the timing of these short-lived accelerations.
Feature tracking of approximately annually separated Landsat-7 ETM+ imagery acquired from 1999 to 2010 and speckle tracking of 24-day separated RADARSAT-2 imagery acquired from 2009 to 2015 reveal that motion of the major tidewater glaciers of Devon Ice Cap is more variable than previously described. The flow of almost half (six of 14) of the outlet glaciers slowed over the observation period, while that of the terminus regions of three of 14 of the glaciers sped up in the most recent years of observation. The North Croker Bay Glacier of southern Devon Ice Cap showed the greatest variability in motion, oscillating between multi-year (three or more) periods of slower and faster flow and exhibited a pattern of velocity variability that is different from that of the rest of the ice cap's outlet glaciers. Comparisons between areas of dynamic variability and glacier bed topography indicate that velocity variability is largely restricted to regions where the glacier bed is grounded below sea level. Derived velocities are combined with measurements of ice thickness at the fronts of tidewater glacier to determine a mean annual (2009; 2011–15) dynamic ice discharge of 0.41 ± 0.11 Gt a−1 for Devon Ice Cap. The Belcher Glacier is becoming a larger source of mass loss via ice discharge.
Canada's Queen Elizabeth Islands (QEI) contain ~14% of the world's glacier and ice-cap area. Sparse in-situ measurements indicate that interannual variability in glacier surface mass balance in this region is driven primarily by variations in summer melt, and that the annual surface mass balance of four index glaciers has become increasingly negative since 2007. Here, we use a 16-a record of satellite-derived mean summer (June–August) land surface temperatures (LST) from NASA's Moderate Resolution Imaging Spectroradiometer to investigate large-scale spatial and temporal variability in the duration and intensity of summer melt across glaciated surfaces in the QEI from 2000 to 2015. During this period, QEI mean summer glacier surface temperatures increased at an average rate of 0.06 ± 0.04°C a−1, for a total of nearly 1°C. Most of this increase occurred between 2005 and 2012, when mean summer near-surface (2 m) and upper-air (700 hPa) temperatures were 1.0–1.2°C higher than the 1948–2015 mean. There is a strong correlation between the glacier LST and 700 hPa air temperature records (r> 0.8). The period 2005–12, when mean summer LSTs were anomalously high, was likely the warmest period in the region since at least 1948.
Cryoconite holes can be important sources and stores of water and nutrients on cold and polythermal glaciers, and they provide a habitat for various forms of biota. Understanding the hydrological connectivity of cryoconite holes may be the key to understanding the transport of nutrients and biological material to the proglacial areas of such glaciers. This paper aims to characterize and explain spatial variability in the connectivity of ice-lidded cryoconite holes on a small, piedmont glacier in the McMurdo Dry Valleys through geochemical analysis of cryoconite hole waters. Solute concentrations in both surface and near-surface ice and cryoconite holes, vary greatly along the glacier centerline, and all sample types displayed similar spatial patterns of variability. Using chloride as a tracer, we estimated variations in cryoconite hole connectivity along the glacier centerline. We found that a previously used mass transfer method did not provide reliable estimates of the time period for which cryoconite hole waters had been isolated from the atmosphere. We attribute this to spatial variability in both the chloride content of the surface ice and surface ablation rates. The approach may, however, be used to qualitatively characterize spatial variations in the hydrological connectivity of the cryoconite holes. These results also suggest that ice-lidded cryoconite holes are never truly isolated from the near-surface drainage system.
The subglacial chemical weathering environment is largely controlled by low temperatures and the presence of freshly comminuted minerals with a high surface area. These characteristics are believed to promote dissolution processes that give rise to low silica and high Ca2+ fluxes emanating from glacierized basins. We test an alternative hypothesis, that mineral precipitation reactions in the subglacial environment play an equally important role in controlling the water chemistry in glacierized basins. We analyze borehole and proglacial water chemistry from a subarctic polythermal glacier, complemented by mineral XRD analysis of suspended sediment, till and bedrock samples. In conjunction with a thermodynamic analysis of the water and mineral chemistry, we use reaction-path modelling to study the chemical enrichment of water through the glacier system. We find that the high pH of the subglacial environment is conducive to secondary mineral precipitation, and that it is not possible to balance the water chemistry using dissolution reactions alone. We show that low silica can be explained by standard weathering reactions without having to invoke mineral-leaching reactions. Our results suggest that subglacial weathering intensity may be significantly underestimated if the production of secondary minerals is not considered.
Supraglacial meltwater reaching a glacier bed can increase ice surface velocities via hydraulic jacking and enhanced basal sliding. However, the relationships between the structure of supraglacial drainage systems, sink-point distributions, glacier flow processes and the magnitude of interannual velocity variability are poorly understood. To explore the hypothesis that spatial variations in the rate and mechanisms of glacier flow are linked to variations in supraglacial drainage system structure and sink-point distribution across an ice cap, we mapped supraglacial drainage systems on Devon Ice Cap from Landsat-7 ETM+ imagery. Spatial patterns of surface velocity and interannual velocity variability were determined using gradient correlation applied to Landsat-7 ETM+ images. Velocity variability is greater in areas close to sink-point locations, presumably because hydrologically forced basal sliding and/or bed deformation are enhanced in such areas. The distribution and characteristics of supraglacial drainage systems may play an important role in determining the distribution of regions of basal sliding, highlighting the need for knowledge of the supraglacial drainage system structure and sink-point distribution to inform efforts to model the dynamic response of Arctic ice caps to future climate warming.
The Randolph Glacier Inventory (RGI) is a globally complete collection of digital outlines of glaciers, excluding the ice sheets, developed to meet the needs of the Fifth Assessment of the Intergovernmental Panel on Climate Change for estimates of past and future mass balance. The RGI was created with limited resources in a short period. Priority was given to completeness of coverage, but a limited, uniform set of attributes is attached to each of the ~198 000 glaciers in its latest version, 3.2. Satellite imagery from 1999–2010 provided most of the outlines. Their total extent is estimated as 726 800 ± 34 000 km2. The uncertainty, about ±5%, is derived from careful single-glacier and basin-scale uncertainty estimates and comparisons with inventories that were not sources for the RGI. The main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover. These errors appear not to be normally distributed, and quantifying them reliably is an unsolved problem. Combined with digital elevation models, the RGI glacier outlines yield hypsometries that can be combined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers. The RGI has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume, and thus actual and potential contributions to sea-level rise.
Evaluation of how accurately snowpack models can capture hydrological processes in firn is critical to determining how well they will simulate future glacier mass-balance changes. Here we compare simulations using the Crocus snowpack model with the evolving firn stratigraphy recorded in 14 cores drilled at four elevations in the accumulation zone of Devon Ice Cap, Canada, during the 2004–12 period of rapid summer warming. Simulations were forced with a combination of surface observations and reanalysis data. Simulations resulted in positive model bias in near-surface density, and negative bias in density at depth compared to observations. Results point to the importance of incorporating heterogeneous percolation in firn in order to improve the representation of meltwater flow, better reproduce observed firn density and temperature profile evolution, and improve simulations of glacier mass balance during periods of climate warming.
Co-morbid major depression occurs in approximately 10% of people suffering from a chronic medical condition such as cancer. Systematic integrated management that includes both identification and treatment has been advocated. However, we lack information on the cost-effectiveness of this combined approach, as published evaluations have focused solely on the systematic (collaborative care) treatment stage. We therefore aimed to use the best available evidence to estimate the cost-effectiveness of systematic integrated management (both identification and treatment) compared with usual practice, for patients attending specialist cancer clinics.
We conducted a cost-effectiveness analysis using a decision analytic model structured to reflect both the identification and treatment processes. Evidence was taken from reviews of relevant clinical trials and from observational studies, together with data from a large depression screening service. Sensitivity and scenario analyses were undertaken to determine the effects of variations in depression incidence rates, time horizons and patient characteristics.
Systematic integrated depression management generated more costs than usual practice, but also more quality-adjusted life years (QALYs). The incremental cost-effectiveness ratio (ICER) was £11 765 per QALY. This finding was robust to tests of uncertainty and variation in key model parameters.
Systematic integrated management of co-morbid major depression in cancer patients is likely to be cost-effective at widely accepted threshold values and may be a better way of generating QALYs for cancer patients than some existing medical and surgical treatments. It could usefully be applied to other chronic medical conditions.
Depression is a leading cause of disease burden worldwide and is especially problematic in people with chronic diseases, including cancer. Although depression can be effectively treated in the general population using antidepressant medication and psychological treatments, these treatments may have different benefits and harms in cancer patients. Previous reviews have not adequately addressed this topic. We therefore aimed to determine which, if any, treatments are effective for patients with diagnoses of both cancer and depression.
We conducted a systematic review of relevant randomized controlled trials identified through searches of Medline, EMBASE, PsycINFO and The Cochrane Central Register of Controlled Trials (CENTRAL).
Seven relatively small trials met the selection criteria. These provided some evidence that antidepressant medication, given alone or in combination with a psychological treatment, may be effective. We found no good evidence for psychological treatments given alone or for any other forms of treatment.
There is very limited evidence from clinical trials to guide the treatment of cancer patients with a diagnosis of depression, especially for psychological treatments. High quality trials of treatments for depression in patients with cancer are urgently needed.
Ground-penetrating radar (GPR) surveys at a center frequency of 500 MHz were used to determine winter (2007/08) and net annual (2005–07) snow water equivalent (SWE) patterns across the upper parts of Belcher Glacier, Devon Ice Cap, Nunavut, Canada. The GPR measurements were validated against snow depths determined from avalanche probe measurements, and converted to SWE values using densities measured with a down-borehole neutron density probe and in shallow snow pits. Distinct internal reflection horizons (IRHs) in the GPR record were formed during warm summers in 2007 and 2005, and a large rain event in summer 2006 which caused ice to accumulate above the 2005 melt surface. Elevation provides the dominant control on winter SWE distribution across the basin, with surface topography (e.g. gullies) also being locally important. Based on the location where IRHs intersected the ice-cap surface, the basin-wide firn line occurred at an altitude of 1260–1300 m over the period 2005–08. Net mass balance across the accumulation area of Belcher Glacier averaged 0.24 m w.e. a−1 over the period 2005–07, mainly dependent on altitude. This is a little higher than most previous estimates for the period since the 1960s, although the differences lie within error limits.
Marine-terminating glaciers may experience seasonal and short-term flow variations, which can impact rates of ice flux through the glacier terminus. We explore the relationship between variability in the flow of a large tidewater glacier (Belcher Glacier, Nunavut, Canada), the seasonal cycle of surface meltwater production and the rapid drainage of supraglacial lakes. We demonstrate a novel method for analyzing time-lapse photography to quantify lake area change rates (a proxy for net filling and drainage rates) and develop a typology of lake drainage styles. GPS records of ice motion reveal four flow acceleration events which can be linked to lake drainage events discovered in the time-lapse photography. These events are superimposed on a longer pattern of velocity variation that is linked to seasonal variation in surface melting. At the terminus of the glacier, the ice displacement associated with the lake drainage events constitutes ∼10% of the seasonally accelerated displacement or 0.4% of the total annual ice displacement (336 m a−1). While the immediate ice response to these individual perturbations may be small, these drainage events may enhance overall seasonal acceleration by opening and/or sustaining meltwater conduits to the glacier bed.
Using June–August surface meteorological measurements for 2004–10 we found that the duration of the summer melt season at elevations of 1800, 1300 and 1000 m a.s.l. on Devon Ice Cap, Canada, increased at a rate of 3.4 (p < 0.1; weak significance), 6.1 (p< 0.01) and 8.8 (p < 0.05) days a−1, respectively. The calculated surface melt rate at 1300m a.s.l. increased from 74 to 133 cm w.e. a−1 between 2007 and 2010. These changes are linked to two types of change in the Arctic atmospheric circulation. Strengthening of the 500 hPa ridge over the Arctic in June–July resulted in increases in both the advection of warm air into the region and the occurrence of cloud-free conditions over the ice cap, causing the available melt energy to increase by 4–24% relative to June–July 2007–10 mean conditions. More frequent southwesterly low-pressure systems in August after 2004 accounted for a 12–38% increase in available melt energy relative to the August 2007–10 daily mean due to advection of warm air into the Arctic, reduced incoming shortwave radiation and increased net longwave radiation. This delayed the timing of freeze-up by an average of 5.5 days a–1 (p < 0.05) at the three sites over 2004–10.
Estimating regional-scale rates of glacier mass change from repeat airborne and satellite altimetry requires assumptions about the density of the material being added to, or removed from, the glacier surface. This may vary in both space and time, especially in a period of warming climate such as has occurred in Arctic Canada since 2005. Here we compare firn properties measured on 20 shallow cores recovered from elevations of 1400–1900 m a.s.l. on Devon Ice Cap in 2012 with equivalent measurements from 34 cores recovered from the same locations between 2004 and 2011. The average density of the top 2.5 m of the firn column has increased by 13–80%. As a result, measured rates of density increase in the top 1.25 mw.e. of the firn layer have likely thinned this layer at rates of 0.021–0.168 m a−1 over the period 2004–12. These thinning rates are significant relative to local rates of surface height change measured by repeat airborne laser altimetry between 2004 and 2012 (−0.077 to −0.252 m a−1) and indicate that, during periods of climate warming or cooling, firn densification rate changes must be taken into account when estimating mass change rates from measured height changes.
Speckle tracking of repeat RADARSAT-2 fine-beam imagery acquired over 24 day periods in March 2009 allowed the creation of updated surface motion maps for the entire Devon Ice Cap, Canada. Error analysis indicates that speckle tracking can determine ice motion to an accuracy of ~5 ma-1. Comparisons with earlier velocity maps from the mid-1990s and 2000 reveal velocity patterns that largely agree with flow regimes described previously. However, motion determined along East5 Glacier indicates an increase in surface velocities between the studies. Additionally, Southeast2 Glacier has significantly accelerated over the past decade, with velocities greater in 2009 than in the early 1990s along almost the entire length of the glacier. This is likely indicative of a surge. Present-day total mass loss from Devon Ice Cap due to iceberg calving is calculated as 0.40 ± 0.09 Gta-1, similar to that reported by Burgess and others (2005), with Belcher Glacier accounting for ~42% of the entire loss.
This study investigates the impact of sea-ice conditions on the production of iceberg plumes from two tidewater glaciers on Devon Ice Cap, Nunavut, Canada. These effects are quantified using a 12 year RADARSAT-1 satellite record from 1997–2008 that contains imagery from approximately every 1–2 weeks in the winter and every 1–4 days in the summer. Iceberg plumes identified in this record are verified against terrestrial time-lapse photography of Belcher Glacier from 2007–08. Results suggest a strong relationship between iceberg plumes and the retreat of sea ice from the glacier termini, with the plumes caused by both the release of previously calved icebergs (ice melange) and new glacier calving. Iceberg plumes are also sometimes observed at other times in the summer and in midwinter (occasionally on both glaciers simultaneously), with these events likely due to new glacier calving alone. Analysis of tides and air temperatures suggests that they provide a minor influence on the timing of iceberg plumes. Instead, it appears that changes in the presence of sea ice are dominant on seasonal timescales, although internal glacier dynamics likely play a significant role for winter plume events that occur when substantial thicknesses of landfast sea ice are present.
We have successfully developed a Seebeck coefficient Standard Reference Material (SRM™), Bi2Te3, that is essential for interlaboratory data comparison and for instrument calibration. Certification measurements were performed using a differential steady-state technique on 10 samples (15 measurements) randomly selected from a batch of 390 bars. The certified Seebeck coefficient values are provided from 10 to 390 K, and they are further supported by transient measurements. The availability of this SRM will validate measurement results, leading to a better understanding of the structure/property relationships and underlying physics of potential high-efficiency thermoelectric materials.