Search

The generation, transport, storage and drainage of meltwater play important roles in the Greenland Ice Sheet (GrIS) subglacial system. Active subglacial lakes, common features in Antarctica, have recently been detected beneath the GrIS and may impact ice sheet hydrology. Despite their potential importance, few repeat subglacial lake filling and drainage events have been identified in Greenland. Here we examine the surface elevation change of a collapse basin at the Flade Isblink ice cap, northeast Greenland, which formed due to sudden subglacial lake drainage in 2011. We estimate the subglacial lake volume evolution using multi-temporal ArcticDEM data and ICESat-2 altimetry data acquired between 2012 and 2021. Our long-term observations show that the subglacial lake was continuously filled by surface meltwater, with the basin surface rising by up to 55 m during 2012–2021, and we estimate 138.2 × 106 m3 of meltwater was transported into the subglacial lake between 2012 and 2017. A second rapid drainage event occurred in late August 2019, which induced an abrupt ice dynamic response. We find that the 2019 drainage released much less water than the 2011 event and conclude that multiple factors, such as the volume of water stored in the subglacial lake and bedrock relief, regulate the episodic filling and drainage of the lake. By comparing the surface meltwater production and the subglacial lake volume change, we find that only ∼ 64 % of the surface meltwater descended to the bed, suggesting potential processes such as meltwater refreezing and firn aquifer storage, which need to be further quantified.

We describe several new ice velocity maps produced by the Greenland Ice Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbræ and Køge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbræ began slowing substantially in 2017, with a midsummer peak that was even slower than some previous winter minima. Over the last decade, we identify two major slowdown events at Køge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in north-west and south-west Greenland to produce a record of speed-up since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speed-up. In addition, we computed trends in winter flow speed for much of the south-west margin of the ice sheet and find little in the way of statistically significant changes over the period covered by our data. Finally, although the consistency of the data is generally good over time and across sensors, our analysis indicates that substantial differences can arise in regions with high strain rates (e.g. shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results.

Mass loss of Greenland’s glaciers and ice caps (GICs) is a major contributor to contemporary sea-level rise. Here, the authors identify the year 1997 as a tipping point in GICs mass loss induced by a rapid deterioration of the refreezing capacity of inland snow, resulting in irreversible long-term mass loss.

This study presents a data set of daily, 1 km resolution Greenland ice sheet (GrIS) surface mass balance (SMB) covering the period 1958–2015. Applying corrections for elevation, bare ice albedo and accumulation bias, the high-resolution product is statistically downscaled from the native daily output of the polar regional climate model RACMO2.3 at 11 km. The data set includes all individual SMB components projected to a down-sampled version of the Greenland Ice Mapping Project (GIMP) digital elevation model and ice mask. The 1 km mask better resolves narrow ablation zones, valley glaciers, fjords and disconnected ice caps. Relative to the 11 km product, the more detailed representation of isolated glaciated areas leads to increased precipitation over the southeastern GrIS. In addition, the downscaled product shows a significant increase in runoff owing to better resolved low-lying marginal glaciated regions. The combined corrections for elevation and bare ice albedo markedly improve model agreement with a newly compiled data set of ablation measurements.

We present a new bed elevation dataset for Greenland derived from a combination of multiple airborne ice thickness surveys undertaken between the 1970s and 2012. Around 420 000 line kilometres of airborne data were used, with roughly 70% of this having been collected since the year 2000, when the last comprehensive compilation was undertaken. The airborne data were combined with satellite-derived elevations for non-glaciated terrain to produce a consistent bed digital elevation model (DEM) over the entire island including across the glaciated–ice free boundary. The DEM was extended to the continental margin with the aid of bathymetric data, primarily from a compilation for the Arctic. Ice thickness was determined where an ice shelf exists from a combination of surface elevation and radar soundings. The across-track spacing between flight lines warranted interpolation at 1 km postings for significant sectors of the ice sheet. Grids of ice surface elevation, error estimates for the DEM, ice thickness and data sampling density were also produced alongside a mask of land/ocean/grounded ice/floating ice. Errors in bed elevation range from a minimum of ±10 m to about ±300 m, as a function of distance from an observation and local topographic variability. A comparison with the compilation published in 2001 highlights the improvement in resolution afforded by the new datasets, particularly along the ice sheet margin, where ice velocity is highest and changes in ice dynamics most marked. We estimate that the volume of ice included in our land-ice mask would raise mean sea level by 7.36 m, excluding any solid earth effects that would take place during ice sheet decay.

Competing Interests: Conflict of interest The authors declare that they have no conflict of interest.

We describe several new ice velocity maps produced by the Greenland Ice Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbrae and Koge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbrae began slowing substantially in 2017, with a mid-summer peak that was even slower than some previous winter minimums. Over the last decade, we identify two major slowdown events at Koge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in northwest and southwest Greenland to produce a record of speedup since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speedup. In addition, we computed trends in winter flow speed for much of the southwest margin of the ice sheet and find little in the way of statistically significant change over the period covered by our data. Finally, although consistency of the data generally is good through time and across sensors, our analysis indicates substantial differences can arise in regions with high strain rates (e.g., shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results.

Greenland's bed topography is a primary control on ice flow, grounding line migration, calving dynamics, and subglacial drainage. Moreover, fjord bathymetry regulates the penetration of warm Atlantic water (AW) that rapidly melts and undercuts Greenland's marine-terminating glaciers. Here we present a new compilation of Greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach. A new 150 m horizontal resolution bed topography/bathymetric map of Greenland is constructed with seamless transitions at the ice/ocean interface, yielding major improvements over previous data sets, particularly in the marine-terminating sectors of northwest and southeast Greenland. Our map reveals that the total sea level potential of the Greenland ice sheet is 7.42 ± 0.05 m, which is 7 cm greater than previous estimates. Furthermore, it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which AW can access glaciers with marine-based basins, thereby highlighting sectors of Greenland that are most vulnerable to future oceanic forcing.

Melting of the Greenland ice sheet (GrIS) and its peripheral glaciers and ice caps (GICs) contributes about 43% to contemporary sea level rise. While patterns of GrIS mass loss are well studied, the spatial and temporal evolution of GICs mass loss and the acting processes have remained unclear. Here we use a novel, 1 km surface mass balance product, evaluated against in situ and remote sensing data, to identify 1997 (±5 years) as a tipping point for GICs mass balance. That year marks the onset of a rapid deterioration in the capacity of the GICs firn to refreeze meltwater. Consequently, GICs runoff increases 65% faster than meltwater production, tripling the post-1997 mass loss to 36±16 Gt -1 , or ∼14% of the Greenland total. In sharp contrast, the extensive inland firn of the GrIS retains most of its refreezing capacity for now, buffering 22% of the increased meltwater production. This underlines the very different response of the GICs and GrIS to atmospheric warming.

Objective: Guidelines on the clinical use of growth hormone therapy in adults were issued by the UK National Institute for Clinical Excellence (NICE) in August 2003. We conducted a retrospective clinical audit on the use of growth hormone (GH) in Scotland to evaluate the use of these guidelines and their impact on clinical practice. The audit had two phases. In phase I, the impact of NICE criteria on specialist endocrine practice in starting and continuing GH replacement was assessed. In phase II, the reasons why some adults in Scotland with growth hormone deficiency were not on replacement therapy were evaluated., Methods: A retrospective cross-sectional case note review was carried out of all adult patients being followed up for growth hormone deficiency during the study period (1 March 2005 to 31 March 2008). Phase I of the audit included 208 patients and phase II 108 patients., Results: Sellar tumours were the main cause of GH deficiency in both phases of the audit. In phase I, 53 patients (77%) had an AGHDA-QoL score >11 documented before commencing GH post-NICE guidance, compared with 35 (25%) pre-NICE guidance. Overall, only 39 patients (18%) met the full NICE criteria for starting and continuing GH (pre-NICE, 11%; post-NICE, 35%). Phase II indicated that the main reasons for not starting GH included perceived satisfactory quality of life (n = 47, 43%), patient reluctance (16, 15%) or a medical contraindication (16, 15%)., Conclusions: Although the use of quality of life assessments has increased following publication of the NICE guidelines, most adults on GH in Scotland did not fulfil the complete set of NICE criteria. The main reason for not starting GH therapy in adult GH-deficient patients was perceived satisfactory quality of life., (© 2012 Blackwell Publishing Ltd.)

Earlier observations on several of Greenland's outlet glaciers, starting near the turn of the 21st century, indicated rapid (annual-scale) and large (>100%) increases in glacier velocity. Combining data from several satellites, we produce a decade-long (2000 to 2010) record documenting the ongoing velocity evolution of nearly all (200+) of Greenland's major outlet glaciers, revealing complex spatial and temporal patterns. Changes on fast-flow marine-terminating glaciers contrast with steady velocities on ice-shelf-terminating glaciers and slow speeds on land-terminating glaciers. Regionally, glaciers in the northwest accelerated steadily, with more variability in the southeast and relatively steady flow elsewhere. Intraregional variability shows a complex response to regional and local forcing. Observed acceleration indicates that sea level rise from Greenland may fall well below proposed upper bounds.

Background: Patients with fractures should be prioritized for assessment for osteoporosis so that they can benefit from treatment for the secondary prevention of osteoporotic fractures. Assessment is seldom offered to patients with vertebral fractures because these fractures are typically not diagnosed. Vertebral fractures can be identified by vertebral fracture assessment (VFA) using current dual-energy X-ray absorptiometry (DXA) scanners., Objective: The purpose of this study was to assess the prevalence of vertebral fractures, using VFA, in patients presenting with nonvertebral fractures and to assess whether this impacts on the management of these patients., Design: A cohort study undertaken in 577 patients aged 50 years or over including 455 women, who presented with nonvertebral fractures and who underwent routine post-fracture assessment by a Fracture Liaison Service (FLS)., Measurements: The numbers and severity of vertebral fractures were assessed in evaluable vertebrae from TV4 to LV4 in addition to bone mineral density (BMD) assessment., Results: Using DXA, 76% of vertebrae could be evaluated by VFA. Of the men and women with nonvertebral fractures, 19-20% had at least one vertebral fracture. The prevalence ranged from 6% in men with humeral fractures to 32% among women with hip fractures. The prevalence of vertebral fractures correlated most strongly with increasing age and with severity of reduction of BMD. Using local treatment protocols, VFA would result in only 3% more patients receiving treatment for fracture secondary prevention., Conclusions: In patients with nonvertebral fractures, VFA identifies a substantial burden of prevalent vertebral fractures that have not hitherto been recognized. Nevertheless, VFA seldom influences the need for treatment for fracture secondary prevention after a nonvertebral fracture.