Antarctic supraglacial lakes (SGLs) have been linked to ice shelf collapse and the subsequent acceleration of inland ice flow, but observations of SGLs remain relatively scarce and their interannual ...variability is largely unknown. This makes it difficult to assess whether some ice shelves are close to thresholds of stability under climate warming. Here, we present the first observations of SGLs across the entire East Antarctic Ice Sheet over multiple melt seasons (2014-2020). Interannual variability in SGL volume is >200% on some ice shelves, but patterns are highly asynchronous. More extensive, deeper SGLs correlate with higher summer (December-January-February) air temperatures, but comparisons with modelled melt and runoff are complex. However, we find that modelled January melt and the ratio of November firn air content to summer melt are important predictors of SGL volume on some potentially vulnerable ice shelves, suggesting large increases in SGLs should be expected under future atmospheric warming.
Glacial lake outburst floods (GLOFs) represent a major hazard and can result in significant loss of life. Globally, since 1990, the number and size of glacial lakes has grown rapidly along with ...downstream population, while socio-economic vulnerability has decreased. Nevertheless, contemporary exposure and vulnerability to GLOFs at the global scale has never been quantified. Here we show that 15 million people globally are exposed to impacts from potential GLOFs. Populations in High Mountains Asia (HMA) are the most exposed and on average live closest to glacial lakes with ~1 million people living within 10 km of a glacial lake. More than half of the globally exposed population are found in just four countries: India, Pakistan, Peru, and China. While HMA has the highest potential for GLOF impacts, we highlight the Andes as a region of concern, with similar potential for GLOF impacts to HMA but comparatively few published research studies.
The Greenland Ice Sheet (GrIS) is losing mass in response to
recent climatic and oceanic warming. Since the mid-1990s, tidewater outlet
glaciers across the ice sheet have thinned, retreated, and ...accelerated, but
recent changes in northern Greenland have been comparatively understudied.
Consequently, the dynamic response (i.e. changes in surface elevation and
velocity) of these outlet glaciers to changes at their termini, particularly
calving from floating ice tongues, is poorly constrained. Here we use
satellite imagery and historical maps to produce an unprecedented 68-year
record of terminus change across 18 major outlet glaciers and combine this
with previously published surface elevation and velocity datasets. Overall,
recent (1995–2015) retreat rates were higher than at any time in the
previous 47 years (since 1948). Despite increased retreat rates from the
1990s, there was distinct variability in dynamic glacier behaviour depending
on whether the terminus was grounded or floating. Grounded glaciers
accelerated and thinned in response to retreat over the last 2 decades,
while most glaciers terminating in ice tongues appeared dynamically
insensitive to recent ice tongue retreat and/or total collapse. We also
identify glacier geometry (e.g. fjord width, basal topography, and ice tongue
confinement) as an important influence on the dynamic adjustment of glaciers
to changes at their termini. Recent grounded outlet glacier retreat and ice
tongue loss across northern Greenland suggest that the region is undergoing
rapid change and could soon contribute substantially to sea level rise via
the loss of grounded ice.
Accelerated discharge through marine-terminating outlet glaciers has been a key component of the rapid mass loss from Arctic glaciers since the 1990s. However, glacier retreat and its climatic ...controls have not been assessed at the pan-Arctic scale. Consequently, the spatial and temporal variability in the magnitude of retreat, and the possible drivers are uncertain. Here we use remotely sensed data acquired over 273 outlet glaciers, located across the entire Atlantic Arctic (i.e. areas potentially influenced by North Atlantic climate and/or ocean conditions, specifically: Greenland, Novaya Zemlya, Franz Josef Land and Svalbard), to demonstrate high-magnitude, accelerating and near-ubiquitous retreat between 1992 and 2010. Overall, mean retreat rates increased by a factor of 3.5 between 1992 and 2000 (−30.5 m a−1) and 2000–10 (−105.8 m a−1), with 97% of the study glaciers retreating during the latter period. The Retreat was greatest in northern, western and south-eastern Greenland and also increased substantially on the Barents Sea coast of Novaya Zemlya. Glacier retreat showed no significant or consistent relationship with summer air temperatures at decadal timescales. The rate of frontal position change showed a significant, but weak, correlation with changes in sea-ice concentrations. We highlight large variations in retreat rates within regions and suggest that fjord topography plays an important role. We conclude that marine-terminating Arctic outlet glaciers show a common response of rapid and accelerating retreat at decadal timescales.
Supraglacial lakes (SGLs) are now known to be widespread in Antarctica, where they represent an important component of ice sheet mass balance. This paper reviews how recent progress in satellite ...remote sensing has substantially advanced our understanding of SGLs in Antarctica, including their characteristics, geographic distribution and impacts on ice sheet dynamics. Important advances include: (a) the capability to resolve lakes at sub-metre resolution at weekly timescales; (b) the measurement of lake depth and volume changes at seasonal timescales, including sporadic observations of lake drainage events and (c) the integration of multiple optical satellite datasets to obtain continent-wide observations of lake distributions. Despite recent progress, however, there remain important gaps in our understanding, most notably: (a) the relationship between seasonal variability in SGL development and near-surface climate; (b) the prevalence and impact of SGL drainage events on both grounded and floating ice and (c) the sensitivity of individual ice shelves to lake-induced hydrofracture. Given that surface melting and SGL development is predicted to play an increasingly important role in the surface mass balance of Antarctica, bridging these gaps will help constrain predictions of future rapid ice loss from Antarctica.
Using a combination of Landsat, Pléiades and CORONA satellite imagery from 1967 to 2017, we map changes in the terminus position, ice surface velocity and surface elevation of Sabche Glacier, and ...report the first observations of surging behaviour in central Nepal. Our observations show that Sabche Glacier surged four times over the last 50 years. The three most recent surges occurred at 10 to 11-year cycles, which is one of the shortest surge cycles ever recorded. Detailed analysis of the most recent surge (2012 onwards), indicates that the glacier advanced 2.2 km and experienced maximum velocities of 1.6 ± 0.10 m day−1. During this surge, there was a surface elevation gain at the terminus of up to 90 ± 6.19 m a−1, with a corresponding surface lowering of between 10 ± 6.19 and 60 ± 6.19 m a−1, 3 km up-glacier of the terminus. This transfer of mass amounted to a volume of ~2.7 × 107 ± 0.1 × 107 m3a−1. Sabche Glacier is the first surge-type glacier to be observed in the central Himalayas, but this is consistent with a previous global analysis which indicates that surge-type glaciers should exist in the region. We hypothesise that the surge is at least partially controlled by subglacial topography, whereby a major subglacial overdeepening and constriction 3 km up-glacier of the terminus provides resistance to glacier flow from the accumulation area to the ablation area. This overdeepening appears to store mass until a threshold is crossed, after which the glacier flows out of the subglacial depression and rapidly surges over a bedrock lip and down the valley. Thus, whilst the surges are likely to be facilitated by subglacial processes (e.g. changes in subglacial hydrology and/or basal thermal regime), the topographic setting of the glacier appears to be modulating both the timing and duration of each surge.
•A new surge-type glacier in Nepal is identified using remote sensing techniques.•Sabche Glacier surged four times between 1967 and 2017.•The glacier has one of the shortest surge-cycles ever recorded.•The glacier shifted ~2.7 × 107 m3 of ice down-glacier during the most recent surge.•We suggest the surge is partly controlled by topography.
Supraglacial lakes (SGLs) enhance surface melting and can flex and
fracture ice shelves when they grow and subsequently drain, potentially
leading to ice shelf disintegration. However, the seasonal ...evolution of SGLs
and their influence on ice shelf stability in East Antarctica remains poorly
understood, despite some potentially vulnerable ice shelves having high
densities of SGLs. Using optical satellite imagery, air temperature data
from climate reanalysis products and surface melt predicted by a regional
climate model, we present the first long-term record (2000–2020) of seasonal
SGL evolution on Shackleton Ice Shelf, which is Antarctica's northernmost
remaining ice shelf and buttresses Denman Glacier, a major outlet of the
East Antarctic Ice Sheet. In a typical melt season, we find hundreds of SGLs
with a mean area of 0.02 km2, a mean depth of 0.96 m and a mean total
meltwater volume of 7.45×106 m3. At their most extensive, SGLs
cover a cumulative area of 50.7 km2 and are clustered near to the
grounding line, where densities approach 0.27 km2 km−2. Here,
SGL development is linked to an albedo-lowering feedback associated with
katabatic winds, together with the presence of blue ice and exposed rock.
Although below-average seasonal (December–January–February, DJF)
temperatures are associated with below-average peaks in total SGL area and
volume, warmer seasonal temperatures do not necessarily result in higher SGL
areas and volumes. Rather, peaks in total SGL area and volume show a much
closer correspondence with short-lived high-magnitude snowmelt events. We
therefore suggest seasonal lake evolution on this ice shelf is instead more
sensitive to snowmelt intensity associated with katabatic-wind-driven
melting. Our analysis provides important constraints on the boundary
conditions of supraglacial hydrology models and numerical simulations of ice
shelf stability.
The weakening and/or removal of floating ice shelves in Antarctica can induce inland ice flow acceleration. Numerical modelling suggests these processes will play an important role in Antarctica's ...future sea-level contribution, but our understanding of the mechanisms that lead to ice tongue/shelf collapse is incomplete and largely based on observations from the Antarctic Peninsula and West Antarctica. Here, we use remote sensing of structural glaciology and ice velocity from 2001 to 2020 and analyse potential ocean-climate forcings to identify mechanisms that triggered the rapid disintegration of ~2445 km2 of ice mélange and part of the Voyeykov Ice Shelf in Wilkes Land, East Antarctica between 27 March and 28 May 2007. Results show disaggregation was pre-conditioned by weakening of the ice tongue's structural integrity and was triggered by mélange removal driven by a regional atmospheric circulation anomaly and a less extensive latent-heat polynya. Disaggregation did not induce inland ice flow acceleration, but our observations highlight an important mechanism through which floating termini can be removed, whereby the break-out of mélange and multiyear landfast sea ice triggers disaggregation of a structurally-weak ice shelf. These observations highlight the need for numerical ice-sheet models to account for interactions between sea-ice, mélange and ice shelves.
The increasingly negative mass balance of the Greenland ice sheet (GrIS) over the last ~25 years has been associated with enhanced surface melt and increased ice loss from marine-terminating outlet ...glaciers. Accelerated retreat during 2000–2010 was concentrated in the southeast and northwest sectors of the ice sheet; however, there was considerable spatial and temporal variability in the timing and magnitude of retreat both within and between these regions. This behaviour has yet to be quantified and compared for all glaciers in both regions. Furthermore, it is unclear whether retreat has continued after 2010 in the northwest, and whether the documented slowdown in the southeast post-2005 has been sustained. Here, we compare spatial and temporal patterns of frontal change in the northwest and southeast GrIS, for the period 2000–2015. Our results show near-ubiquitous retreat of outlet glaciers across both regions for the study period; however, the timing and magnitude of inter-annual frontal position change is largely asynchronous. We also find that since 2010, there is continued terminus retreat in the northwest, which contrasts with considerable inter-annual variability in the southeast. Analysis of the role of glacier-specific factors demonstrates that fjord and bed geometry are important controls on the timing and magnitude of glacier retreat.
C-peptide declines in type 1 diabetes although many long-duration patients retain low, but detectable levels. Histological analyses confirm that beta cells can remain following type 1 diabetes onset. ...We explored the trends observed in C-peptide decline in UK Genetic Resource Investigating Diabetes (UK GRID) cohort (N=4,079), with beta cell loss in pancreas donors from the network for Pancreatic Organ donors with Diabetes (nPOD) biobank and the Exeter Archival Diabetes Biobank (EADB) (combined N=235), stratified by recently reported age at diagnosis endotypes (< 7, 7-12, ≥ 13 years) across increasing diabetes durations. The proportion of individuals with detectable C-peptide declined beyond the first year after diagnosis, but this was most marked in the youngest age group (< 1 year duration: age < 7 years: 18/20 (90%), 7-12 years: 107/110 (97%), ≥ 13 years: 58/61 (95%) versus. 1-5 years post diagnosis: < 7 years: 172/522 (33%), 7-12 years: 604/995 (61%), ≥ 13 years: 225/289 (78%)). A similar profile was observed in beta cell loss, with those diagnosed at younger ages experiencing more rapid loss of islets containing insulin-positive (insulin+) beta cells < 1 year post diagnosis: age < 7 years: 23/26 (88%), 7-12 years: 32/33 (97%), ≥ 13 years: 22/25 (88%) versus. 1-5 years post diagnosis: < 7 years: 1/12 (8.3%) ,7-12 years: 7/13 (54%), ≥ 13 years: 7/8 (88%)). These data should be considered in the planning and interpretation of intervention trials designed to promote beta cell retention and function.
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