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.
Since the discovery of thick ice deposits on the polar caps of Mars, scientists have proposed that they flow as glaciers or ice sheets, and simultaneously, others have suggested that erosional ...activity, primarily by wind, has been the main driver shaping them. This debate began in 1971, and following those original interpretations, numerous studies have suggested that the PLDs flow, up to 1 m per year at steep marginal scarps, and numerous subsequent studies have negated those interpretations. Further, each time a testable prediction has been made in support of flow, is has been falsified by observations. To date, no flow has been observed at the PLDs. This creates an enduring problem; according to conventional wisdom, the polar caps “should” be flowing, but they have not in any appreciable, measurable way. Here, I review the evidence for and against flow and offer and test four hypotheses to retard flow of the NPLD based. The first three hypotheses overpredict strain and fail to account for other observations. The fourth hypothesis, based on stratified layers of varying rheology, successfully explains why the polar ice has no measurable flow.
The polar ice caps of Mars together comprise as much ice as the Greenland Ice Sheet on Earth. They reach 2–3 km thick and span >1000 km. On Earth, where ice is as many as 100° warmer, places with ice ∼1 km thick flow at a measurable rate. However, at the poles of Mars, all predictions of a flowing ice sheet have been negated by observations – any flow would have to be so miniscule as to have no effect on the surface or be detectable in the stratigraphy. Mars does have abundant evidence of past flowing ice in the mid-latitudes, mostly as glaciers, and the poles have experienced temperatures warm enough for flow in the recent past, so explaining this lack of evidence for flow has eluded scientists. This manuscript proposes four ideas to inhibit flow and finds one based on stacking layers of alternating viscosity to successfully match observations. The more resistant layers act to reduce overall flow to an undetectable level.
•The polar ice on Mars “should” flow; however, all past interpretations of flowing polar ice on Mars have been invalidated•I provide and test four hypotheses to explain the lack of observations supporting flow over 50+ years•Stratified materials that impede bulk flow explains the observations better than all past interpretations or models
Glaciers, gender, and science Carey, Mark; Jackson, M.; Antonello, Alessandro ...
Progress in human geography,
12/2016, Letnik:
40, Številka:
6
Journal Article
Recenzirano
Glaciers are key icons of climate change and global environmental change. However, the relationships among gender, science, and glaciers – particularly related to epistemological questions about the ...production of glaciological knowledge – remain understudied. This paper thus proposes a feminist glaciology framework with four key components: 1) knowledge producers; (2) gendered science and knowledge; (3) systems of scientific domination; and (4) alternative representations of glaciers. Merging feminist postcolonial science studies and feminist political ecology, the feminist glaciology framework generates robust analysis of gender, power, and epistemologies in dynamic social-ecological systems, thereby leading to more just and equitable science and human-ice interactions.
We examine the evolution of sea-ice extent (SIE) over both polar regions for 35 years from November 1978 to December 2013, as well as for the global total ice (Arctic plus Antarctic). Our examination ...confirms the ongoing loss of Arctic sea ice, and we find significant (p˂ 0.001) negative trends in all months, seasons and in the annual mean. The greatest rate of decrease occurs in September, and corresponds to a loss of 3 x 106 km2 over 35 years. The Antarctic shows positive trends in all seasons and for the annual mean (p˂0.01), with summer attaining a reduced significance (p˂0.10). Based on our longer record (which includes the remarkable year 2013) the positive Antarctic ice trends can no longer be considered ‘small’, and the positive trend in the annual mean of (15.29 ± 3.85) x 103 km2 a–1 is almost one-third of the magnitude of the Arctic annual mean decrease. The global annual mean SIE series exhibits a trend of (–35.29 ± 5.75) x 103 km2 a-1 (p<0.01). Finally we offer some thoughts as to why the SIE trends in the Coupled Model Intercomparison Phase 5 (CMIP5) simulations differ from the observed Antarctic increases.
World Scientists’ Warning to Humanity RIPPLE, WILLIAM J.; WOLF, CHRISTOPHER; NEWSOME, THOMAS M. ...
Bioscience,
12/2017, Letnik:
67, Številka:
12
Journal Article
Abstract
One of the largest contributors to uncertainty in predictions of sea-level rise from ice-sheet models is a lack of knowledge about the bed topography beneath ice sheets. Bed topography maps ...are normally made by interpolating between linear radar surveys using methods that include kriging, mass conservation and flowline diffusion, all of which may miss influential mesoscale (2–30 km) bedforms. Previous works have explored an Ice-Flow Perturbation Analysis (IFPA) approach for estimating bed topography using the surface expression of these mesoscale bedforms. Using regions of Pine Island Glacier that have been intensively surveyed by ice-penetrating radar as test sites, and a refined IFPA methodology, we find that IFPA detects bedforms capable of influencing ice flow which are not represented in Bedmachine Antarctica and other interpolated bed products. We further explore the ability of IFPA to estimate relative bed slipperiness, finding higher slipperiness in the main trunk and tributaries. Alongside other methods which estimate ice thickness, bed topography maps from IFPA have the potential to constrain projections of future sea-level rise, especially where radar data are sparse.
Abstract
Although over 600 Antarctic subglacial lakes have been identified using radar and satellite observations, the bathymetry and bed properties, which are key to understanding conditions within ...the lake, have been determined in very few localities. We present measurements of water column thickness and lakebed properties from Lago Subglacial CECs (SLC), located beneath 2653 m of ice at the Rutford-Institute-Minnesota divide in Antarctica. Seismic profiles indicate a maximum water column thickness of 301.3 ± 1.5 m, at the widest part of the lake, with an estimated lake volume of 2.5 ± 0.3 km
3
. Seismic imaging and measurements of the reflection strength at the ice base and lakebed indicate >15 m of high-porosity fine-grained sediment in the central section of the lakebed, consistent with a depositional sequence with an age of up to 0.5 Ma. These observations, along with previous radar measurements and modelling, indicate a low-energy sedimentary environment with a long water-residence time. As such, SLC is a suitable target for exploration via direct access to recover sediment records of ice sheet and climate history and investigate microbial life with long periods of isolation.
Glacier seismology is a valuable tool for investigating ice flow dynamics, but sufficient data acquisition in remote and exposed glaciated terrain remains challenging. For data acquisition on a ...highly crevassed and remote outlet glacier in Greenland we developed self-sufficient and easily deployable seismic stations, "SG-boxes". The SG-boxes contain their own power supply via solar panel, a three-component omni-directional geophone and a GNSS receiver. The SG-boxes can be deployed and retrieved from a hovering helicopter, allowing for deployment in difficult terrain. To assess their performance we conducted a field test comparing the SG-boxes to established on-ice geophone installations at Gornergletscher in Switzerland. Moreover, data from a first SG-box deployment in Greenland were analyzed. The SG-boxes exhibit consistently higher noise levels relative to colocated conventional geophones and a correlation between noise levels, wind and air temperature is found. Despite their noise susceptibility, the SG-boxes detected a total of 13,114 Gornergletscher icequakes over 10 days, which is 30% of the total number of icequakes detected by conventional geophone stations. Hence, even in sub-optimal weather conditions and without additional noise reduction measures, the SG-boxes can provide unique and valuable data from challenging glaciated terrain where no conventional seismic installations are possible.
Seafloor methane release due to the thermal dissociation of gas hydrates is pervasive across the continental margins of the Arctic Ocean. Furthermore, there is increasing awareness that shallow ...hydrate-related methane seeps have appeared due to enhanced warming of Arctic Ocean bottom water during the last century. Although it has been argued that a gas hydrate gun could trigger abrupt climate change, the processes and rates of subsurface/atmospheric natural gas exchange remain uncertain. Here we investigate the dynamics between gas hydrate stability and environmental changes from the height of the last glaciation through to the present day. Using geophysical observations from offshore Svalbard to constrain a coupled ice sheet/gas hydrate model, we identify distinct phases of subglacial methane sequestration and subsequent release on ice sheet retreat that led to the formation of a suite of seafloor domes. Reconstructing the evolution of this dome field, we find that incursions of warm Atlantic bottom water forced rapid gas hydrate dissociation and enhanced methane emissions during the penultimate Heinrich event, the Bølling and Allerød interstadials, and the Holocene optimum. Our results highlight the complex interplay between the cryosphere, geosphere, and atmosphere over the last 30,000 y that led to extensive changes in subseafloor carbon storage that forced distinct episodes of methane release due to natural climate variability well before recent anthropogenic warming.
Abstract
The current paper studies the dynamics and age of the Triangle du Tacul (TDT) ice apron, a massive ice volume lying on a steep high-mountain rock wall in the French side of the Mont-Blanc ...massif at an altitude close to 3640 m a.s.l. Three 60 cm long ice cores were drilled to bedrock (i.e. the rock wall) in 2018 and 2019 at the TDT ice apron. Texture (microstructure and lattice-preferred orientation, LPO) analyses were performed on one core. The two remaining cores were used for radiocarbon dating of the particulate organic carbon fraction (three samples in total). Microstructure and LPO do not substantially vary with along the axis of the ice core. Throughout the core, irregularly shaped grains, associated with strain-induced grain boundary migration and strong single maximum LPO, were observed. Measurements indicate that at the TDT ice deforms under a low strain-rate simple shear regime, with a shear plane parallel to the surface slope of the ice apron. Dynamic recrystallization stands out as the major mechanism for grain growth. Micro-radiocarbon dating indicates that the TDT ice becomes older with depth perpendicular to the ice surface. We observed ice ages older than 600 year BP and at the base of the lowest 30 cm older than 3000 years.
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