Central Glacier Research Articles

Elevation changes (1949–1995) of Black Rapids Glacier, Alaska, derived from a multi-baseline InSAR DEM and historical maps

AbstractWe have constructed a new digital elevation model (DEM) of the 1995 surface of Black Rapids Glacier, a surge-type glacier in the central Alaska Range, using ERS-1/-2 repeat-pass interferometry. We isolated the topographic phase from three interferograms with contrasting perpendicular baselines. Numerous phase-unwrapping errors caused by areas of poor coherence were corrected in all three interferograms, using a novel, iterative, semi-automated approach that capitalizes on the multi-baseline nature of the dataset. Comparison of our DEM with a 1949 US Geological Survey DEM and with 1973–95 ground survey data shows the gradual return of Black Rapids Glacier to a pre-surge hypsometry following a surge in 1936/37. Maximum elevation changes along the glacier center line in the ablation and accumulation areas are, respectively, −249 and +63 m (−5.4 and +1.4 m a−1). Maximum elevation changes of survey points at nearby locations are −4.9 m a−1 (1975–84) and +0.5 m a−1 (1975–85). Center-line thickening of +62 m between 1949 and 1995 (+1.4 m a−1), just above the Loket tributary in the upper part of the ablation zone, indicates dynamic thickening following the 1936/37 surge.

Comparing Surface Height Used in NCAR Climate Model with That Observed by ICEsat: Effects on Skin Temperature Simulation

This paper tries to identify one of the reasons for the poor land skin temperature simulated by a climate model over Greenland. It first compares ICEsat surface height measurements over Greenland with those used by the model and reveals that the surface height of Greenland prescribed in the National Center for Atmospheric Research (NCAR) Community Climate System Model/Community Land Model version 3 (CCSM/CLM3) differs greatly from the satellite measurements from National Aeronautics and Space Administration (NASA) ICEsat at edges and central glacier regions. This deficiency, in part, leads to underestimated skin temperatures at coastal regions—the areas where significant ice sheet melt is observed. Furthermore, sensitivity studies reveal that surface skin temperature simulations of Greenland would be significantly improved if the more accurate surface height is used. The problem of the height used in current global climate model is mainly due to the fact that the model has to use coarse grid size, and within one grid, land surface height has high heterogeneity. How to assign a proper surface height for each model grid and meanwhile adequately present the high heterogeneity of land surface is a great challenge in current model development.

Black shale, grey shale, fossils and glaciers: Anatomy of the Upper Ordovician–Silurian succession in the Tazzeka Massif of eastern Morocco

A 400 m thick clastic succession of Late Ordovician through Silurian age crops out in the Tazzeka Massif, eastern Morocco. Biostratigraphic data (chitinozoa, acritarchs) constrain these rocks to the Late Katian through Hirnantian (coeval with glaciation in Gondwana), with a ~ 8 Myr hiatus at the Ordovician–Silurian boundary. Sedimentological analysis reveals six facies associations, including interbedded black and grey shale couplets (poorly oxygenated shelf sediments), a bioturbated shale with wave rippled sandstone (inner shelf deposits), several occurrences of diamictite (of probable glaciogenic origin), interbedded sandstone and mudstone (storm and fair-weather wave agitated shoreface), rippled sandstone (storm return flow deposits) and amalgamated sandstone deposits (delta-front debris flows). Direct evidence for glaciation in the Hirnantian deposits is poor. Third order sequence stratigraphic analysis reveals two transgressive systems tracts (Late Katian and intra-Hirnantian), two highstand systems tracts (both intra-Hirnantian), lowstand wedges probably corresponding to two principal glacial lowstands, two maximum flooding surfaces (Late Katian and intra-Hirnantian), and a major ravinement surface (Hirnantian–Silurian contact). Remote from the centre of glaciation, the Tazzeka succession is suggested to be an excellent reference section with which to understand glacially-moderated sea-level changes in the Late Ordovician. Silurian (Late Llandovery or younger) shale geochemistry indicates organic enrichment (TOC > 4.5%). This organic enrichment greatly increases the known extent of the upper of two Silurian organic shales across North Africa (potential hydrocarbon source rocks) across the region.

Variaciones recientes del lóbulo Zapata Sur, Glaciar Tyndall: Campo de Hielo Patagónico Sur (Chile)

A working group of CEQUA and Direccion de Programas Antarticos (DPA) of Universidad de Magallanes, has made several glaciological campaigns in a sector of Tyndall glacier called Zapata Sur lobe. Recent variations of this sector could be associated to the climatic change detected in the region. Results obtained since March of 2003 are reported. Ice thickness measurements with a radio-echo sounding system show thicknesses between 63m, near the East present margin of the ice, and 617m towards the center of glacier, at a distance of 2.5km to the East margin. GPS measurements made in 5 ablation stakes show an average ice thinning of 2.63m, between March 2002 and November 2003. In the surroundings of the East ice margin a surface speed of 1 8 m a-1 was detected, in a sector located approximately at 3km to the West of the ice margin the speed of the surface ice flow is of the order of 2 70 m a-1

Two Tyrrells cross the Barren Lands of Canada, 1893

Abstract In May 1893 Joseph and James Tyrrell, sons of an Irish immigrant to Canada, left Edmonton in Canada's Northwest Territories with a group of voyageurs, partly aided by an aboriginal map and First Nations guides. By January 1894 the team had reached Winnipeg, Manitoba, completing the first expedition through the last large unexplored area of the mainland of Canada. The travellers suffered from many dangers, and the expedition was more than three months overdue when its members arrived at York Factory. Some specimens were lost, but records and photographs acquired on the expedition form an important record of northern exploration. Joe Tyrrell identified the Keewatin centre of glaciation, and the post-glacial extension of the Hudson Bay basin is now known as the Tyrrell Sea. There was criticism at the apparent lack of economic benefit, but Tyrrell located iron ore and a possible copper-bearing area, and his work led indirectly to a productive nickel mine and the present working of diamonds. Tyrrell also documented the huge caribou herds, and the lives of the Inuit that depended on them.

Strong feedbacks between hydrology and sliding of a small alpine glacier

We report the spatial and temporal pattern of sliding on the 7‐km‐long Bench Glacier, Alaska. Using five continuously recording GPS antennas following motion of the surface ice, distributed at 1 km spacing along the glacier center line, we documented surface ice motion over 50 days during summer 2002. Surface speeds in two previous winters constrain the motion component associated with ice deformation, allowing isolation of the sliding speed history. We observed two speedup events bracketing 2 weeks of steady slow sliding. The first event was not associated with a meteorological trigger, was more subtle than the second, and propagated up‐glacier at a rate of several hundred meters per day. The second event coincided with a warm up‐valley wind, which triggered considerable melt of the glacier surface. Sliding speeds in this event reached 0.3 m d−1 and began almost simultaneously at all sites in the ablation area. Both the horizontal and vertical displacement time series can be explained by growth and collapse of cavities in the lee of bumps in the bedrock bed. Cavities grow during rapid sliding and decay by viscous creep. We posit that effective pressure, averaged over some large area of the bed, is inversely proportional to the sliding speed. This effective pressure then controls the collapse rate of cavities, whose dimensions are estimated from a plausible, stepped‐bed geometry. This model explains well the horizontal and vertical surface displacement history through the first event and beginning of the second event. The vertical record demands a substantial and abrupt drop in water pressure that departs from the posited sliding‐effective pressure relationship. We argue that this pressure drop reflects establishment of efficient subglacial drainage, also manifested in a nearly simultaneous step increase in water discharge in the exit stream. The establishment of an efficient conduit system terminates sliding; its maintenance inhibits further sliding over the remainder of the summer.

Spatial variability in water content at the cold‐temperate transition surface of the polythermal Storglaciären, Sweden

The volume fraction of liquid water in temperate glacier ice is important not only for the flow of glaciers and the analysis and processing of ground penetrating radar data from glaciers but also for the stability of the thermal layering in polythermal glaciers. However, little is known about the spatial variations of water content in glaciers. We use relative backscatter strength of ground‐penetrating radar signals to estimate the spatial distribution of water content close to the cold‐temperate transition on Storglaciären, northern Sweden, in an area close to the equilibrium line. The values of relative backscatter strength are calibrated using determinations of absolute water content from temperature measurements across the cold‐temperate transition and the thermodynamic boundary condition at the freezing front. The results show a water content of 0.80%, 0.75%, and 0.58% at three calibration points and a mean water content of 0.8% with a standard deviation of ±0.26% for the extrapolated water content. The extrapolated water content shows a distinct pattern, with lower water content on one side of the glacier center line and higher water content on the other side, with higher water content on the northern side. We hypothesize that the different water contents result from the fact that the ice on either side of the center line originates from different cirques, thus implying spatial variations in the entrapment of water in the firn‐ice transition process in the different cirques.

Temperatures at the base of the Laurentide Ice Sheet inferred from borehole temperature data

We use temperature profiles from 4 deep (>1600 m) boreholes across Canada to determine ground surface temperature histories (GSTH's) through and after the Last Glacial Maximum (LGM). Inversion yields the temperature history at the base of the glacier and the surface temperature evolution after the glacial retreat. The results indicate geographic differences in basal temperature history across the Ice Sheet. During the Last Glacial Maximum, temperatures at the base of the Ice Sheet were lower in eastern Canada, at the southeastern edge of the glacier, than in central Canada, southwest of the glacier center. At all sites, basal temperatures were above the melting point of ice during and after the LGM, which may explain the highly unstable character of the Ice Sheet. The GSTH's are consistent with information on the history of the Laurentide ice sheet and provide quantitative constraints on glacier flow dynamics.

Evidence for rapid retreat and mass loss of Thwaites Glacier, West Antarctica

AbstractThwaites Glacier, the second largest ice stream in West Antarctica, drains an area of 166 500 ± 2000 km2 which accumulates 55 ± 5 Gt a−1 (or 60 ± 6 km3 ice a−1) into the Amundsen Sea, unrestrained by an ice shelf. Using interferometric synthetic-aperture radar (InSAR) data collected by the European Remote-sensing Satellites (ERS-1 and -2) in 1996, an output flux of 71 ±7 Gt a−1 (or 77 ± 8 km3 ice a−1) is estimated at the grounding line, where ice thickness is deduced from hydrostatic equilibrium. A similar flux, 70 ± 7 Gt a−1 (or 76 ± 8 km3 ice a−1), is obtained at a gate located 20 km upstream, where ice thickness was measured in 1978 by ice-sounding radar. Total accumulation in between the two gates is 1.6 Gt a−1, or 1.8 km3 ice a−1. Ice discharge therefore exceeds mass accumulation by 30 ± 15%, and Thwaites Glacier must be thinning and retreating at present. The InSAR data show that the glacier floating ice tongue exerts no back pressure on the inland ice, calves into tabular icebergs along a significant fraction of its grounding line, and has a grounding-line thickness which exceeds a prior-calculated limit for stability. Glacier thinning is confirmed at the coast by the detection of a 1.4 ± 0.2 km retreat of its grounding line between 1992 and 1996 with InSAR, which implies 3.2 ± 0.6 m ice a−1 thinning at the glacier center and less near the sides. These results complement the decimeter-scale annual surface lowering observed with satellite radar altimetry several hundred km inland of the grounding line. The magnitude of ice thinning estimated at the coast, however, rules out temporal changes in accumulation as the explanation for surface lowering. Ice thinning must be due to changes in ice flow.

Responses of Stable Bay-Margin and Barrier-Island Systems to Holocene Sea-Level Highstands, Western Gulf of Mexico

ABSTRACT The microtidal, wave-dominated coast of the western Gulf of Mexico displays a variety of Holocene geomorphic features indicating higher-than-present water levels that were previously attributed to storm processes while geoidal sea level was at its present position. Field and aerial-photograph examinations of bay margins, barrier islands, and beach-ridge plains following major hurricanes show that the elevated features are inundated periodically by high storm surge. Despite their inundation, these highstand features are not modified by modern storm processes. Instead, storm-related erosion and deposition are always seaward of and lower than the highstand features and are always limited to the extant shorezone, where elevations typically are less than 1.5 m above present sea level. Bay-margin and lagoonal highstand indicators include raised marshes and subtidal flats, wave-cut benches, abandoned wave-cut scarps with fringing marshes and/or beach ridges, and accretionary islands and recurved spits. Other emergent marine features include abandoned compound flood-tidal delta and washover fan complexes attached to barrier islands and anomalously high beach ridges within both the barrier-island complexes and beach-ridge plains. The highest beach ridges, raised marshes and flats, and erosional scarps and benches are manifestations of one or more rising phases and highstands in sea level, whereas the lower marshes and accretionary topography are mainly products of the falling phases and shoreface adjustment to present sea level. Different elevations of beach-ridge sets, discordant truncation of beach ridges, and elevated marine- and brackish-water faunal assemblages preserved in beach ridges, raised marshes and flats, and natural levees are compelling evidence of sea-level fluctuations of ±1 to 1.5 m from about 5500 to 1200 cal yr BP. Independent evidence from studies of geodynamic, climatic, and glacio-eustatic processes can explain the mid-Holocene highstands and late Holocene lowering of sea level that is observed in tectonically stable coastal regions far from former centers of glaciation.

Mass balance of the northeast sector of the Greenland ice sheet: a remote-sensing perspective

AbstractSynthetic-aperture radar interferometry data and airborne ice-sounding radar (ISR) data are employed to obtain modern estimates of the inland ice production from Nioghalvfjerdsbræ (NB) and Zachariae Isstrøm (ZI), the two largest glaciers draining the northeast sector of the Greenland ice sheet. Ice fluxes are measured at the grounding line (14.2 ±1 km3ice a−1for NB and 10.8 ±1 km3ice a−1for ZI) with an ice thickness deduced from ice-shelf hydrostatic equilibrium, and along an ISR profile collected upstream of the grounding line (14.3 ± 0.7 km3ice a−1for NB and 11.6 ± 0.6 km3ice a−1for ZI). Balance fluxes calculated from a map of snow accumulation and model predictions of surface melt are 11.9 ± 2 km3ice a−1for NB and 10.0 ± 2 km3ice a−1for ZI at the grounding line, and 12.2 and 10.3 km3ice a−1, respectively, at the ISR line. The two glaciers therefore exhibit a negative mass balance equivalent to 14% of their balance flux, with a ±12% uncertainty. Independently, we detect a retreat of the grounding line of NB between 1992 and 1996 which is larger at the glacier center (920 ± 250 m) than on the sides (240 ± 50 m). The corresponding ice-thinning rates (2 ± 1 m a−1at the glacier center and 0.6 ± 0.3 m a−1on the sides) are too large to be accommodated by temporal changes in ablation or accumulation, and must be due to dynamic thinning.

Glacier mass-balance determination by remote sensing and high-resolution modelling

AbstractAn indirect methodology for determining the distribution of mass balance at high spatial resolution using remote sensing and ice-flow modelling is presented. The method, based on the mass-continuity equation, requires two datasets collected over the desired monitoring interval: (i) the spatial pattern of glacier surface-elevation change, and (ii) the mass-flux divergence field. At Haut Glacier d’Arolla, Valais, Switzerland, the mass-balance distribution between September 1992 and September 1993 is calculated at 20 m resolution from the difference between the pattern of surface-elevation change derived from analytical photogrammetry and the mass-flux divergence field determined from three-dimensional, numerical flow modelling constrained by surface-velocity measurements. The resultant pattern of mass balance is almost totally negative, showing a strong dependence on elevation, but with large localized departures. The computed distribution of mass balance compares well (R2 = 0.91) with mass-balance measurements made at stakes installed along the glacier centre line over the same period. Despite the highly optimized nature of the flow-modelling effort employed in this study, the good agreement indicates the potential this method has as a strategy for deriving high spatial and temporal-resolution estimates of mass balance.

Quiescent-phase changes in velocity and geometry of Finsterwalderbreen, a surge-type glacier in Svalbard

Finsterwalderbreen is a 35 km2, polythermal glacier in southern Spitsbergen, which last surged at around the start of the 20th century, and is still in the quiescent phase. Surface elevations measured several times since 1898 show strong thinning and retreat at the front, and gradual build-up in the accumulation area. Present-day annual velocities increase from about 1 m a–1 at the snout to a maximum of 13 m a–1 near the equilibrium line, then drop to 5 m a–1 at the bergschrund. Summer velocities are higher than the annual average, and winter velocities are lower (10–60% of summer velocities, where both are measured over several months). Velocities measured along the glacier centre line in 1950–52 are higher than those measured in 1994–95 in the upper basin, but are lower in the ablation area, which may be attributable to changes in surface profile on recovery from the surge. The measured modern ice flux (≈2.5 x 10–3 km3 a–1 w.e.) is only about 60% of the flux required to maintain balance (≈4.1 x 10–3 km3 a–1 w.e.), as determined from continuing mass-balance studies. Multi-frequency radar profiles show that most of the glacier is at the pressure-melting point at the base. This is consistent with hydrological studies showing high suspended-sediment loads, and hydro-chemical evidence of high sulphate levels, both indicating a well-developed basal drainage system during the summer which probably accounts for the seasonal velocity variations. Since the glacier still has a temperate bed, and appears to be building up in the accumulation area, it may be developing towards another surge.

Quiescent-phase changes in velocity and geometry of Finsterwalderbreen, a surge-type glacier in Svalbard

Finsterwalderbreen is a 35 km2, polythermal glacier in southern Spitsbergen, which last surged at around the start of the 20th century, and is still in the quiescent phase. Surface elevations measured several times since 1898 show strong thinning and retreat at the front, and gradual build-up in the accumulation area. Present-day annual velocities increase from about 1 m a–1 at the snout to a maximum of 13 m a–1 near the equilibrium line, then drop to 5 m a–1 at the bergschrund. Summer velocities are higher than the annual average, and winter velocities are lower (10–60% of summer velocities, where both are measured over several months). Velocities measured along the glacier centre line in 1950–52 are higher than those measured in 1994–95 in the upper basin, but are lower in the ablation area, which may be attributable to changes in surface profile on recovery from the surge. The measured modern ice flux (≈2.5 x 10–3 km3 a–1 w.e.) is only about 60% of the flux required to maintain balance (≈4.1 x 10–3 km3 a–1 w.e.), as determined from continuing mass-balance studies. Multi-frequency radar profiles show that most of the glacier is at the pressure-melting point at the base. This is consistent with hydrological studies showing high suspended-sediment loads, and hydro-chemical evidence of high sulphate levels, both indicating a well-developed basal drainage system during the summer which probably accounts for the seasonal velocity variations. Since the glacier still has a temperate bed, and appears to be building up in the accumulation area, it may be developing towards another surge.

Late Cenozoic history of the Scandinavian and Barents Sea ice sheets

The oldest ice rafted material (IRD) on the Vøring Plateau is dated to about 11 Ma, and is regarded as evidence that glaciers extended to sea level somewhere around the Nordic Sea at this time. We estimate that the major glaciations of Scandinavia and the Barents Sea-Svalbard area started at 2.5–2.8 Ma, when the amount of IRD on the Vøring Plateau increased strongly, the deep sea δ 18O curves indicate that onset of Northern Hemisphere glaciations, and the climate in The Netherlands was so cold that a major glaciation of Scandinavia is inferred. Most of the time until 0.9 Ma, the ice sheets were of intermediate size; they probably reached the coastal zone of western Norway for long periods. The center of glaciation is inferred to have been further north than during the later glaciations, and we speculate that this was the period of maximum glacial erosion of the Barents Sea. The largest glaciations, and also the warmest interglacials occurred during the last 900 kyrs, when the 100 kyr astronomic cycle became important. For the last glaciation, the Weichselian, the glacial fluctuations are known in greater detail both for Scandinavia and the Svalbard-Barents Sea region. In Scandinavia the glacial fluctuations apparently followed the 23 kyr precession cycle, whereas in the Barents Sea they followed the 41 kyr tilt cycle. In both areas more than one advance reached beyond the coast. We use the Weichselian record to “calibrate” the interpretation of more indirect evidences of glacial fluctuations, and apply the latter to the Scandinavian and Barents Sea glacial history since 2.5 Ma.

A distributed surface energy-balance model for a small valley glacier. I. Development and testing for Haut Glacier d’ Arolla, Valais, Switzerland

AbstractThis paper describes the development and testing of a distributed surface energy-balance model used to calculate rates of surface melting at Haut Glacier d’Arolla, Valais, Switzerland. The model uses a digital elevation model (DEM) of the glacier surface and surrounding topography together with meterological data collected at a site in front of the glacier to determine hourly or daily totals of the energy-balance components and hence of melting over the entire surface of the glacier with a spatial resolution of 20 m. The model can also be used to determine temporal and spatial variations in snow depth, snow-line position and glacier surface albedo. Calculations from the model are compared with observations made along the glacier centre line 1990, and in general the model performs very well. The correlation coefficients between calculated and measured snow-line elevation, albedo and ablation are 0.99, 0.85 and 0.81, respectively. The main source of error between modelled and measured values of these variables is probably inadequacies in the parameterization of albedo used in the model.

A distributed surface energy-balance model for a small valley glacier. I. Development and testing for Haut Glacier d’ Arolla, Valais, Switzerland

AbstractThis paper describes the development and testing of a distributed surface energy-balance model used to calculate rates of surface melting at Haut Glacier d’Arolla, Valais, Switzerland. The model uses a digital elevation model (DEM) of the glacier surface and surrounding topography together with meterological data collected at a site in front of the glacier to determine hourly or daily totals of the energy-balance components and hence of melting over the entire surface of the glacier with a spatial resolution of 20 m. The model can also be used to determine temporal and spatial variations in snow depth, snow-line position and glacier surface albedo. Calculations from the model are compared with observations made along the glacier centre line 1990, and in general the model performs very well. The correlation coefficients between calculated and measured snow-line elevation, albedo and ablation are 0.99, 0.85 and 0.81, respectively. The main source of error between modelled and measured values of these variables is probably inadequacies in the parameterization of albedo used in the model.

The drumlin fields of the Novaya Zemlya‐Urals region and the Kara Sea center of glaciation

Abstract Assemblages of drumlins, crag‐and‐tail features, giant glacial grooves, and megaflutes—collectively termed “drumlin fields"—are described along the southwestern shorelines of the Kara Sea, i.e., southernmost Novaya Zemlya, Vaygach Island, the Yugorskiy Peninsula, and the Pay‐Khoy ridge. All these landforms were formed during one of the latest stages in glaciation in the Eurasian Arctic, radiocarbon dated at about 8.5 thousand years ago. At that late stage, the ice kept spreading out of the Kara Sea center, which is strongly suggested by the NE‐SW orientation of the landforms. This is consistent with the model of a continuous marine Eurasian ice sheet and contradicts the concepts of “restricted” and “diachronous” glaciation. The Kara center of glaciation turns out to be one of the most stable and long‐lived features of the Northern Hemisphere's glaciation.

Paleoecology of the Arcto‐Atlantic during the Holocene

Abstract New paleoecological reconstructions are based on results of integrated investigations of a Holocene site in lower Gr⊘ndalen near Barentsburg, Spitsbergen. Fluvial, solifluctional, lacustrine, paludine (marsh environment), and marine facies give evidence of complex environmental changes. A mosaic of large grass‐moss fens and sphagnum‐hypnum palsa bogs together with dwarf shrub‐moss heaths existed during the Holocene Climatic Optimum. Solifluction processes occurred during minor cool intervals and led to the formation of lobes and fans on valley slopes. Herbaceous and hypnum‐moss swamps and moist meadows occurred during a rather warm climate in the Subboreal. There was a marked marine transgression in the early Subatlantic. Correlations were made between the main stages of environmental development in Spitsbergen, the Faroes, the Shetland Islands, eastern Greenland, and Novaya Zemlya. During the last ice age these areas supported centers of glaciation in combination with biotic refugia, where successional systems of plants were highly organized. Since late‐glacial time these systems have displayed relatively rapid dispersal to new sites as they became free of ice and water.

Intra-seasonal changes in deformation profiles revealed by borehole studies, Storglaciären, Sweden

AbstractIn 1985, 1987 and 1988, we measured deformation of boreholes in the ablation zone of Storglaciären. A different hole was used each year. Deformation profiles were determined for four consecutive time periods between mid-July and early September. All three holes were in an area where the glacier lies in an overdeepened part of the bed, up-glacier from a riegel. The first hole was approximately on the glacier center line while the others were midway between the center line and one or the other margin. Despite large standard errors, variations in the deformation profiles during the melt season are broadly consistent with other data. We thus believe that they are real, and that they reflect changes in the stress field resulting from changes in drag at the bed. A decrease in drag early in the melt season, coupled with convergence of the bed contours towards the riegel, is believed to be responsible for a previously documented increase in vertical velocity just up glacier from the riegal at this time of year. Also noteworthy, but perhaps problematical, was an abrupt transverse shear of at a depth of ~25 m near the center of the glacier in July 1985. The shear took place in the zone in which cold ice near the surface gives way to temperate ice deeper in the glacier.