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ABSTRACT Streamlined features, rat-tails, glacial striae, and dispersal patterns for till clasts and matrix geochemistry define glacier dynamics and flow directions across the Petitcodiac map area, southeastern New Brunswick. These [...]

A method is presented for calculating longitudinal glacier strain rates directly from the wrapped phase of an interferometric synthetic aperture radar (InSAR) interferogram assuming the ice flow path is known. This technique enables strain rates to be calculated for scenes lacking any velocity control points or areas within a scene where the phase is not continuously unwrappable from a velocity control point. The contributions to the error in the estimate of the strain rate are evaluated, and recommendations for appropriate SAR and InSAR parameters are presented. An example using Radarsat-1 InSAR data of an East Antarctic ice stream demonstrates the technique for calculating longitudinal strain rate profiles and estimating tensile strength of ice (186-215 kPa) from locations of crevasse initiation. The strain rate error was found to be 17% corresponding to a tensile strength of ice error of 5.3% Index Terms--Glaciers, interferometric synthetic aperture radar (InSAR), interferometry.

Glacier wastage has been pervasive during the last century; small glaciers and those in marginal environments are disappearing, large mid-latitude glaciers are shrinking slightly, and arctic glaciers are warming. Net mass balances during the last 40 years are predominately negative and both winter and summer balances (accumulation and ablation) and mass turnover are increasing, especially after 1988. Two principal components of winter balance time-series explain about 50% of the variability in the data. Glacier winter balances in north and central Europe correlate with the Arctic Oscillation, and glaciers in western North America correlate with the Southern Oscillation and Northern Hemisphere air temperature. The degree of synchronization for distant glaciers relates to changes in time of atmospheric circulation patterns as well as differing dynamic responses.

The detection and quantification of surface deformation of an active rock glacier using the differential synthetic aperture radar (SAR) interferometry (D-InSAR) technique is presented. An average deformation rate of -6 mm/35 days in the radar line of ight was estimated for the summer of 1992. The maximum deformation rate, -18 mm/35 days, was identified at the upper part of the rock glacier, whereas the deformation rate at the snout of the rock glacier was about -10 mm/35 days. The spatial distribution of the surface deformation in the D-InSAR displacement map is smooth and supports the idea that ice is the stress-transferring medium in rock glaciers. Index Terms--Differential synthetic aperture radar interferometry (D-InSAR), mountain permafrost creep, rock glaciers, synthetic aperture radar (SAR) interferometry.

A modeling system for investigating meteorological controls on glacier mass balance is described and applied to the Southern Patagonian Icefield. Output from a mesoscale atmospheric model is used to drive a glacier mass balance model using model precipitation and turbulent fluxes adjusted to account for the unrealistically low surface elevations of the icefield in the atmospheric model. Simulations of January and July conditions produce glacier equilibrium line altitudes (ELAs) that are higher than the observed, but the ELA gradient is realistically simulated. The high ELAs are primarily due to underestimates of vertical temperature gradients in the atmospheric model and uncertainties in the ablation season length. The model shows that both winter and summer precipitation, as well as summer temperatures, are important determinants of the mass balance of the Southern Patagonia glaciers. The position of the icefield on the continent is also relevant. On the western side of the icefield, precipitation rates are high and dominate the mass balance calculation. In the east, ablation is much more important for determining the mass balance, and this introduces an enhanced sensitivity to atmospheric temperature, wind speed, and atmospheric moisture levels.

Surface exposure ages of glacial deposits in the Ford Ranges of western Marie Byrd Land indicate continuous thinning of the West Antarctic Ice Sheet by more than 700 meters near the coast throughout the past 10,000 years. Deglaciation lagged the disappearance of ice sheets in the Northern Hemisphere by thousands of years and may still be under way. These results provide further evidence that parts of the West Antarctic Ice Sheet are on a long-term trajectory of decline. West Antarctic melting contributed water to the oceans in the late Holocene and may continue to do so in the future., Melting of ice sheets at the end of the last glacial period raised the world's oceans by about 120 m between 19,000 and 6000 years ago (1). Antarctica's contribution is [...]

Ice flow at a location in the equilibrium zone of the west-central Greenland Ice Sheet accelerates above the midwinter average rate during periods of summer melting. The near coincidence of the ice acceleration with the duration of surface melting, followed by deceleration after the melting ceases, indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice-bedrock interface. Interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting, with larger increases accompanying higher amounts of summer melting. The indicated coupling between surface melting and ice-sheet flow provides a mechanism for rapid, large-scale, dynamic responses of ice sheets to climate warming., The time scale for dynamic responses of ice sheets to changes in climate (e.g., snow accumulation and surface temperature) is typically considered to be hundreds to thousands of years (1). [...]

Here we report previously undescribed features of erosion and deposition by a cold (polar) glacier. A recent study challenged the assumption that cold glaciers neither slide nor abrade their beds, but no geological evidence was offered. The features we describe include abrasion marks, subglacial deposits, glaciotectonically deformed substrate, isolated blocks, ice-cored debris mounds, and boulder trains, all products of a recent cold ice advance and retreat Mapping these features elsewhere in Antarctica will document recent shifts in the East Antarctic Ice Sheet margin, providing new insight on regional mass-balance changes. Keywords: cold-based glaciers, abrasion, Allan Hills, Antarctic ice sheet, glacial deposition.

Variability in iceberg discharge and deep-ocean circulation in the North Atlantic during the last glacial period is inferred from the grain-size distribution and trace elemental composition of terrigenous sediments in a deep-sea core taken on Reykjanes Ridge, south of Iceland. End-member modeling of the grain-size distributions is used to unmix the signals of varying bottom-current speed and iceberg discharge. The size distribution within the silt fraction appears to be influenced by both factors. Based on Th-Sc-La relationship, we established that during the ice-rafted detritus events, continental material of likely Greenlandic origin increased to 87%, and that bottom-current-derived material contains to 40% mid-oceanic ridge fines, probably of Icelandic origin. Our results have important implications for the use of silt grain size as an indicator for paleocurrent speed in the glacial North Atlantic. We show that reconstructions of variations in bottom-current speed based on the raw grain-size data are opposite to inferences from the unmixed record. The latter indicates that deep-water convection decreased during periods of enhanced iceberg discharge, which is in general agreement with paleoceanographic reconstructions of the North Atlantic. Keywords: ocean circulation, iceberg discharge, brain-size distribution, end-member modeling, trace element geochemistry.

The main inflow of deep water to the Pacific is via a deep western boundary current. As the current passes along the continental margin off eastern New Zealand, it receives much terrigenous sediment, which, together with the biogenic pelagic supply, has been reworked into a suite of large drifts. Ocean Drilling Program Site 1123 on the North Chatham Drift and Site 1124 on the Rekohu Drift have yielded high-resolution and well-dated records of carbonate and terrigenous fluxes for the past 3 m.y. Deposition at both drifts was affected by a deep western boundary current background sediment flux and by glacial-interglacial cycles. In addition, drifts received site-specific flux pulses caused by (1) sediment remobilization under a vigorous Antarctic Circuumpolar Current, (2) increase oceanic productivity, (3) overspill of sediment from the newly formed Hikurangi Channel, and (4) generally increased discharge from the Hikurangi Channel under intensified Quaternary uplift and paleoclimatic oscillations. Keywords: southwest Pacific, mass accumulation rates, deep western boundary current, Ocean Drilling Program, sediment drifts.

We present evidence of glaciohydraulic supercooling under jokulhlaup and ablation-dominated conditions from two temperate Icelandic glaciers. Observations show that freezing of sediment-laden meltwater leads to intraglacial debris entrainment during normal and extreme hydrologic regimes. Intraglacial frazil ice propagation under normal ablation-dominated conditions can trap copious volumes of sediment, which forms anomalously thick sections of debris-rich ice. Glaciohydraulic supercooling plays an important role in intraglacial debris entrainment and should be given more attention in models of basal ice development. Extreme jokulhlaup conditions can result in significant intraglacial sediment accretion by supercooling, which may explain the concentration of englacial sediments deposited in Heinrich layers in the North Atlantic during the last glaciation. Keywords: jokulhlaups, glaciofluvial sedimentation, accretion, hydraulic fracturing, Iceland.

A 420-year history of strontium/calcium, uranium/calcium, and oxygen isotope ratios in eight coral cores from the Great Barrier Reef, Australia, indicates that sea surface temperature and salinity were higher in the 18th century than in the 20th century. An abrupt freshening after 1870 occurred simultaneously throughout the southwestern Pacific, coinciding with cooling tropical temperatures. Higher salinities between 1565 and 1870 are best explained by a combination of advection and wind-induced evaporation resulting from a strong latitudinal temperature gradient and intensified circulation. The global Little Ice Age glacial expansion may have been driven, in part, by greater poleward transport of water vapor from the tropical Pacific., The Little Ice Age (LIA) appears in most Northern Hemisphere paleoclimate reconstructions as multiple, century-scale periods of anomalously cold, dry conditions between the 15th and late 19th centuries (1-4). Glacial [...]

The stratigraphical and structural continuity of the Late Proterozoic Dalradian rocks of the Scottish Highlands is re-examined in the light of new U--Pb zircon ages on the tuffs belonging to the Tayvallich Volcanic Formation (601 [+ or -] 4 Ma), and on the late Grampian `Newer Gabbros' (470 [+ or -] 9 Ma) of Insch and Morven-Cabrach in Aberdeenshire. These age data, together with the existing 590 [+ or -] 2 Ma age for the Ben Vuirich Granite, provide key radiometric constraints on the evolution of the Dalradian block, and the implications arising from these ages are critically assessed. Three main conclusions are drawn. (1) The entire Caledonian orogeny, although short-lived, is unlikely to have affected sediments of Arenig age and a break probably occurs between those Dalradian sediments of late Proterozoic ( (2) A period of crustal thickening probably affected some Dalradian rocks prior to 590 Ma. Such an event is indicated by both the polymetamorphic histories of the lower parts of the Dalradian pile and the contact metamorphic assemblages within the aureole of the Ben Vuirich Granite, which are incompatible with sedimentary thicknesses. (3) Age constraints on global Late Proterozoic glacial activity also suggest that the Dalradian stratigraphy is broken into discrete smaller units. Models involving continuous deposition of Dalradian sediments from pre-750 Ma to 470 Ma are rejected. Keywords: Dalradian Orogeny, Neoproterozoic, glaciation, U--Pb, zircons.

Age-depth relations from internal layering reveal a large region of rapid basal melting in Greenland. Melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet. Locally, high melt rates indicate geothermal fluxes 15 to 30 times continental background. The southern limit of melt coincides with magnetic anomalies and topography that suggest a volcanic origin., Basal melt and meltwater exert a strong influence on ice flow (1-4). Our limited knowledge of basal melt is derived from models and sparse observations of bed properties (5-7). Here [...]

The lower Illinois River Basin (LIRB) covers 47,000 [km.sup.2] of central and western Illinois. In the LIRB, 90% of the ground water supplies are from the deep and shallow glacial drift aquifers. The deep glacial drift aquifer (DGDA) is below 152 m altitude, a sand and gravel deposit that fills the Mahomet Buried Bedrock Valley, and overlain by more than 30.5 m of clayey till. The LIRB is part of the USGS National Water Quality Assessment program, which has an objective to describe the status and trends of surface and ground water quality. In the DGDA, 55% of the wells used for public drinking-water supply and 43% of the wells used for domestic drinking water supply have arsenic concentrations above 10 µg/L (a new U.S. EPA drinking water standard). Arsenic concentrations greater than 25 µg/L in ground water are mostly in the form of arsenite (AsIII). The proportion of arsenate (AsV) to arsenite does not change along the flowpath of the DGDA. Because of the limited number of arsenic species analyses, no clear relations between species and other trace elements, major ions, or physical parameters could be established. Arsenic and barium concentrations increase from east to west in the DGDA and are positively correlated. Chloride and arsenic are positively correlated and provide evidence that arsenic may be derived locally from underlying bedrock. Solid phase geochemical analysis of the till, sand and gravel, and bedrock show the highest presence of arsenic in the underlying organic-rich carbonate bedrock. The black shale or coal within the organic-rich carbonate bedrock is a potential source of arsenic. Most high arsenic concentrations found in the DGDA are west and downgradient of the bedrock structural features. Geologic structures in the bedrock are potential pathways for recharge to the DGDA from surrounding bedrock., Kelly L. Warner (1) Introduction The deep glacial drift aquifer (DGDA) in central Illinois is a sand and gravel deposit that fills the Mahomet Buried Bedrock Valley (MBBV) and overlain [...]

Stratigraphic and geomorphic data defined by radiocarbon ages, tree-ring dates, and historical observations provide evidence of three major Holocene expansions of Hubbard Glacier. Early in each advance the Hubbard Glacier margin blocked Russell Fiord to create Russell lake, raising base level and causing stream beds and fan deltas throughout the Russell drainage basin to aggrade. Each Hubbard Glacier expansion continued with an ice lobe advancing through Disenchantment and Yakutat Bays in the west, and an eastern lobe advancing into Russell Fiord. The earlier two Holocene expansions were, respectively, under way at 7690 and 5600 calibrated yr B.P., and each advance culminated more than 1 k.y. later. The late Holocene advance was under way by 3100 yr ago and reached ~13 km farther south in Russell Fiord than the preceding two expansions. Late Holocene deglaciation of Yakutat and Disenchantment Bays was complete before A.D. 1791; Nunatak Glacier flowing from neves east of Russell Fiord became the primary ice source to the Russell Fiord lobe at or before this date. Ice retreat from the southern end of Russell Fiord began in the late eighteenth century and the penultimate Russell lake drained ca. A.D. 1860. The relatively slow advances and more rapid retreats of Hubbard Glacier are consistent with the model of the iceberg-calving glacier cycle. Hubbard Glacier is currently advancing and will likely reestablish Russell lake in the near future, affecting local fisheries. However, glacier lobes are unlikely to reach the area of the town of Yakutat, built on late Holocene glacial deposits, in the next 1 k.y. Keywords: Fan deltas, glacial geology, glacial lakes, tidewater glaciers, Yakutat Bay.

Glacial meltwaters after a storm can contribute bacteria to the streams, mostly Archaea and bacteria of the Cytophaga-Flavobacterium group. Streams have higher growth rates and greater bacterial carbon production following a glacial melt.

The flow system existing during Pleistocene glaciation of the Williston basin in Manitoba suggests modern pressure distributions may not be reliable substitutes for ancient petroleum pathways. This region experienced a large enough influx of fresh water to reverse the regional-scale flow.

Field evidence in the Koryak Mountains-Lake Mainitz region of far eastern Russia supports three Pleistocene glacial advances. The early Wisconsinan and pre-Wisconsinan glaciations are represented by broad lobate moraines extending as much as 30 km north of the Koryak Mountains. Field evidence demonstrates that the terminal, lateral, and medial moraines, as well as meltwater channels, dead ice topography, kettles, and out-wash plains mark the extent of ice during the last glacial maximum (LGM), during which glaciers reached no more than 20 km beyond their present limits. Those emanating from the southern Koryak Mountains may have reached the Bering Sea. Numerical and relative dating techniques support these results and test the theoretical models of the LGM in western Beringia. Erratics on moraines and glaciofluvial terraces, common to all valleys at 13-13.8 m above river level, yield (super 36)Cl exposure ages ranging from 10.08 to 25.78 ka. The Koryak Mountains-Lake Mainitz record of glaciation is spatially and temporally consistent with the glaciation pattern across central Beringia found in other terrestrial and marine records. Glacier growth in the Koryak Mountains was sustained by possible increased summer sea surface temperatures and precipitation in the northwest Pacific region. Evidence from the northern Koryak Mountains (lat 64 degrees N, long 177 degrees E) indicates that the extent of ice in western Beringia was limited to mountain and valley glaciers during the LGM. This field-based research contradicts M.G. Grosswald's theoretical Beringian ice sheet hypothesis. Keywords: Beringia, Chukotka, cosmogenic elements, erratics, glaciation, northwest Pacific.

Many rock glaciers contain massive ice that may be usefull in paleoclimate studies. Interpreting geochemical ice-core records from rock glaciers requires a thorough understanding of rock glacier structure and dynamics. High-precision surface-velocity data were obtained for the Galena Creek rock glacier, Absaroka Mountains, Wyoming. Surface velocities range from 0 to 1.00 m/yr and vary across the rock glacier in a manner similar to true glaciers. We used Glen's flow law to calculate the thickness of the deforming ice layer. The modeled ice thickness ranges from 0 to 50 m, and is confirmed by direct observations. This agreement shows that rock glacier movement can be entirely explained by deformation of massive ice within the rock glacier; neither basal sliding nor deformation of basal debris is necessary. Recovered ice cores (to depths of 25 m) contain thin debris layers associated with summer ablation in the accumulation zone. The ages of four samples of organic material removed from several debris layers in the southern half of the rock glacier range from 200 +/- 40 to 2250 +/- 35(super 14)C yr B.P., demonstrating that the rock glacier formed well before the Little Ice Age and may contain ice dating to the middle Holocene or earlier.

Studies of biotic remains of polar ice caps have been limited to morphological identification of plant pollen and spores. By using sensitive molecular techniques, we now demonstrate a much greater range of detectable organisms; from 2000- and 4000-year-old ice-core samples, we obtained and characterized 120 clones that represent at least 57 distinct taxa and reveal a diversity of fungi, plants, algae, and protists. The organisms derive from distant sources as well as from the local arctic environment. Our results suggest that additional taxa may soon be readily identified, providing a plank for future studies of deep ice cores and yielding valuable information about ancient communities and their change over time.

Humanity has a limited window in which it can hope to avoid the worst effects of climate change, according to climate report.Humanity has a limited window in which it can hope to avoid the more dire effects of climate change, according to climate report., Author(s): Jeff TollefsonAuthor Affiliations:IPCC says limiting global warming to 1.5 °C will require drastic action Glaciers and sea ice won't be safe in a world that warms to 2 °C [...]

Glacial runoff from the Himalayas supplies vital freshwater for agriculture and hydroelectric facilities in mountain regions of India and Nepal. New research has found that the flow of this water [...]

Subglacial drainage systems are inaccessible and their surges are infrequent, and normal field observations only provide limited support for certain models. The major discharge of water from an ice-dammed lake which drains along the glacier bed, can offer the chance to test current hypotheses, as outburst floods during glacial surges can be compared with those occurring during normal periods.

The circular fracture pattern in the Vatnajokull glacier generated by a recent subglacial volcanic eruption was analyzed using methods based on fractal analysis. A crossover analysis based on estimates of the sampling bias showed that the fracture length was proportional to a power of the fracture area, providing a quantitative characterization of patterns of interacting fractures. A simple simulation model reproduces the most important visual and statistical characteristics of the observed fracture pattern. The model can be used to understand and separate the roles of material properties, deformation history, and geometry in geological fracture processes.

Ice coring provides detailed data on past and present climatic changes when used in combination with glacier mass balance measurements. A core sample record dating from 1600-1900 revealed differences between glaciers on Sweden's east and west sides. While eastern glacier sizes are controlled by historically consistent summer temperatures, western glaciers are increasing in mass.