B

Antarctic Peninsula Bathymetric Map

Plate 26.1 Location map of the M'Clintock Channel Ice Stream (a) and satellite imagery of the bedform imprint on Victoria Island (b). The late glacial imprint of the ice stream occupies present day M'Clintock Channel and infringes on western Prince of Wales Island and eastern Storkerson Peninsula (thin red lines). Landsat satellite imagery in (b) shows the margin of the late glacial ice stream imprint on Storkerson Peninsula. However, older flow patterns (thin black lines) indicate that the ice...

Institute of Arctic and Alpine Research and Department of Geography University of Colorado Boulder CO 803090450 USA

Temperate glaciers are noted for exceptionally high erosion rates, which should promote chemical weathering because rates of physical and chemical denudation are generally coupled. Yet fluxes of dissolved cations from glaciers are indistinguishable from non-glacierized basins, and fluxes of dissolved silica are about an order of magnitude lower than from non-glacierized basins (Anderson et al., 1997, Hodson et al., 2000). In this study, I model the solute flux from a glacier to gain insight...

Water source and drainage systems

Subglacial meltwater originates from a range of sources, mainly from melting of ice by geothermal heat trapped at the glacier sole and by the frictional heat caused by ice movement past the substratum. These two sources yield up to some 100 mmyr-1 of water. Close to the ice margin, in the area where englacial conduits extend to the bed, surface ablation water may reach the ice sole with recharge several orders of magnitude greater than the basal meltwater alone. It is difficult to estimate how...

Darrel A Swift

Department of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK At Haut Glacier d'Arolla, Switzerland (Fig. 3.1), suspended sediment transport during the 1998 melt season demonstrates the importance of subglacial drainage system morphology for basal sediment evacuation because it influences both the capacity of meltwater to transport basal sediment and the mechanisms by which sediment is accessed and entrained. Early in the melt season, surface runoff enters a...

Ice dynamics

Besides being used for determining calving fluxes, velocities derived by SAR interferometry have been used to detect glacier surges (Joughin et al. 1996 Mohr et al., 1998), and to infer grounding-line positions and their migration. Rignot et al. (2001) report grounding-line retreat of most north and northeast Greenland floating glaciers between 1992 and 1996. The retreat rate varies from several hundred metres per year up to 1kmyr-1. Rignot et al. (2001) argue that the corresponding glacier...

An analysis of the AWSderived surface fluxes

For the year 2000, all components of the surface energy balance are calculated from the AWS data (Fig. 34.1). Daily mean incoming shortwave radiation shows a clear annual cycle. The day to day variation is due to clouds. In winter, reflected shortwave radiation almost equals incoming shortwave radiation owing to the high surface albedo, which drops in May when snow is starting to melt and ice appears at the surface. The mean annual albedo is 0.53. Incoming longwave radiation is generally less...

Discussion

Do the observed changes in Arctic sea ice, temperature and atmospheric circulation represent natural variability or is there an anthropogenic influence As evaluated over the 20th century, the Arctic has exhibited considerable variability on decadal and mul-tidecadal time-scales. Although a great deal of emphasis has been placed on the recent warming, available records, albeit primarily from inland and coastal stations, document a rise in surface air temperatures from about 1920 to 1940 that was...

Hydrochemical and environmental aspects

In a cycle comprising a glaciation and two bracketing interglacial periods, the predicted changes in groundwater chemistry will be as profound as the changes in groundwater-flow dynamics (Fig. 9.5). Worth noting is isostatic rebound that may cause fracturing and matrix expansion, thereby increasing the rock permeability on a regional scale and enabling migration of new fluids into the substratum after deglaciation (e.g. Weaver et al., 1995). Glacial meltwater recharging the subsurface has...

LIAlike cycles in the Holocene

As the search for forcing mechanisms to explain glacial history on Holocene time-scales intensifies there is a need to ask are there Figure 21.7 Data from Iceland on Little Ice Age (LIA) time-scales. (A) Mann et al. (1999), (B) sea ice and S18O in B997-328, (C) Stykkisholmur winter and summer temperature trends, (D) Siglunes water column temperature and Stykkisholmur mean annual temperature (MAT). periodic LIA-like events within the Holocene (Bond et al., 1999, 2001), and are there recent...

Interaction between groundwater and water in subglacial channels

Where glaciers rest directly on aquifers or are separated from them only by a thin layer of low-permeability sediment, the groundwater is in contact with the water in channels at the ice-bed interface. Channel formation reduces the water pressure and generates a hydraulic gradient, which will drive groundwater from the surrounding sediment into the channel and create a catchment area along the channel. This was suggested independently by Shoemaker & Leung (1987) and Boulton & Hindmarsh...

Background to recent progress

The substantial progress that has been made in subsequent decades is well illustrated in the papers in this volume. One can recognize that progress has been stimulated by both technical developments that have increased the nature and areal coverage of data and the means to analyse them, as well as the emergence of the new theoretical structures of earth system science with its stress on interconnectedness. Remote sensing has opened up new horizons on a revolutionary scale. Whereas fieldworkers...

AMSR 2002presentSwath width 1445 km

Table 73.3 Details of SAR missions suitable for remote sensing of the cryosphere SAR Time period Frequency (GHz) Incidence angle Polarization Table 73.3 Details of SAR missions suitable for remote sensing of the cryosphere SAR Time period Frequency (GHz) Incidence angle Polarization Figure 73.2 Schematic diagram illustrating the geometry of repeat pass synthetic aperture radar interferometry. Ai and Aj are the positions of the satellite at epochs i and j, B is the separation in space, or...

H pgH dx ayox

Where the third term on the left-hand side represents basal traction and is often parameterized using a linear relation to slip velocity (MacAyeal, 1989). In both cases, similar expressions are used for the force balance in the y dimension and, in practice, the equations are solved by using Glen's flow law to substitute the relevant horizontal velocity components for the stress components. Models based around Equation (3) have relatively low computational demands because they are two...

Institute for Marine and Atmospheric Research Utrecht Utrecht University PO Box 80005 3508 TA Utrecht The Netherlands

Over snow and ice, the surface mass balance determines whether the surface loses mass to or gains mass from the atmosphere. The mass balance is the sum of accumulation and ablation. In the case of dry snow surfaces, melt and runoff can be ignored, which means that ablation can take place only through sublimation and wind erosion. Surface sublimation represents the transport of water vapour directly from the snow surface into the atmosphere. Wind erosion occurs when winds are stronger than the...

Results from Vostok

However, when interpreting palaeo-excess records there are even more ambiguities to consider than just evaporation conditions and their exact influence on the double isotopic composition. Currently Antarctic deep-ice drillings cover several glacial-interglacial cycles. The Vostok ice-core provides us with a deuterium excess record spanning now the past ca. 400,000yr (Vimeux et al., 1999, 2001, 2002). Fully interpreting this long-term record, Vimeux et al. (2002) came to an important...

School of Physical and Geographical Sciences Keele University Keele ST5 5BG UK

The study of glaciers has immense significance for understanding and predicting global environmental change. The planet's glaciers are major players in the unfolding drama of the changing environment, and provide a wealth of information about how climate and other components of the Earth system have changed in the past. Scientists from different fields have begun to come together in their common interest in glaciers and the Earth's changing environment, and to recognize the increasing...

Introduction

Glacier mass balance study is concerned with changes in glacier mass through time, and especially the changes from year to year (Ahlmann, 1948 Meier, 1962 Anonymous, 1969 0strem & Stanley, 1969 0strem & Brugman, 1991 Paterson, 1994 Kaser et al., 2002). Glacier mass balance forms the vital link between the changing atmospheric environment and glacier dynamics and hydrology. The most obvious present-day connection between glacier mass balance and global change is the rise in global sea...

Solute enhancement in the proglacial zone

Ferences between subglacial and proglacial environments are that the surface of the proglacial zone freezes, thaws and dries on an annual basis, and that it is a deposition site for snow and rain. Further, there may be ingress of atmospheric gases through the dry surface sediment. These processes perturb the composition of groundwaters within the proglacial zone, for example, there is concentration and recycling of salts via evapoconcentration and freeze concentration and oxic and anoxic...

Impacts of the seaice circulation

Except for areas of landfast ice near the coast, the Arctic ice pack is in near constant motion. The mean annual circulation has two major features, a clockwise motion in the Canada Basin known as the Beaufort Gyre, and a motion of ice from the Siberian coast, across the pole and through Fram Strait, known as the Transpolar Drift Stream (Fig. 23.3). Most of the ice that leaves the Arctic on an annual basis exits through the Fram Strait (between Spitzbergen and Greenland). This flux is primarily...

Salinity PPT

Figure 13.3 (a) Observed (solid lines, in parts per thousand) salinity contour map for the Atlantic continental shelf sediments offshore Long Island, NY. (b) Computed salinity contours applying sea-level boundary conditions (20 sea-level cycles about the Pleistocene mean sea-level of 40 m below modern using a period of 100,000yr with an amplitude of 120 m). (d) Computed salinity contour map (dashed lines, ppt) for the Atlantic continental shelf sediments off shore Long Island, NY applying...

Incorporation into models of icemass motion

Incorporation of basal motion explicitly into ice-sheet models generally is achieved by introducing a sliding term across those cells where basal temperature attains the pressure melting point according to Equation (9), using the local basal shear stress but Figure 67.5 Deformation profiles in glacier ice (a) above a basal zone of low traction corresponding to the location of a major melt-season basal channel and (b) above adjacent ice characterized by higher basal traction. (After Willis et...

Table 732 Frequencies and resolutions of the AMSR microwave radiometer onboard the Us Aqua satellite

23.8 22 X 13 36.5 14 X 8 89 6 X 4 often extensive and permanent darkness occurs for many months of the year, they have the potential, therefore, to provide continuous, synoptic observations. Thus passive microwave radiometers (PMRs) provide valuable (and sometimes the only) data over the polar oceans. The first instrument to provide useful data on sea-ice extent was the electrically scanning microwave radiometer (ESMR) launched in 1972, which was later superseded by the special sensor microwave...

Table 731 Characteristics of the ETM channels

7 2.09-2.35 30 Pan 0.52-0.90 15 Because of their relatively high spatial resolution and temporal extent, Landsat data have proved useful in mapping and monitoring changes in the areal extent of glacier cover. A newer generation of visible IR sensor with several important enhancements compared with the ETM+ is the advanced spaceborne thermal emission and reflection radiometer (ASTER). This comprises a set of three radiometers operating onboard the US Terra satellite, launched in December 1999 as...

Icesheet coupling to the Earth system

Isostatic Coupling

An ice sheet is coupled into the Earth system (Fig. 2.1a) across its interfaces with the atmosphere, the ocean and the lithosphere. 1 Ice sheet-atmosphere coupling. The atmospheric state (temperature, moisture content, energy transport) influences an ice sheet through its impact on mass balance and ice temperature. An ice sheet influences the atmosphere through the deflection of atmospheric flow over the ice sheet, which influences the distribution of temperature, pressure and precipitation and...

The imperative of icesheet research

For 2.6Myr, glacial cycles have altered every aspect of the Earth's environment. The rapidity of climate change through regular glacial cycles drove pre-humans into new habitats and is thought to have provoked an evolutionary response that coincided with the earliest evidence of tool-making. Proxy records from the late Quaternary (approximately the past 1Myr) show that in each cycle, deglaciation was far more rapid than the onset of glacial conditions. During the most recent period of...

Summary

The preceding sections suggested that Antarctica's potential to protect us from the hazard of sea-level rise is considerably less than its potential to make the problem much worse. Predicting the future of the great ice sheets is likely to become increasingly important as global climate change is finally accepted at a governmental level. The present state of change in the Antarctic and Greenland ice sheets was succinctly summarized by Rignot & Thomas (2002) 'As measurements become more...

Spatial variability

There has been a tendency to see glacial erosion as a uniform process that can be compared, for example, with fluvial erosion. One of the realizations from the use of remote sensing over the beds of former ice sheets is just how spatially variable glacial erosion is. There are now numerous accounts of surfaces, commonly marked by river valley networks, tors and blockfields, which have survived inundation by an ice sheet without significant modification, apparently as a result of cold-based...

Fnstitut de Recherche pour le Dveloppement UMR Great Ice IRD Paris France

1 Evaporation from the ocean surface into the free atmosphere is a non-equilibrium process. After equilibrium evaporation into a microskin layer above the sea surface the turbulent diffusive transport into the atmosphere is affected by kinetic diffusion. The latter depends strongly on the saturation of the atmospheric planetary boundary layer, that is, principally on temperature and relative humidity. This is the reason for using deuterium excess records from polar ice to reconstruct past...

FDepartment of Geography University of Durham Science Site South Road Durham DH1 3LE UK

Since the concept of drumlin formation by glacifluvial processes was first proposed by Shaw (1983), a large number of papers have been published interpreting a wide range of subglacial landforms in North America as products of subglacial megafloods (e.g. Shaw & Kvill, 1984 Shaw et al., 1989, 2000 Shaw & Gilbert, 1990 Fisher & Shaw, 1992 Rains et al., 1993 Brennand et al., 1995 Sjogren & Rains, 1995 Shaw, 1996, 2002 Munro & Shaw, 1997 Beaney & Hicks, 2000 Beaney & Shaw, 2000...

Drive point

Figure 77.1 Sketch of the borehole tools. Up to three probes can be placed inside the drill rod. More would interfere with the couplings between the 3 m rod sections. After hammering the probes are pulled out by the detachable drive point that acts as anchor. The hammer (shown in extended position) is connected to the drill rod via an adapter. A variable amount of weight is added to increase the active hammering weight. The hammer is accentuated with a composition rope. whether a light rope or...

Basal melting

For ground-based ice-sheet regions, basal melt freeze-on rates are normally in the order of a few millimetres per year and, therefore, in general are neglected in the mass balance budget. An exception is reported by Fahnestock et al. (2001) who derived basal melt rates of up to 15cmyr-1 beneath an ice stream and adjacent areas in northeast Greenland, probably caused by higher than normal geothermal heat flow. On the other hand, for the extended floating glacier tongues in north and northeast...

Runoff

Most measurements of surface melt and runoff have been concentrated in southwest Greenland with a few scattered observations from other regions (Weidick, 1995). The results, obtained by the traditional method of repeated reading of stakes drilled into the ice, have been extended to the entire ablation region of the ice sheet by degree-day or energy-balance modelling (Reeh, 1989 Van de Wal & Oerlemans, 1994). Records of annual melt duration derived from satellite microwave radiometric data...

Environmental controls and glacier behaviour an overview

Glacier behaviour, and therefore the response of glaciers to environmental change, is fundamentally determined by an interdependent combination of climatic regime and the interaction of the glacier with its immediate geological and topographic environment. Climate controls glacier mass balance through its impact on rates, distributions and types of precipitation and ablation. This mass balance regime in turn is the fundamental ratecontrolling process for dynamics, because the rate of input and...

Calving of icebergs

Iceberg calving is the term for the Greenland Ice Sheet mass budget that is still encumbered with the largest uncertainty. Within the past few decades, Satellite Synthetic Aperture Radar (SAR) Interferomery has revolutionized measurement of icesheet flow, providing area distributions of surface velocity which, when combined with ice-radar measurement of calving-front thickness, allows derivation of iceberg calving fluxes. However, until now the new technique has been applied only to north and...

Fractionation physics during evaporation

An important reassessment of the physics of non-equilibrium fractionation has been made in Cappa et al. (2003). Under non-equilibrium conditions molecular diffusion of the different water isotopomers produces greater fractionation of the lighter water molecules and explains the global deuterium excess value of about d +10 o (if only equilibrium processes controlled evaporation, global excess would equal d 0 ). Mathematically this process was first described in Merlivat & Jouzel (1979)...

Fiftyseven

Manifestations of ice microphysical processes at the scale of whole ice sheets Department of Geography, University of California-Berkeley, 507 McCone Hall, Berkeley, CA 94720-4740, USA Ice sheets live and die according to a grand contest between climate and ice flow. Specifically, the configuration and evolution of ice sheets is governed by the competition between net accumulation rate and the divergence of ice flux arising from gravitationally induced flow. Ice microphysical processes strongly...

S

Figure 27.1 Basal melt rates, B, seaward of Antarctic (hollow circle) and Greenland (solid circle) grounding lines, versus thermal forcing, AT, from the ocean, which is the difference between the nearest in situ ocean temperature data and the seawater freezing point at a depth of 0.88 times the maximum grounding line ice thickness. The regression indicates that a 1 C increase in effective ocean temperature increases melt rate by 10myr-1. PIG, Pine Island THW, Thwaites SMI, Smith KOH, Kohler...

Coupled glacier and climate models

Glacier and ice sheet sensitivity experiments such as those described above highlight regions of the world that are most sensitive to expected changes in temperature or precipitation. More realistic, geographically and temporally explicit scenarios are required for quantitative forecasts of glacier and icefield response to climate change. Studies of this type require coupling of glacier and climate models, and have been carried out to assess the transient response of various ice masses to...

Glacier mass balance and the global glacier inventory GLIMS

The two methods discussed above for determining ice-sheet mass balance can be, and have been, used to determine the mass balance, not only of ice sheets, but also glaciers. Airborne laser altimetry was combined, for example, with cartographic maps, derived from aerial stereo photogrammetry from the 1950s, to estimate dh dt over a period as long as 40 yr for some 67 Alaskan glaciers (Arendt et al., 2002). The results suggested a mass wastage much higher than previous estimates, equivalent to...

Chemical weathering mechanisms and sources of solute

High proglacial chemical weathering rates at Finsterwalderbreen can be explained only by the chemical weathering of rock material in the proglacial zone. Increases in Ca2+, Mg2+ and HCO3-signify the importance of limestone and dolomite dissolution in contributing solute to meltwaters. The ultimate source of the SO42- is oxidation of sulphide minerals, although the dissolution Figure 15.2 Temporal variation in glacial bulk meltwater discharge, and active-layer groundwater stage in Wells 1 and 3...

Mc k0exp[T T0Tc HH w10

Where HW is the water depth, H is the ice thickness and T is ice temperature. The parameters k0, T0 and Tc establish calving vigour and the reduction in calving rates with decreasing temperature. The value for T0 is typically set to 273.16K, such that calving rates are maximal for isothermal ice (T 273.16K mc k0HHW) and mc exponentially decreases for colder ice. This crudely mimics the difference in calving rates observed in mid-latitude tidewater environments versus polar environments, where...

Groundwater flow dynamics under past ice sheets and preservation of old glacial groundwater

Numerical modelling shows that groundwater flow velocities and hydraulic heads in northwestern Europe, especially in the relatively shallow aquifers, were significantly higher under ice sheets than they are at present. For an area bordering the Baltic Sea in Germany, Piotrowski (1997b) estimated flow velocities in the upper aquifer under the last ice sheet as about 30 times higher than at present. Furthermore, a reversal of flow direction occurred. At present, the groundwater drains to the...

Enhancement

Figure 57.2 Relations between steady-state ice volume per divide length (i.e. area of cross-sectional profiles), effective viscosity, stress exponent and two specific controls on viscosity (temperature and enhancement). (a) Black diamonds indicate estimated positions for the three modern ice sheets, according to representative profiles EA, East Antarctic-type WA, West Antarctic-type G, Greenland-type. West Antarctic volumes are those above the flotation level (hence sea-level equivalent). (b...

The problem finding mapping and dating Antarctic icemarginal deposits

The Antarctic Ice Sheets are the largest extant ice masses on Earth, and understanding their history is relevant not only to past environmental changes but also to ongoing changes in global climate and sea level. The glacial-geological record in Antarctica provides a means of reconstructing this history, but the unique features of the Antarctic environment present several challenges that do not arise in more temperate latitudes. In addition to the basic fact that the Antarctic continent is...

Acknowledgements

This work was supported by the D partements Sciences Pour l'Ing nieur and Sciences de l'Univers du CNRS. We are very grateful to V. Lipenkov for valuable suggestions during the preparation of the manuscript. attributed to a single deformation mechanism, dislocation creep, deemed independent of grain size and characterized by a stress exponent n of ca. 3. Despite the widespread adoption of the Glen flow law in glacier and ice-sheet mechanics over the past 50 yr, however, numerous laboratory...

Grand challenges

There is a risk of pomposity and arrogance in even contemplating a list of grand challenges. Everyone will have their own list. However, in the belief that it is sometimes useful and humbling to highlight what we do not know, here is my list. 1 The West Antarctic Ice Sheet stands out as a potential threat in that if it approaches a threshold of collapse, it could raise global sea level by 6 m and change the ocean and atmospheric circulation in the Southern Hemisphere. The signs that it has been...

Changes in the Amundsen Sea sector

The shutdown of Ice Stream C is clear evidence that non-linear behaviour is possible in particular glacier basins, but the discovery by Wingham et al. (1998) of surface elevation change in the Amundsen Sea sector of West Antarctica revitalized the debate about a much more serious type of non-linear behaviour that may govern the fate of the West Antarctic Ice Sheet as a whole. Even when the maps of Antarctica were still blank, Weertman (1974) presented a theoretical analysis of the junction...

Ocean influences

A mean vertical profile of temperature and salinity over the Arctic Ocean reveals several features. There is a low salinity surface layer, with temperatures near the salinity-adjusted freezing point. Below this surface layer, extending to about 200-300 m depth, is a rapid increase in salinity. This is attended by an increase in temperature to maximum (and above-freezing) values at around 300-500m depth. Although temperature falls off at greater water depths, from about 400 m downward salinity...

The sources of evidence

Understanding glaciers and their role in the Earth system demands both an understanding of the way in which their properties are organized in the modern time plane, and how they change through time. The time dimension is important because of the long lag times (102-103yr) that may be required for dynamic changes to spread through the system and the possibility that there have been markedly different ice-sheet regimes through time (e.g. Clark, 1994). In understanding the behaviour of glaciers in...

British Antarctic Survey High Cross Madingley Rd Cambridge CB3 0ET UK

Estimating the bed topography and basal slipperiness indirectly through their effect on surface shape and surface velocity is an example of an inverse problem. If we put all available surface measurements into a vector y, denote the basal properties through x, and write the relationship between bed and surface as y f(x) where f is the forward model, the inverse problem is that of determining the conditional probability distribution function (PDF P(x y)) of a system state given the measurement...

Infrared and microwave radiometers

These instruments record the thermally emitted radiation produced by all natural surfaces. This thermal energy is a function of the physical temperature of the surface and a term known as the emissivity, which defines how much of the radiation is emitted at a given wavelength. Emissivity is the converse of the albedo, or Band number Spectral range (mm) Resolution (m) reflectivity of a surface. In the case of microwave radiometers, the emissivity is a function of the properties of the subsurface...

Marine geological and geophysical records on highlatitude margins

Continental margins extend up to hundreds of kilometres from landmasses, which are often mountainous, to continental shelves with water depths typically of a few hundred metres, the outer limit of which is defined by a shelf break usually at about 500 m (Fig. 30.1). Beyond the shelf break, the margin continues into deep water, via a continental slope (of between about 1 and 10 ), to a deep-ocean basin of very low gradient at abyssal depths of several thousand metres. In the deep sea, the outer...

Significance of relict surfaces

Many formerly glaciated regions include some areas dominated by glacial landforms (Fig. 90.1A) and other areas with distinct non-glacial features (Fig. 90.1B & C). In addition to a suite of characteristic non-glacial geomorphological features (e.g. tors, mountains with approximate radial symmetry, convex-concave slopes, and well-developed blockfields and other periglacial features), areas with non-glacial features, termed relict areas, are particularly conspicuous in formerly glaciated areas...

Palaeoice sheet volume and weathering zones of the Long Range Mountains

Felsenmeer Landform Manual Diagram

In eastern Canada, the extent of glaciation is not easily interpreted from a routine application of glacial geomorphology. This is Figure 89.1 Location of the two weathering zone type localities in western Newfoundland of Grant (1977) and the TCN sampling localities (numbers are last three digits of sample IDs in Table 89.1, erratic boulders in italics). Figure 89.1 Location of the two weathering zone type localities in western Newfoundland of Grant (1977) and the TCN sampling localities...

Surface and borehole geophysics

Ice-penetrating radar has made determination of ice thickness seem routine (e.g. Drewry, 1983b). The ability to map isochrons (Whillans, 1976 Vaughan et al., 1999b Nereson et al., 2000) allows calibration of ice-flow models using tracer fields as described below (Clarke & Marshall, 2002), and assessment of basal melting (Fahnestock et al., 2001) and flow irregularities (Jacobel et al., 1996). Radar remains reasonably good at distinguishing frozen from thawed beds (e.g. Bentley et al., 1998...

Recent deuterium excess icecore studies

The Vostok ice-core has provided a great deal of information about environmental changes in the past 420,000yr (Petit et al., 1999). In a SD-S18O diagram, the ice samples are beautifully aligned on a regression straight line with a slope of 7.94. Vimeux et al. (1999, 2001) have interpreted Vostok deuterium excess variations as depending on fluctuations of the temperature of the oceanic moisture source only, by using a relationship between relative humidity of the air and sea-surface...

Three representative profiles

The GIS profile used here leads westward down-gradient. from the ice divide at Summit (Ohmura & Reeh, 1991). The b used in Equation (16) is 0.23 myr-1 at the divide, increases to a pronounced orographic high on the flank, and then decreases sharply to ca. -6.5myr-1 at the terminus. This melt rate was chosen to ensure zero net balance along the profile. Given an n value, adjustment of one parameter (S(G)) optimizes the model. The EAIS profile used here is that directly inland from Mirny...

William George Adam

School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire ST5 5BG, UK Many interpretations of glacial sediments to reconstruct the basal ice layers of former glaciers have focused upon melt-out tills and glacigenic sediment flows, relying on the preservation of diagnostic glacially derived structures (e.g. Lawson, 1979b Ham & Mickelson, 1994). This approach can be strengthened if the interpretation did not rely solely upon the preservation of diagnostic glacial...

Interaction of the southern LIS and North Atlantic Ocean oscillations of the Mississippi Hudson valley routings

North Direction Schematic

Switches in runoff routing direction, early in deglaciation, between south to the Gulf of Mexico via the Mississippi River Figure 28.7 Schematic diagram of ocean-ice interaction and oscillatory switching of Mississippi runoff to and from Hudson River Valley (after Clark et al., 2001). See text for explanation. Figure 28.7 Schematic diagram of ocean-ice interaction and oscillatory switching of Mississippi runoff to and from Hudson River Valley (after Clark et al., 2001). See text for...

Flowline D

Figure 71.3 Last Glacial Maximum (22.1 ka) and modern ice-sheet reconstructions with isotherms and basal melting indicated for flowlines C (with grounding-line forcing) and D (without grounding-line forcing). (Based on fig. 2 in Parizek et al., 2002, 2003.) In an attempt to reconcile localized basal-freezing tendencies amidst ongoing fast-glacier flow, Parizek et al. (2002, 2003) conducted numerical studies of the basal heat budget. Using a two-dimensional (vertical and along-flow)...

Creep of finegrained ice

The rheological behaviour of materials can be expressed in a general flow law of the form where A is a material-dependent parameter, d is grain size, p is the grain-size exponent, s is differential stress, Q is the activation energy for creep, R is the gas constant and T is absolute temperature. Ambient-pressure experiments on ice samples with uniform grain sizes of 3 lm to 0.2 mm (hereafter referred to as 'finegrained') unequivocally reveal the existence of three creep regimes, shown...

Relict landscapes

African Geophysical Images

The existence of well-preserved relict landscapes with early Weichselian eskers, frost shattered bedrock and the absence of erosional and depositional forms reflecting the flow of the late Weichselian ice sheet have been used by Kleman & H tterstrand (1999) to map areas where the late Weichselian ice sheet was frozen to its bed and where there was therefore no sliding and little or no erosion (Plate 2.1c see also Stroeven et al., this volume, Chapter 90). The fact that erosion can occur...

Figure 766 Drag spool a during insertion and b in operation

Known depth into the substrate, a multi-turn potentiometer, which is connected to a spool and housed within a protective case near the base of the borehole, and a (non-stretchable) cord linking the two (Fig. 76.6). The theory behind the instrument is that the anchor remains in place within the sediment and, as the base of the borehole slides over that sediment layer, the cord is spooled out, turning the potentiometer (Fig. 76.6b). The resistance of the potentiometer is then recorded by a...

Glacial debris release and moraine deposition

Exposure of debris-rich basal ice in many Canadian High Arctic subpolar glaciers during snout downwasting results in the formation of controlled moraine (Fig. 19.2). Preservation potential of these moraines is low, however, owing to sediment redistribution during melt-out. Hummocky till veneers interspersed with glacifluvial outwash occur on valley floors where piedmont glaciers have receded onto surrounding uplands, leaving buried glacier ice at lower elevations. Where debris accumulates by...

Influence of ocean warming on glaciers and ice streams

Thinning of floating ice shelves with resulting unpinning and reduced buttressing of continental ice and grounding line retreat is potentially the largest contributor to sea-level change (Weertman, 1976 Thomas, 1979b van der Veen, 1986). Ice-shelf thinning could occur from enhanced melting at the underside of ice shelves, which could result from changes in properties and circulation of the ocean caused by climate change (Jacobs et al., precede Heinrich events (Darby et al., 2002). Although very...

Continuing Holocene retreat in West Antarctica

There are several methods available that allow us to determine the past configuration of ice sheets these are primarily marine geophysical and geomorphological techniques, but one relatively new technique is substantially improving our understanding of the history of West Antarctica and is worthy of special mention. Using isotopic analysis, it is now possible to determine how long rocks have been exposed to cosmic radiation. When this technique is applied to glacial erratics deposited on the...

Urs H Fischer and Bryn P Hubbardf

Despite the difficulty of making observations at the base of glaciers, numerous studies of processes and conditions at the ice-bed interface have been performed. Direct observations of basal sliding have been carried out in deep, marginal crevasses (Carol, 1947), in natural subglacial cavities (Vivian & Bocquet, 1973 McKenzie & Peterson, 1975 Hubbard, 2002) and in tunnels excavated in the marginal regions of glaciers (Haefeli, 1951 McCall, 1952 Kamb & LaChapelle, 1964 Fitzsimons et...

Subglacial groundwater in past and modern environments

As ice sheets grow and expand over permeable rocks, groundwa-ter flow evolves from a subaerial, precipitation-fed system con- Figure 9.2 Modelled groundwater flow pattern under the margin of the Weichselian ice sheet at its maximum extent at the Main Stationary Line in Denmark (Bovbjerg). Large glaciotectonic folding was facilitated by high porewater pressure in the low-transmissivity bed, partly due to thin aquifers wedging out in the direction of groundwater flow. Note that the transition...

Lggecnrs Bp96 38402 Saint Martin dHeres Cedex France

The Russian station of Vostok was established in 1957 during the International Geophysical Year at the south geomagnetic pole by the Soviet Antarctic Expeditions. The site (78 28'S, 106 48'E) is 1500 km from the ocean, at an altitude of 3488 m a.s.l. with a continental climate and a mean annual temperature of -55 C. The station overlies the southern end of a giant subglacial lake, Lake Vostok. The total ice thickness is 3750 m, and the snow accumulation rate is only 2.2 cm water equivalent per...

Fiftytwo

Average glacial conditions and the landscape of Snowdonia Department of Geography, University of Wales Swansea, Swansea, The Snowdonian mountains of North Wales hold a special place in the history of glacial geomorphology. It was here that Darwin (1842) was convinced of the former existence of glaciers and of their role in shaping the landscape. In the 19th century, it was the battleground of the 'glacialists' and 'diluvialists', with evidence such as the high-level shelly drift of Moel Tryfan,...

The Great Lakes drainage basin

Rhizobitoxine Pathway

After 16.5 ka (19,700 cal. yr), the southern LIS margin receded into the basins of the southern Great Lakes (Erie Interstade) (Fig. 28.4a & b) (Barnett, 1992). For several hundred years the Ontario-Erie and Huron lobes of the LIS retreated enough to switch 0.038 Sv of drainage from the Gulf of Mexico to the North Atlantic Ocean via the Mohawk and Hudson valleys (Licciardi et al., 1999 Lewis et al., 1994) (Figs 28.2 & 28.4b, outlets C and D). (1 Sv 106m3 s-1, or about the present combined...

Controls on North American runoff magnitude and routing

Laurentide Ice Sheet

Runoff from the melting Laurentide Ice Sheet (LIS) and precipitation, plus abrupt releases of stored water in proglacial lakes along the southern margin of the LIS, discharged at different times to the Gulf of Mexico, North Atlantic Ocean, western Arctic Ocean and finally to Hudson Bay. A primary control on the variability in runoff routing stems from the changing configuration of hydrological catchments and drainage basins during deglaciation, which developed by the combination of location of...

Figure 651 Ice composition structure and deformation at the base of Suess Glacier in the Taylor Valley Antarctica

Boundinage Structure Photo

Fitzsimons, 1996 Fitzsimons et al., 1999 Lorrain et al., 1999 Sleewaegen et al., 2003). Holdsworth & Bull (1970) demonstrated that the effective bed of Meserve Glacier (basal temperature 18 C) occurred along the tops of boulders that protruded from the glacier bed into the basal ice. Holdsworth & Bull recorded a debris-rich amber basal ice layer up to 0.6 m thick and demonstrated that salts from the glacier substrate and or the amber ice extended up to 6 m above the glacier base. These...

Icefields and outlet glaciers in Patagonia

Two large ice-covered regions occur in Patagonia. The smaller one is called Hielo Patag nico Norte (Northern Patagonia Icefield NPI) and is about 100km in length and 50km wide, located around 47 S (Fig. 46.1). The larger one is called Hielo Patag nico Sur (Southern Patagonia Icefield SPI), which extends for about 350km from 48 20' to 51 30'S along 73 30'W (Fig. 46.2). The total surface areas of the NPI and the SPI were first estimated as 4400 km2 and 13,500km2 (Lliboutry, 1956), and were...

Georg Kaser

Tropical Glaciology Group, Institute of Geography, Innrain 52, 6020 Innsbruck, Austria A glacier forms when the accumulation of ice exceeds its loss over a time span longer than a few years. The appropriate climatic conditions are driven by the general regional free atmosphere conditions but are also affected by the local topography (e.g. Oerlemans, 2001). A glacier's extent is determined not only by climate glacier-bed conditions also influence the glacier's geometry. Whereas in the highest...

The Siple Dome model

As it is the site of a recent deep-drilling project by the United States Antarctic Program, Pettit (2003) uses available ice-core data and deformation measurements to solve an inverse problem for flow-law parameters that best describe the flow at Siple Dome utilizing an ice-flow model developed by H.P. Jacobson and T. Thorsteinsson. I focus on four flow-law parameters the crossover stress (k), which I assume is spatially constant, and a three-layer isotropic...

Risk Involve In Glacimarine Environment

Since the early 1970s there has been a dramatic increase in the scope and sophistication of glacial sedimentology, to the extent that the discipline of today bears little resemblance to that of 30 yr ago. The intervening period has seen the introduction of a wide range of observational and analytical techniques which allow much more detailed characterization ofglacigenic sediments than was hitherto possible. Moreover, the same period has witnessed a deep shift in outlook among glacial...

Fabric evolution model

Fabric development and macroscopic deformation are studied here by examining the effects ofnearest-neighbour interaction (NNI) among crystals and dynamic recrystallization (Thorsteinsson, 2002). The 'strength' of grain interaction can vary from no interaction (no-NNI), with homogeneous stress (Sachs, 1928), to 'strong' interaction (full-NNI), with significant stress redistribution. Increasing the NNI leads to a more homogeneous strain of all the crystals. There are three dynamic...

Fact

Benn and Evans argue that the basis for the interpretation of the Livingstone Lake drumlins was the form and the presence of sorted sediment in the drumlins. This is a simplification the interpretation was based on the form of drumlins, the style, not the presence, of sediment, clast lithology and rounding, landform association and landform sequence. They also write that the meltwater hypothesis does not predict any systematic difference in the morphology of cavity fill and erosional drumlins....

Weathering rate constants

Mineral weathering rate constants, r, depend on temperature and on mineral surface age. I use expressions for r(t) for major silicate minerals (Table 16.1), and the carbonate (calcite) weathering rate constant, from Morse & Arvidson (2002), is kept constant in time. The rate constants are adjusted from laboratory temperatures (20 C) to T 0 C with the Arrhenius relationship where r is the rate at temperature T (in kelvin), r0 is the rate at temperature T0, Ea is the activation energy of the...

The Lake Agassiz basin

During the first six millennia after the LGM, glacial meltwater and precipitation runoff west of the Michigan basin passed without interruption down the Mississippi River Valley, as the LIS margin retreated toward the northern limit of the Gulf of Mexico watershed. By 11.7ka (13,600cal.yr), the margin had retreated north of the continental divide, and had begun to impound water in proglacial lakes which drained south over the divide (Fig. 28.5a). Continued retreat of the ice margin expanded the...

British Geological Survey West Mains Road Edinburgh EH9 3LA UK

Since the advent of satellite imagery, geomorphologists have used remotely sensed images to gain a better understanding of large-scale landform assemblages. The main benefits of using satellite imagery are clear the large field of view and the range of display scales, both allowing a higher speed of coverage. Many features undetectable on aerial photographs at large scales become readily apparent on LANDSAT images when viewed at a scale of 1 100,000 or more. Unfortunately, few studies use both...

Lake Agassiz ice retreat differential rebound and climatic feedback effects oscillations of St Lawrence Mackenzie and

In the later part of deglaciation of middle North America, after 11.7ka (13,600cal.yr), the retreat of ice under the influence of relatively high summer insolation led to the formation of proglacial Lake Agassiz. The lake, which was impounded by the retreating ice margin on its northern side, initially overflowed the continental divide to the south. During its lifespan, Lake Agassiz enlarged significantly and varied its overflow among southern, eastern and northwestern outlets, as described...

Ploughmeter and dragometer

The ploughmeter (Fig. 76.4) is described in its current form in some detail by Fischer & Clarke (1994) who developed an earlier concept by Humphrey et al. (1993) for use at Trapridge Glacier. The core of the instrument is a ca. 1.5 m long and ca. 20 mm diameter steel rod, the lower end of which is machined into a conical tip for ease of insertion into the subglacial sediment. The rod is sheathed in a clear vinyl tube (internal diameter ca. 25 mm) beneath which strain gauges are bonded by...

Rapid response to contemporary climate change

It can be argued that the majority of the Antarctic Ice Sheet may be uniquely insensitive to small changes in atmospheric climate change. This is because it is so large that the time-scale of the dynamic response is measured in 10 to hundreds of thousands of iecw 90 w 0 so'e we iecw 90 w 0 so'e we Figure 42.4 Long-term (> 30-yr) trends in mean annual temperature measured at meteorological stations around Antarctica. Note the absence of trend data from the sector 70 W to 170 E. (Reproduced...

Geomorphological expression of glacial erosion or lack thereof

The years following World War II saw earth scientists exploring a wide range of glacier environments from Antarctica to mountain glaciers and ice caps lying at the Equator. This geographical coverage combined with recruitment into the new field of 'glaciol-ogy' of physicists and mathematicians led to the development of models of temperature conditions at the bed of glaciers and the large ice sheets. Sugden (1977, 1978) wrote two seminal papers that first developed an estimate for the...

Other dating methods

Another approach to the dating of ice cores is the use of radioactive decay methods, but their usefulness is limited by factors such as the half-life, the low concentration of trace substances and gases in the ice as well as complexities concerning sampling and time resolution. The reader is referred to the literature, for example, the review paper by Stauffer et al. (1989). Such methods can, however, serve as a rough verification of the model or seasonal chronologies, or can be used where...

Subglacial water

Whether fast ice streaming is accommodated by hard-bed sliding or till deformation, at the most basic level it is enabled by the presence of subglacial water at pressures close to the overburden pressure (e.g. Engelhardt & Kamb, 1997 Engelhardt et al., 1990b Kamb, 1991, 2001). Theoretical calculations of basal melting freezing rates indicate that, at least in the Siple Coast region, basal melting predominates inland, particularly beneath ice-stream tributaries, where it takes place at rates...

Basal ice deformation

Above And Below Glacier

Examination of deformation processes at the base of glaciers is beset by numerous problems, which include limited accessibility, structural complexity and spatial variability in physical properties and temporal variability of deformation processes. Access to subglacial locations is a significant problem because deformation of basal ice and subglacial sediment takes place at the ice- substrate interface beneath a substantial thickness of ice, which makes direct observation of deformation...

Polar Science Center Applied Physics Laboratory University of Washington Seattle USA

The Northeast Greenland Ice Stream (NEGIS) provides a good illustration of the utility of interferometric synthetic aperture radar (InSAR) for studying ice dynamics and ice-sheet mass balance. This 700-km-long ice stream was discovered only in the mid-1990s when its presence was detected through the analysis of features visible in SAR imagery (Fahnestock et al., 1993). Soon after velocity on a central portion of this ice stream was mapped using InSAR (Kwok & Fahnestock, 1996). This was...

Glacierclimate relationships Little Ice Age LIA scale

'The term Little Ice Age relates to the behaviour of the glaciers not directly to climate' (Grove, 2001, p. 76 after Luckman). What was once a well accepted, if poorly understood, interval of Earth history is now in debate, as is its companion, the Medieval Warm Period (MWP) (Bradley & Jones, 1993 Hughes & Diaz, 1994 Broecker, 2001). Instrumental data for climatic variables do not exist prior to the 17th century, therefore the atmospheric and ocean climates (Figs 21.1 & 21.2) have to...

Chris D Clark Sarah L Greenwood and David J A Evansf

*Department of Geography, University of Sheffield, Sheffield S10 2TN, UK fDepartment of Geography, Durham University, South Road, Durham DH1 3LE, UK Reconstructing the extent, flow geometry and topography of former ice sheets has recently become more than an academic exercise because of the increasing perception of the importance of the cryosphere in climate change in the earth-ocean-atmosphere system. Of particular note is the discovery that punctuated delivery of freshwater from ice sheets...

Viscous behaviour of ice at low stresses application to polar ice sheets

For conditions prevailing in ice sheets (equivalent stress lower than 0.2MPa), the stress exponent is slightly lower than 2, a value close to that found in isolated single crystals (Fig. 59.1). This result is supported by densification measurements of bubbly ice at Vostok (Lipenkov etal., 1997). The high difference in strain rate between crystals oriented for basal slip and isotropic ice (Fig. 59.1) cannot be explained by a geometric effect related to the random orientation of grains. As at...

Centre for Polar Observation and Modelling School of Geographical Sciences University of Bristol Bristol BS8 1SS UK

In this case study we will illustrate the range of models available to study terrestrial ice masses by concentrating on the study of the ice streams of Antarctica. Ice streams are the focus of a great deal of contemporary research because they discharge the majority (more than 90 ) of the ice leaving Antarctica, and their dynamics are therefore likely to affect the volume of ice stored in the ice sheet and, hence, global sea levels. Ice-flow models can best be classified according to the...

Deuterium excess in ice formed by water freezing

Heavy isotopic water molecules are preferentially incorporated into the growing ice so that the solid is enriched in deuterium and oxygen 18 compared to the water. Equilibrium fractionation always occurs at the ice-water interface but the observed fractionation between ice and bulk water can be lower, depending on the isotopic concentration in the water at the interface. Souchez & Jouzel (1984) have demonstrated that, by partial freezing of an open or a closed system, samples of ice plot in...

Glaciers and their coupling with hydraulic and sedimentary processes2

2 Keynote introduction Glaciers and their coupling with hydraulic and sedimentary processes 3 Geoffrey S. Boulton 3 Haut Glacier d'Arolla, Switzerland hydrological controls on basal sediment evacuation and glacial erosion 23 Darrel A. Swift 4 A glimpse at meltwater effects associated with continental ice sheets 25 John Shaw 5 The erosional origin of hummocky terrain, Alberta, Canada 33 Mandy J. Munro-Stasiuk and Darren Sjogren 6 Tunnel channel character and evolution in central southern Ontario...

Philippe Huybrechts

Alfred-Wegener-Institut f r Polar- und Meeresforschung, Postfach 120161, D-27515 Bremerhaven, Germany and Departement Geografie, Vrije Universiteit Br ssel, Pleinlaan 2, B-1050 Br ssel, Belgium Ice sheets respond dynamically to changes in boundary conditions, such as climate variations, basal thermal conditions, and isostatic adjustments of the underlying bedrock. These cause the ice sheets to evolve towards a new equilibrium. Long response time-scales of up to 104 years are involved,...

Landsystems as modern analogues

The landsystems approach is given more credibility and applicability wherever landscape evolution can be monitored, thereby providing modern analogues for the interpretation of ancient glaciated terrain (e.g. Price, 1969 Gustavson & Boothroyd, 1987 Kruger, 1994 Dyke & Savelle, 2000 Kjsr & Kr ger, 2001 Evans & Twigg, 2002). This type of research on modern glaciers has led to the identification of landform-sediment suites indicative of specific styles of glaciation (e.g. plateau...

The last glacial cycle abrupt glaciological responses to climate

Research on marine cores from the 1970s onward have shown that the isotopic changes in foraminiferal S18O have variations that match those predicted from calculations of the variations in the Earth's orbit (Hays et al., 1976). In particular, peaks in spectral analysis with periodicities of ca. 22, 41 and 100 kyr match variations in obliquity, precession and eccentricity, and it was widely argued that changes in solar insolation, at high northern latitudes, forced changes in the global ice-sheet...

Upscaling from local to global scale

The simplest way to upscale a glaciological characteristic from the local to global scale is to assume that the global value is equal to the average of the available measurements (local values by definition). This seems unsatisfactory for the temperature sensitivity of glaciers because we know that the sensitivity varies greatly between glaciers (see Fig. 83.2), with lower sensitivities in the Arctic (Canada and Svalbard) and in the former Soviet Union and Asia and higher sensitivities in North...