Small Ice Caps Research Articles

Climate Sensitivity and Equilibrium Climate States Of A Two-Dimensional Energy Balance Model

A two-dimensional energy balance model (EBM) with a seasonal cycle and a realistic land–ocean distribution is used to study climate sensitivity and the properties of equilibrium climate states. The land–ocean distribution is represented by the heat capacity of the surface. The horizontal heat flux is parameterized by diffusion. Nonlinearity is introduced into the model by the albedo–temperature feedback. A multi-grid finite difference method is used to solve the model equation. This method shows great advantages compared to other numerical methods. The sensitivity of snow cover to changes in the solar constant is examined. It is found that the climate is more sensitive in summer due to a more effective albedo–temperature feedback. The local annual mean temperature and the amplitude of the seasonal cycle depend on the land–ocean distribution. Because Eurasia has the largest annual cycle of temperature and is the coldest in winter, winter snow appears first in Eurasia as the solar constant is reduced. Wintertime snow appears next in Greenland because of its low annual mean temperature and last in North America. Perennial snow cover appears first in Greenland because of the low annual mean temperature and the small annual cycle, and next appears in North America. Perennial snow in Eurasia appears only when the solar constant is reduced to a very low value, since the Eurasian land mass is too hot in summer for perennial snow cover. The sensitivity of the model climate to changes in the orbital parameters is also investigated and discussed. Small polar ice caps in one-dimensional mean-annual EBMs are unstable to small perturbations. The ice caps either vanish or grow to a stable finite size. This phenomenon, referred to as the small ice-cap instability (SICI), is a consequence of the multiple stable equilibrium states in one-dimensional models. The SICI may be related to glacial–interglacial transitions. However, numerical results with the two-dimensional EBM demonstrate that the existence of the SICI depends on the land–ocean distribution. The SICI exists in the southern hemisphere, but not in the northern hemisphere. This casts doubt on the role of the SICI in northern hemisphere glaciations. Experiments with a one-dimensional seasonal EBM with simplified geography have been made to analyze the two-dimensional results. Mechanisms for the existence of the SICI in seasonal EBMs are discussed.

Holocene Paleoenvironmental Reconstruction From Deep Ground Temperatures, Canadian Arctic Archipelago: A Comparison With Climatic Inferences From The δ18O Record Of Ice Cores

The δ18O record from ice cores serves as a proxy paleoclimatic temperature record, through the association of isotopic ratio to air temperatures at time of precipitation. Climatic change may be preserved also as a signal in ground temperatures, not as a proxy indicator of past climate but as a direct consequence of the effect of past air temperature variations and associated physical processes at the ground surface. In the Canadian Arctic Archipelago, δ18O records are available from the Devon and Agassiz ice caps, and precision ground temperatures to depths of up to 1000 m are available from 40 petroleum exploration wells, about one third of which are suitable for paleoenvironmental reconstruction. There is an opportunity to compare these two methods of looking at the paleoenvironment, and to show how complementary they are to each other. Geothermal analysis is predicated on the fundamental hypothesis that the terrestrial heat flow, which arises largely from the decay of radioactive elements within the crust, does not vary measurably in the upper few km. But at many wells, the heat flow, calculated as the product of the measured temperature gradient and rock thermal conductivity, does vary systematically with depth in the well. While more random variations may be attributed to measurement errors, and corrections may be made for such known effects as local topography, the residual coherent “long wavelength” variation may be ascribed to effects arising from climate change. Can we, then, determine whether a particular temperature history is consistent with the geothermal record, or ideally, invert the geothermal data to reveal a record of past surface temperatures? Attempts with varying success at paleoclimatic reconstruction from ground temperatures have been reported in the literature (e.g. Lane, 1923; Hotchkiss and Ingersoll, 1934; Birch, 1948; Cermak, 1971; Vasseur and others, 1983; Lachenbruch and others, 1986) and from temperature profiles in ice sheets (e.g. Paterson, 1968; Weertman, 1968; Budd and Young, 1982). In this study, standard techniques in geothermics (e.g. Jaeger, 1965) have been used (1) to show the effect of any hypothesized surface paleotemperature model upon subsurface temperatures, or (2) on the hypothesis that the variation in heat flow is attributed to paleoclimatic effects, to derive a surface temperature model at each well that minimizes the variation in a statistical sense. The resolution of the method and limitations in our measured temperature and rock thermal conductivity data restrict the application of the second method to the past few hundred to one thousand years. The paper considers the first approach for the period 1 ka-10 kaB.p. at about a dozen wells and gives an example of the second approach at a well west of the Agassiz Ice Cap. Aproach (1). In studying the Devon Island ice core, Fisher and Koerner (1979) present a detailed record of the mean annual air temperature at the site throughout the Holocene, based on the δ18O record. A simplified time-temperature model of this record is applied to the ground temperature data set for the period 1 ka-10 ka B.P. Although the effect on the ground temperatures is only subtly perceptible, the model has the effect of reducing the apparent climatically-related curvature in the data, as reflected in an improvement in the standard deviation in the calculated heat flow profile by 5% to 30%. Hence, the geothermal record provides quantitative support for Holocene climatic information derived from the ice core record. Approach (2). This inversion technique is analogous to Paterson’s (1968) reconstruction of the surface temperature during the past century from a temperature profile taken in the small Meighen Ice Cap, Arctic Canada. A unique model is not obtained; rather, a small set of possible surface temperature variations consistent with the deeper subsurface temperatures is produced. Such modelling suggests that subsurface temperatures at a well 180 km west of the Agassiz Ice Cap are consistent with ground surface temperatures some 4–6 Κ lower at the well during the Little Ice Age; this is considerably more severe than the mean annual air temperatures projected from the δ18O record at Agassiz. It is possible that the large increase in ground surface temperature at the wellsite since the Little Ice Age may be attributed to some climatically-related phenomena such as increased incidence of snow cover coherent with the changing climate. A well on Devon Island is not deep enough for a comparison to that ice cap. The oxygen isotope data provide a valuable estimate of Holocene climate with which to correct ground temperature data for terrestrial heat flow, or other studies. However, examination of the signal of more recent events suggests that ground temperatures may be considerably modified by associated transient phenomena such as snow cover, vegetation, etc. Hence, one would expect that such a Holo¬cene correction might either understate or overstate the actual experience of the ground surface at a site.

Holocene Paleoenvironmental Reconstruction From Deep Ground Temperatures, Canadian Arctic Archipelago: A Comparison With Climatic Inferences From The δ18O Record Of Ice Cores

The δ18O record from ice cores serves as a proxy paleoclimatic temperature record, through the association of isotopic ratio to air temperatures at time of precipitation. Climatic change may be preserved also as a signal in ground temperatures, not as a proxy indicator of past climate but as a direct consequence of the effect of past air temperature variations and associated physical processes at the ground surface. In the Canadian Arctic Archipelago, δ18O records are available from the Devon and Agassiz ice caps, and precision ground temperatures to depths of up to 1000 m are available from 40 petroleum exploration wells, about one third of which are suitable for paleoenvironmental reconstruction. There is an opportunity to compare these two methods of looking at the paleoenvironment, and to show how complementary they are to each other.Geothermal analysis is predicated on the fundamental hypothesis that the terrestrial heat flow, which arises largely from the decay of radioactive elements within the crust, does not vary measurably in the upper few km. But at many wells, the heat flow, calculated as the product of the measured temperature gradient and rock thermal conductivity, does vary systematically with depth in the well. While more random variations may be attributed to measurement errors, and corrections may be made for such known effects as local topography, the residual coherent “long wavelength” variation may be ascribed to effects arising from climate change.Can we, then, determine whether a particular temperature history is consistent with the geothermal record, or ideally, invert the geothermal data to reveal a record of past surface temperatures? Attempts with varying success at paleoclimatic reconstruction from ground temperatures have been reported in the literature (e.g. Lane, 1923; Hotchkiss and Ingersoll, 1934; Birch, 1948; Cermak, 1971; Vasseur and others, 1983; Lachenbruch and others, 1986) and from temperature profiles in ice sheets (e.g. Paterson, 1968; Weertman, 1968; Budd and Young, 1982).In this study, standard techniques in geothermics (e.g. Jaeger, 1965) have been used (1) to show the effect of any hypothesized surface paleotemperature model upon subsurface temperatures, or (2) on the hypothesis that the variation in heat flow is attributed to paleoclimatic effects, to derive a surface temperature model at each well that minimizes the variation in a statistical sense. The resolution of the method and limitations in our measured temperature and rock thermal conductivity data restrict the application of the second method to the past few hundred to one thousand years. The paper considers the first approach for the period 1 ka-10 kaB.p. at about a dozen wells and gives an example of the second approach at a well west of the Agassiz Ice Cap.Aproach (1). In studying the Devon Island ice core, Fisher and Koerner (1979) present a detailed record of the mean annual air temperature at the site throughout the Holocene, based on the δ18O record. A simplified time-temperature model of this record is applied to the ground temperature data set for the period 1 ka-10 ka B.P. Although the effect on the ground temperatures is only subtly perceptible, the model has the effect of reducing the apparent climatically-related curvature in the data, as reflected in an improvement in the standard deviation in the calculated heat flow profile by 5% to 30%. Hence, the geothermal record provides quantitative support for Holocene climatic information derived from the ice core record.Approach (2). This inversion technique is analogous to Paterson’s (1968) reconstruction of the surface temperature during the past century from a temperature profile taken in the small Meighen Ice Cap, Arctic Canada. A unique model is not obtained; rather, a small set of possible surface temperature variations consistent with the deeper subsurface temperatures is produced. Such modelling suggests that subsurface temperatures at a well 180 km west of the Agassiz Ice Cap are consistent with ground surface temperatures some 4–6 Κ lower at the well during the Little Ice Age; this is considerably more severe than the mean annual air temperatures projected from the δ18O record at Agassiz. It is possible that the large increase in ground surface temperature at the wellsite since the Little Ice Age may be attributed to some climatically-related phenomena such as increased incidence of snow cover coherent with the changing climate. A well on Devon Island is not deep enough for a comparison to that ice cap.The oxygen isotope data provide a valuable estimate of Holocene climate with which to correct ground temperature data for terrestrial heat flow, or other studies. However, examination of the signal of more recent events suggests that ground temperatures may be considerably modified by associated transient phenomena such as snow cover, vegetation, etc. Hence, one would expect that such a Holo¬cene correction might either understate or overstate the actual experience of the ground surface at a site.

Thermal Response of a Small Ice Cap to Climatic Forcing

AbstractTwo-dimensional finite-element calculations of velocity and temperature fields have been applied to the energy balance of a cross-section of Barnes Ice Cap, Baffin Island, Canada. The flow plane currently is cooling near the ice divide and warming near the margin. Long-term simulations show a net warming trend followed by a cooling trend with a steady-state average temperature similar to the present. Sensitivity studies on an idealized version of the flow plane show that the overall temperature responds less than surface-temperature forcing, because a negative feedback in temperature advection is substantially larger than a positive feed-back in strain heating. The response times of the flow plane by itself are somewhat faster but of the same magnitude as response times that would be estimated from one-dimensional modeling. When bedrock-temperature calculations are included, response times increase an order of magnitude, but these do not substantially affect the short-term response.

Thermal Response of a Small Ice Cap to Climatic Forcing

AbstractTwo-dimensional finite-element calculations of velocity and temperature fields have been applied to the energy balance of a cross-section of Barnes Ice Cap, Baffin Island, Canada. The flow plane currently is cooling near the ice divide and warming near the margin. Long-term simulations show a net warming trend followed by a cooling trend with a steady-state average temperature similar to the present. Sensitivity studies on an idealized version of the flow plane show that the overall temperature responds less than surface-temperature forcing, because a negative feedback in temperature advection is substantially larger than a positive feed-back in strain heating. The response times of the flow plane by itself are somewhat faster but of the same magnitude as response times that would be estimated from one-dimensional modeling. When bedrock-temperature calculations are included, response times increase an order of magnitude, but these do not substantially affect the short-term response.

A projection of future sea level

Evidence is reviewed that suggests faster sea-level rise when climate gets warmer. Four processes appear as dominating on a time scale of decades to centuries: melting of mountain glaciers and small ice caps, changes in the mass balance of the large polar ice sheets (Greenland, Antarctica), possible ice-flow instabilities (in particular on the West Antarctic Ice Sheet), and thermal expansion of ocean water.For a given temperature scenario, an attempt is made to estimate the different contributions. The calculation yields a figure of 9.5 cm of sea-level rise since 1850 AD, which is within the uncertainty range of estimates of the ‘observed’ rise.A further 33 cm rise is found as most likely for the year 2050, but the uncertainty is very large (σ = 32 cm). The contribution from melting of land ice is of the same order of magnitude as thermal expansion. The mass-balance effects of the major ice sheets tend to cancel to some extent (increasing accumulation on Antarctica, increasing ablation on Greenland). For the year 2100 a value of 66 cm above the present-day stand is found (σ = 57 cm). The estimates of the standard deviation include uncertainty in the temperature scenario, as presented elsewhere in this volume.

Depositional controls on glacial facies associations in a basinal setting, late proterozoic, amadeus basin, Central Australia

Diamictites, many established as being glacial in origin, are globally distributed in Late Protezoic rocks. Their widespread occurrence is important in that it implies that significant climatic events occurred during the period between 900 and 600 Ma. However, because of the age of the rocks, correlations are poor and it is difficult to establish, in a convincing manner, whether these sediments were deposited synchronously, during a major global ice age, or if each occurrence of diamictite relates to local climatic or tectonic events. Since the biostratigraphy of these rocks is limited and only a small number of radiometric ages are available, an alternative approach to correlation is necessary. The most promising approach currently available appears to be the application of sequence stratigraphy and the careful evaluation of facies associations on a site by site basis before attempting global correlations. Late Proterozoic diamictites occur in a number of intracratonic basins in a broad belt across the ancient Australian craton. Two Late Proterozoic diamictite units, both previously identified as glacial in origin, are exposed in the intracratonic Amadeus basin of central Australia. The Areyonga Formation, the older of the two units, forms the basis of this study. The Areyonga Formation is contained within a major depositional sequence, the Areyonga sequence, the bounds of which were determined by basin dynamics and eustatic sea-level changes induced by an ice age of global dimensions. During deposition of this sequence three major sedimentological systems were in operation. Along the northern margin of the basin glaciation dominated sedimentation. In the south large volumes of sediment were deposited in a shallow-marine setting whilst to the west braided streams supplied sediment to a major coastal plain and delta system. All three systems operated within the same sea-level and basinal constraints but each contributed sediment to the basin independently. The glacial sediments of the Areyonga sequence were deposited from a relatively small ice cap lying between the Amadeus Basin and the Ngalia Basin to the north. Sediments were deposited from two tongues of ice that extended about 100 km into the northeastern corner of the Amadeus Basin. Glacial sedimentation occurred in three stages determined by the initial fall and subsequent rise in eustatic sea level as the ice sheet grew and declined. Initially thick massive basal till units were deposited on an erosion surface intersected by subglacial and ice-marginal channels. They were then followed by thinner till units separated by channel-like sandstone and conglomerate with associated boulder surfaces or concentrations that were deposited by an extensive subglacial drainage network. Finally, the subglacial deposits grade into ice-proximal and ice-distal shallow-marine sediments deposited in part by mass movement. Sedimentation appears to have been terminated by a major sea-level fall. In the Ooraminna sub-basin to the east, rocks, originally thought to have been deposited during a second glaciation, appear to be part of a lowstand wedge formed during a sea-level low following the Areyonga glaciation. A record of the second glaciation probably does not exist in the Amadeus basin. Similarly, diamictites in the Inindia beds and originally correlated with the Areyonga Formation have been shown to belong to the non-glacial lowstand wedge of the following sequence. Preservation of glacial sediments is most likely to occur in a basinal setting where depositional space is being actively created. In the Amadeus basin depositional space was created prior to deposition of the Areyonga Formation by subsidence following crustal extension that occurred approximately 150 m.y. previously. The distribution of sequence boundaries and the succession of facies associations identified in the Areyonga sequence provide the basis for a depositional model for glacial sedimentation during an ice age. To be successful, correlation of Late Proterozoic glacial sediments must be based on an understanding of these facies associations and their bounding depositional surfaces. Associations similar to those found in the Amadeus basin have been documented in other Proterozoic basins suggesting that the facies associations and relationships recorded in the Areyonga sequence may form the basis for a generalized model for basinal sedimentation from an ice age of global significance. If this is so, it should be possible to determine if a sequence containing glacial sediments is part of a global climatic event or simply due to local conditions from a single site evaluation.

The Sensitivity of a Small Icecap to Climatic Fluctuations

The glacial chronology, obtained from proglacial lacustrine sediments, shows that Riukojietna, a small ice cap. disappeared or was small and inactive in the early-mid Holocene. A reactivation of the ice cap occurred around 2000 B.P. Riukojietna has retreated rapidly after a distinct maximum in extent in the beginning of the twentieth century. Measurements yielded negative net balances between 1985 and 1988. Differences in net balance seem to be caused primarily by fluctuating summer balances. Since Riukojietna has a relatively small vertical extent and is relatively low lying compared with cirque glaciers, it is much more sensitive to changes in the climate. Riukojietna is far from being in balance with the existing climate and will, if present trends continue, finally disappear.

The Sensitivity of a Small Icecap to Climatic Fluctuations

The Sensitivity of a Small Icecap to Climatic Fluctuations

Glacier velocities from aerial photographs in North and North-East Greenland

General descriptions of the glaciers of North and North-East Greenland have been given by Koch (1928), Davies & Krinsley (1962) and Weidick (1975). These descriptions, however, provide little in the way of quimtitative data on glacier velocities, although Davies & Krinsley cancluded that a large number af glaciers and small ice caps in North Greenland exhibited stable conditions, with a significant number showing evidence of recent retreat. Comparisons of vertical aerial photographs taken in 1959-63, 1971 and 1978 permit measurements ef glacier velocity to be made on floating ice tongues which have preserved a distinctive surface pattern of meandering streams and crevasses. These show the largest glaciers draining the Inland Ice in North and North-East Greenland to have average velocities ranging from 300 to 900 m/year. This study of vertical aerial photographs has also demonstrated that for floating glacier tongues the position of the glacier terminus is not areliable indicator of advance or retreat. In the fjords of North Greenland semi-permanent sea ice often maintains the integrity of advancing floating glacier fronts for periods of ten to twenty years (Koch, 1928; Weidick, 1975); the break-up of the floating tongue in rare summers when the sea ice melts completely may give the impression of a sudden retreat, but this 'retreat' is unrelated to changes in the mass balance.

Assessment of polar climate change using satellite technology

Results from general circulation models (GCMs) have indicated that a predicted climate warming resulting from an increase in atmospheric carbon dioxide (CO2) will be amplified in the polar regions and that temperature increases in the polar regions will be several times greater than the global average. Some GCMs predict a 4°–5°C average air temperature increase in the Arctic by the middle of the next century. Evidence from the polar regions indicates that a warming in the cryosphere may already be in progress. A 2°–4°C rise in permafrost temperature, measured in northern Alaska, is believed to have occurred during the last 100 years. In addition, many small valley glaciers and ice caps have experienced retreat and appear to have contributed up to 50% to the observed rise (10–15 cm) in sea level during the last century. Other work shows that increased snowfall which can be associated with warmer temperatures has caused thickening of some Alaskan glaciers. Though a decrease in snow and sea ice cover would be a likely consequence of global warming, a sustained decrease in global snow and sea ice extent has not been found from analysis of more than 20 years of image data (1.1‐km pixel resolution) from National Oceanic and Atmospheric Administration meteorological satellites and more than 7 years of scanning multichannel microwave radiometer snow data (30‐km pixel resolution) on the Nimbus 7 satellite. Snow and sea ice are sensitive to atmospheric temperature changes because of their large surface to volume ratio. While measurements of snow and sea ice extent, snow depth, and sea ice concentration are possible using visible, near‐infrared, or microwave sensors on satellites, it is not feasible to measure the mass balance of the ice sheets with these sensors directly. Estimates by glaciologists show that the Greenland Ice Sheet is in approximate equilibrium and that the Antarctic Ice Sheet has a positive mass balance. Satellite radar altimetry (and in the future, laser altimetry) is a promising technique for measuring the surface elevation of ice sheets. Satellite‐borne laser altimetry in conjunction with imagery on ice sheet extent will permit direct measurements of changes in mass balance of the ice sheets through time. The terminus positions and ablation area boundaries of valley glaciers are indicative of glacier mass balance; these can be studied using visible and near‐infrared data from the Landsat satellite series and data from the French Systeme Probatoire d'Observation de la Terre (SPOT) satellite and synthetic aperture radar data. Lake ice freeze‐up and breakup dates are sensitive to regional air temperature and may also be good indicators of climate trends. Monitoring the onset of lake freeze‐up and breakup dates is feasible with radar and visible image data. The very important role of snow and ice in global processes is being highlighted as large‐scale, satellite‐derived geophysical data sets have become available and are beginning to be used as realistic input to GCMs.

Structure and Flow in the Margin of the Law Dome Ice Cap. Antarctica (Abstract)

The internal structure of the Law Dome ice cap is being investigated by studying ice cores obtained from several sites along the summit-Cape Folger line. Profiles of measured physical properties for four of the ice cores from near the margin of the ice cap are presented. A comparison of the profiles shows a gradual increase and then decrease in crystal size, and the development of strong crystal anisotropy in the upper half of the ice thickness. But in the lower part there is a complex multi-layer crystallographic structure, with an interleaving of ice which has markedly different physical properties. The development of the physical properties in the ice cores is discussed in terms of the deformation in the ice cap in the neighbourhood of the bore holes and the movement of the ice over the rough bedrock. The interdependence of the physical properties and the flow within the ice cap and their effect on other proxy records obtained from the ice cores are also explored.The Law Dome is a small ice cap, about 200 km in diameter, adjoining the main Antarctic ice sheet. It is being studied as a model ice cap, using surface surveys and ice-core drilling. It is large enough to have most of the features of larger ice sheets but small enough to be investigated in considerable detail. The four cores were drilled within 10 km of the coast at Cape Folger and lie approximately along a flow line. Each of the cores covers the Holocene and at least the later part of the Last Glacial Maximum. Two of the cores are within 40 m of bedrock and the remaining two, in thinner ice nearer the coast, are within a few metres of bedrock. Physical properties which were measured include: crystal size, texture and orientation; bubble size, orientation and distribution; and visible stratigraphy. The stratigraphy in the upper layers is related mainly to the occurrence of surface melting during the warmer months of the year. Additional supporting information is available from measurements of the physical properties on shallow cores up-stream of the four bore holes, from radio echo-sounding profiles and from other studies on the ice cores. This data is used in the discussion of the velocity field in the ice cap.

Structure and Flow in the Margin of the Law Dome Ice Cap. Antarctica (Abstract)

The internal structure of the Law Dome ice cap is being investigated by studying ice cores obtained from several sites along the summit-Cape Folger line. Profiles of measured physical properties for four of the ice cores from near the margin of the ice cap are presented. A comparison of the profiles shows a gradual increase and then decrease in crystal size, and the development of strong crystal anisotropy in the upper half of the ice thickness. But in the lower part there is a complex multi-layer crystallographic structure, with an interleaving of ice which has markedly different physical properties. The development of the physical properties in the ice cores is discussed in terms of the deformation in the ice cap in the neighbourhood of the bore holes and the movement of the ice over the rough bedrock. The interdependence of the physical properties and the flow within the ice cap and their effect on other proxy records obtained from the ice cores are also explored. The Law Dome is a small ice cap, about 200 km in diameter, adjoining the main Antarctic ice sheet. It is being studied as a model ice cap, using surface surveys and ice-core drilling. It is large enough to have most of the features of larger ice sheets but small enough to be investigated in considerable detail. The four cores were drilled within 10 km of the coast at Cape Folger and lie approximately along a flow line. Each of the cores covers the Holocene and at least the later part of the Last Glacial Maximum. Two of the cores are within 40 m of bedrock and the remaining two, in thinner ice nearer the coast, are within a few metres of bedrock. Physical properties which were measured include: crystal size, texture and orientation; bubble size, orientation and distribution; and visible stratigraphy. The stratigraphy in the upper layers is related mainly to the occurrence of surface melting during the warmer months of the year. Additional supporting information is available from measurements of the physical properties on shallow cores up-stream of the four bore holes, from radio echo-sounding profiles and from other studies on the ice cores. This data is used in the discussion of the velocity field in the ice cap.

Mass Balance of Two High Arctic Plateau Ice Caps

AbstractMass-balance measurements have been renewed on two small ice caps on north-eastern Ellesmere Island. Original stake networks were established in 1972 and 1976. Since then, both ice caps have experienced significant mass losses averaging –70 to –140 kg m−2a−1. They have also decreased in area. The equilibrium line in this area has averaged around 1150 m for the last decade or so. The ice caps are remnants of former climatic conditions and are out of equilibrium with contemporary climate.

Mass Balance of Two High Arctic Plateau Ice Caps

AbstractMass-balance measurements have been renewed on two small ice caps on north-eastern Ellesmere Island. Original stake networks were established in 1972 and 1976. Since then, both ice caps have experienced significant mass losses averaging –70 to –140 kg m−2 a−1. They have also decreased in area. The equilibrium line in this area has averaged around 1150 m for the last decade or so. The ice caps are remnants of former climatic conditions and are out of equilibrium with contemporary climate.

Evidence of a Periodic Ice-Cliff Avalanche on North-West Ellesmere Island, N.W.T., Canadian High Arctic

AbstractEvidence of a recent (1985) ice-cliff avalanche from an outlet lobe of a small plateau ice cap on north-west Ellesmere Island is discussed. Former avalanche events are evidenced by debris lying outside the 1985 avalanche material. Periodic activity seems to be linked to the build-up of melt water in the crevasses of the outlet lobe during the melt season. The exact magnitude and frequency of events are unknown. Some implications to geomorphology and the sedimentology of sub-polar glaciers are discussed.

Evidence of a Periodic Ice-Cliff Avalanche on North-West Ellesmere Island, N.W.T., Canadian High Arctic

AbstractEvidence of a recent (1985) ice-cliff avalanche from an outlet lobe of a small plateau ice cap on north-west Ellesmere Island is discussed. Former avalanche events are evidenced by debris lying outside the 1985 avalanche material. Periodic activity seems to be linked to the build-up of melt water in the crevasses of the outlet lobe during the melt season. The exact magnitude and frequency of events are unknown. Some implications to geomorphology and the sedimentology of sub-polar glaciers are discussed.

Glaciations of the West Coast Range, Tasmania

Geomorphic, stratigraphic, palynologic and 14C evidence indicates that the West Coast Range, Tasmania, was glaciated at least three times during the late Cenozoic. The last or Margaret Glaciation commenced after 30,000 yr B.P., culminated about 19,000 yr B.P., and ended by 10,000 yr B.P. During this period a small ice cap, ca. 250 m thick, and cirque and valley glaciers covered 108 km 2. The glacial deposits show little chemical weathering or erosional dissection. The snow line ranged from 690 to 1000 m with an average of 830 m for the ice cap. Mean temperature was 6.5°C below the present temperature. During the preceding Henty Glaciation a 300- to 400-m-thick ice cap and outlet glaciers exceeded 1000 km 2. The glacial deposits are beyond 14C assay. They are more weathered chemically and more dissected than Margaret age deposits, and the degree suggests a pre-last interglaciation age (> 130,000 yr B.P.). The snow line of the ice cap lay at 740 m, and annual temperature was reduced by 7°C. Ice of the earliest Linda Glaciation slightly exceeded that of the Henty Glaciation but had a similar distribution. The glacial deposits are intensely weathered, have reversed magnetization, and overlie a paleosol containing pollen of Tertiary type. An early Pleistocene or Tertiary age is indicated.

The Small Ice Cap Instability in Diffusive Climate Models

Simple climate models employing diffusive heat transport and ice cap albedo feedback have equilibrium solutions with no stable ice cap smaller than a certain finite size. For the usual parameters used in these models the minimum cap has a radius of about 20 degrees on a great circle. Although it is traditional to remove this peculiar feature by various ad hoc mechanisms, it is of interest because of its relevance to ice age theories. This paper explains why the phenomenon occurs in these models by solving them in a physically appealing way. If an ice-free solution has a thermal minimum and if the minimum temperature is just above the critical value for formation of ice, then the artificial addition of a patch of ice leads to a widespread depression of the temperature below the critical freezing temperature; therefore, a second stable solution will exist whose spatial extent is determined by the range of the influence function of a point sink of heat, due to the albedo shift in the patch. The range of influence is determined by the characteristic length in the problem which in turn is determined by the distance a heat anomaly can be displaced by random walk during the characteristic time scale for radiative relaxation; this length is typically 20–30 degrees on a great circle. Mathematical detail is provided as well as a discussion of why the various mechanisms previously introduced to eliminate the phenomenon work. Finally, a discussion of the relevance of these results to nature is presented.

An analysis of the Permo-Carboniferous glaciation in the marine Kalahari Basin, Southern Africa

The Dwyka Formation, which forms the basal unit of the sedimentary fill in the Kalahari Basin, consists of local reddish basal tillite, an argillaceous sequence of shale, mudstone, siltstone, sandstone, diamictite and carbonate lenses and nodules containing marine fossils, and a well-developedmain tillite. In the Hotazel Valley along the southern margin of the basin an upper tillite is also present. The sequence represents two major ice advances separated by a well-defined interglacial and a minor ice advance confined to the area around the ice-spreading centre. Glacial erosion during maximum glaciation in the late Carboniferous formed a dissected landscape depressed isostatically to below sea level. Ice flow during deglaciation was controlled by the basement topography and upon disintegration of the ice sheet the sea followed the retreating ice inland (Hardap Interglacial). Deposition of lodgement till at the ice grounding line was followed by debris flows, turbidity currents, debris rain and suspension settling leaving sediments typical of an ice retreat sequence. The Tses Glaciation, probably of Early Permian age, followed on the interglacial. A marine ice sheet covered the area and predominantly logdement tills and bedded and laminated diamictons were deposited during grounding line retreat, underside melting of ice shelves and by icebergs respectively. After rapid collapse of the marine ice sheet, small ice caps remained in the mountainous areas and during a temporary ice advance another till horizon was deposited along the southern margin of the basin.