Iceberg Calving Research Articles

Giant icebergs in West Antarctica: Random event or the start of the disintegration of the ice sheets?

Abstract Satellite imagery of the peripheral areas of West Antarctica taken in 1986–1987 revealed the calving of a large number of giant icebergs from the Filchner, Larsen, Thwaites and Ross ice shelves. Their total volume amounted to about 9150 km3, which exceeds the mean annual volume of icebergs discharged from the area by nearly an order of magnitude. The formation of so many giant icebergs suggests a common cause, which we assume to be the significant reduction in the area of sea ice since the early 1970s. The sea ice is in a complex interrelationship with the Ice Sheet; it may serve as a damper to triggering impulses from the ocean, but can also serve as a triggering mechanism itself through impacts or pressure. But in that no signs of general disintegration have been found thus far in the ice shelves or the Antarctic Ice Sheet, the calving of the giant icebergs is considered to be a random process.

Lithostratigraphie et dynamique glaciaires au Wisconsinien, île d'Anticosti, golfe du Saint-Laurent

The Laurentide Ice Sheet deposited three tills on Anticosti Island. The oldest, the Rivière à la Patate Till, was formed by southeastward-flowing ice as determined from till fabrics. The till has an estimated age of 85 000 years BP based on the aminoacid racemization of shell fragments in overlying marine sediments. Thus it is probably Early Wisconsinan in age. The Middle Wisconsinan Rivière Jupiter Till and the Late Wisconsinan Île d'Anticosti Till are the result of the southwest-flowing Laurentide ice. The ice flowed without restriction though without accomplishing deep erosion of the bedrock, as indicated by glaciotectonic structures and till fabrics. However, striated blocks and pebbles in the tills reveal that basal shearing occurred. The ice limit in the Gulf of St. Lawrence from about 36 000 years BP onwards was located along the south coast of the island. This was the result of active calving at the margin of the relatively slow moving ice sheet. During retreat of the ice sheet, an ice cap became isolated on the island. It appears to have remained active in the western part of the island, where it formed the Sainte-Marie Moraine on the south, west, and north coasts, but was less active in the eastern part of the island, where a loose, sandy, but rare till (the Sainte-Marie Till) is the only proof of its activity. Deeper water in the eastern end of the Jacques-Cartier Strait, north of the island, accelerated ice calving and thus probably reduced the ice dynamic in the eastern part of the island. The names of tills used here are proposed as formal nomenclature.

The sublittoral macrofaunal benthos of the Antarctic shelf

A general review of the salient features of the sublittoral macrofaunal benthos of the Antarctic shelf is presented. The need of recognizing a mixed epi-infauna biota, which includes an unusual epi-faunal soft-bottom component, is suggested. This would help the study of the structure of the Antarctic macrobenthos and lend some validity to future quantitative (density and biomass) distribution data. While in large time and space scales the Antarctic environment appears to be rather stable, contributing to a high species diversity, there are sources of disturbances which change the general benthic pattern to a complex mosaic of different successional stages, intergrading with undisturbed communities. Among these sources of disturbance which may be important in structuring benthic communities in Antarctica are anchor ice, ice plucking, ice calving, mud slides, rafted clastic rain, and most important perhaps, iceberg ploughing. The Antarctic benthic realm is unique because of its high taxonomic diversity, widespread endemism, and mostly K-adapted species; biomass is generally high and diverse suspension-feeding communities dominate. There are at present no effective means of establishing extensive protected marine areas or setting aside benthic reserves. SCAR has recognised three marine Sites of Special Scientific Interest, but these have slim chances of being recognized by the Antarctic Treaty itself. While the agreed Measures for the Conservation of Antarctic Fauna and Flora and CCAMLR are not seen as means to develop such extensive marine conservation areas in Antarctica, hope is placed in the Antarctic Minerals Regime which is being negotiated at present. In order to establish a scientifically based scheme for benthic realm conservation, however, both descriptive and experimental research on benthos will have to be greatly expanded around Antarctica.

The Recent Advance of the Ross Ice Shelf Antarctica

AbstractThe seaward edge of the Ross Ice Shelf advanced northward at a minimum average velocity of 0.8 km a–1 between 1962 and 1985. That advance approximated velocities that have been obtained from glaciological data, indicating little recent wastage by iceberg calving. West of long. 178° E., the ice shelf has attained its most northerly position in the past 145 years, and has not experienced a major calving episode for at least 75 years. Since 1841 the ice-front position has advanced and retreated within a zone from about lat. 77° 10’S. (near long. 171° E.) to lat. 78° 40’ S. (near long. 164° W.). The central ice front is now farthest south but has the highest advance rate. Calving may occur at more frequent intervals in that sector, which also overlies the warmest ocean currents that flow into the sub-ice-shelf cavity. Available information on ice-shelf advance, thickness, spreading rate, and surface accumulation indicates a basal melting rate around 3 m a–1 near the ice front. These data and independent estimates imply that basal melting is nearly as large a factor as iceberg calving in maintaining the ice-shelf mass balance. In recent years, the Ross, Ronne, and Filchner Ice Shelves have contributed few icebergs to the Southern Ocean, while projections from a contemporaneous iceberg census are that circumpolar calving alone may exceed accumulation on the ice sheet. Large-scale ice-shelf calving may have preceded historical sightings of increased numbers of icebergs at sea.

The Recent Advance of the Ross Ice Shelf Antarctica

AbstractThe seaward edge of the Ross Ice Shelf advanced northward at a minimum average velocity of 0.8 km a–1between 1962 and 1985. That advance approximated velocities that have been obtained from glaciological data, indicating little recent wastage by iceberg calving. West of long. 178° E., the ice shelf has attained its most northerly position in the past 145 years, and has not experienced a major calving episode for at least 75 years. Since 1841 the ice-front position has advanced and retreated within a zone from about lat. 77° 10’S. (near long. 171° E.) to lat. 78° 40’ S. (near long. 164° W.). The central ice front is now farthest south but has the highest advance rate. Calving may occur at more frequent intervals in that sector, which also overlies the warmest ocean currents that flow into the sub-ice-shelf cavity. Available information on ice-shelf advance, thickness, spreading rate, and surface accumulation indicates a basal melting rate around 3 m a–1near the ice front. These data and independent estimates imply that basal melting is nearly as large a factor as iceberg calving in maintaining the ice-shelf mass balance. In recent years, the Ross, Ronne, and Filchner Ice Shelves have contributed few icebergs to the Southern Ocean, while projections from a contemporaneous iceberg census are that circumpolar calving alone may exceed accumulation on the ice sheet. Large-scale ice-shelf calving may have preceded historical sightings of increased numbers of icebergs at sea.

Mapping Coastal Ice Cliffs and Icebergs From Altimetry Data (Abstract)

In a recent paper, Thomas et.al. (1984) showed how the coast of Antarctica could be mapped using satellite altimetry data. As the satellite approached the continent from the ocean, the Seasat altimeter obtained strong reflections from sea ice, even for a short time after passing over the ice front. Measured ranges are actually oblique distances to the nearest portion of sea ice, yielding a false drop in surface elevation. From the sequence of oblique ranges during a single orbit crossing of the ice cliff, the horizontal position of a segment of the ice cliff is mapped. Currently, the entire Seasat data set is being analyzed to map most of the Antarctic coastline north of 72 °S to an accuracy of ± 0.1 to 1 km, which is a major improvement over existing surveys. The altimeter waveforms corresponding to each range measurement are computer analyzed (“retracked”), using procedures that account for the specular reflections from sea ice and the diffuse reflections from firn. Each waveform analysis, along with the corrected range for data obtained in the vicinity of an ice cliff crossing, is verified or recomputed on an interactive computer, which also computes and maps the position of the ice front. The locations of several tabular icebergs have also been mapped with the same procedures, which can ultimately be used to obtain an estimate of iceberg population density in polar waters, initial results include the mapping of the Larsen ice shelf on the eastern side of the Antarctic Peninsula, showing, for example, the protrusion at approximately 68.5 °S. Estimates of errors in the derived horizontal position are obtained from the analysis of data from repeating orbit tracks. Comparison of these results with results from future altimetry missions will reveal changes in the position of coastal ice cliffs, due to ice movement and/or iceberg calving. Systematic measurements over several years would probably distinguish the effects of iceberg calving, which is intermittent, from those of ice movement, which is continuous.

Mapping Coastal Ice Cliffs and Icebergs From Altimetry Data (Abstract)

In a recent paper, Thomas et.al. (1984) showed how the coast of Antarctica could be mapped using satellite altimetry data. As the satellite approached the continent from the ocean, the Seasat altimeter obtained strong reflections from sea ice, even for a short time after passing over the ice front. Measured ranges are actually oblique distances to the nearest portion of sea ice, yielding a false drop in surface elevation. From the sequence of oblique ranges during a single orbit crossing of the ice cliff, the horizontal position of a segment of the ice cliff is mapped. Currently, the entire Seasat data set is being analyzed to map most of the Antarctic coastline north of 72 °S to an accuracy of ± 0.1 to 1 km, which is a major improvement over existing surveys. The altimeter waveforms corresponding to each range measurement are computer analyzed (“retracked”), using procedures that account for the specular reflections from sea ice and the diffuse reflections from firn. Each waveform analysis, along with the corrected range for data obtained in the vicinity of an ice cliff crossing, is verified or recomputed on an interactive computer, which also computes and maps the position of the ice front. The locations of several tabular icebergs have also been mapped with the same procedures, which can ultimately be used to obtain an estimate of iceberg population density in polar waters, initial results include the mapping of the Larsen ice shelf on the eastern side of the Antarctic Peninsula, showing, for example, the protrusion at approximately 68.5 °S. Estimates of errors in the derived horizontal position are obtained from the analysis of data from repeating orbit tracks. Comparison of these results with results from future altimetry missions will reveal changes in the position of coastal ice cliffs, due to ice movement and/or iceberg calving. Systematic measurements over several years would probably distinguish the effects of iceberg calving, which is intermittent, from those of ice movement, which is continuous.

The Jakobshanvs effect

The Jakobshavns Effect may have been a significant factor in hastening the collapse of palaeo ice sheets with the advent of climatic warming after 18,000 years ago and may precipitate partial collapse of the present‐day Greenland and Antarctic Ice Sheets following CO2‐induced climatic warming in the decades ahead. The Jakobshavns Effect is observed today on Jakobshavns Glacier, which is located at 69°10′N on the west coast of Greenland. The Jakobshavns Effect is a group of positive feedback mechanisms which allow Jakobshavns Glacier to literally pull ice out of the Greenland Ice Sheet at a rate exceeding 7 km/a across a floating terminus 800 m thick and 6 km wide. The pulling power results from an imbalance of horizontal hydrostatic forces in ice and water columns at the grounding line of the floating terminus. Positive feedback mechanisms that sustain the rapid ice discharge rate are ubiquitous surface crevassing, high summer rates of surface melting, extending creep flow, progressive basal uncoupling, progressive lateral uncoupling, and rapid iceberg calving.

Ice calving, carbon dioxide and the control of ice ages

Ice calving, carbon dioxide and the control of ice ages

Ice Shelf Studies off Northern Ellesmere Island, Spring 1983

In spring 1983 work on the ice shelves of northern Ellesmere Island was continued. A total of 55 m of 7.6 cm diameter ice core was obtained from 10 locations. The longest core of 31.79 m is composed of ice-firn and basement ice and can be divided into three distinct strata according to ice salinity. Oscillating strains in Ward Hunt Ice Shelf were measured with a wire strainmeter. It is suggested that the periodic calving of ice from Ward Hunt Ice Shelf might be related to the effects of high frequency oscillation of 35 s to 40 s. Ice conditions along 150 km of coastline continue to change. Continued monitoring of the ice is believed to be necessary in view of the offshore development in the Beaufort Sea.Key words: Ward Hunt Ice Shelf, Milne Ice Shelf, ice cores, strainmeter, coastal ice conditions

Rates and Mechanisms of Iceberg Ablation in the D’Urville Sea, Southern Ocean

AbstractWave action causes ablation in a narrow zone around an iceberg’s waterline, at up to 0.3 m per day, in water of −1°C with waves up to 0.4 m high. Subsequent subaerial calving of ice from iceberg sides takes place up to a similar rate. Submarine melting is an order of magnitude slower than wave action but acts over the largest part of an iceberg. Ablation rates derived theoretically or statistically elsewhere for comparable environmental conditions, are in reasonable agreement with those measured here. Drifting icebergs trail a plume of mixed, slightly cooled and diluted sea-water in their wake.

Rates and Mechanisms of Iceberg Ablation in the D’Urville Sea, Southern Ocean

AbstractWave action causes ablation in a narrow zone around an iceberg’s waterline, at up to 0.3 m per day, in water of −1°C with waves up to 0.4 m high. Subsequent subaerial calving of ice from iceberg sides takes place up to a similar rate. Submarine melting is an order of magnitude slower than wave action but acts over the largest part of an iceberg. Ablation rates derived theoretically or statistically elsewhere for comparable environmental conditions, are in reasonable agreement with those measured here. Drifting icebergs trail a plume of mixed, slightly cooled and diluted sea-water in their wake.

Iceberg calving and deterioration in Antarctica

Iceberg calving and deterioration in Antarctica

Ice-age simulations with a calving ice-sheet model

Variations of ice-sheet volume during the Quaternary ice ages are simulated using a simple ice-sheet model for the Northern Hemisphere. The basic model predicts ice thickness and bedrock deformation in a north-south cross section, with a prescribed snow-budget distribution shifted uniformly in space to represent the orbital perturbations. An ice calving parameterization crudely representing proglacial lakes or marine incursions can attack the ice whenever the tip drops below sea level. The model produces a large ∼ 100,000-yr response in fair agreement (correlation coefficient up to 0.8) with the δ 18O deep-sea core records. To increase confidence in the results, several of the more uncertain model components are extended or replaced, using an alternative treatment of bedrock deformation, a more realistic ice-shelf model of ice calving, and a generalized parameterization for such features as the North Atlantic deglacial meltwater layer. Much the same ice-age simulations and agreement with the δ 18O records, as with the original model, are still obtained. The model is run with different types of forcing to identify which aspect of the orbital forcing controls the phase of the 100,000-yr cycles. First, the model is shown to give a ∼ 100,000-yr response to nearly any kind of higher-frequency forcing. Although over the last 2-million yrs the model phase is mainly controlled by the precessional modulation due to eccentricity, over just the last 500,000 yr the observed phase can also be simulated with eccentricity held constant. A definite conclusion on the phase control of the real 100,000-yr cycles is prevented by uncertainty in the deep-sea core time scales before ∼600,000 yr B.P. The model is adapted to represent West Antarctica, and yields unforced internal oscillations with periods of about 50,000 yr.

Submarine flow tills at Victoria, British Columbia: Reply

during winter to maintain the same average position over a year. Perhaps these cones originated by slumps on the foreslope of subaquatic outwash fans similar to those postulated by Aario (1972) and Rust and Romanelli (1975) for a glacimarine setting. The small proportion of traction current deposits may be due to subglacial streams not having a sufficiently high sediment concentration to maintain an underflow away from the efflux. Occasionally the streams were sufficiently dense to deposit outwash sand and gravel in the foreslope area. The gravity flows may have incorporated the stream gravel, sand, and mud as well as melt-out debris from englacial and basal debris layers. Mixing of these sources during liquefaction perhaps induced by iceberg calving (Powell 1980; p. 70) may produce poorly sorted sediment flows. Thick accumulation by supraglacial melt out from debris layers in a tidewater glacier may best occur where the glacier has almost retreated from the sea and ablation occurs primarily by surface melting rather than iceberg calving (the situation in facies association 111 of Powell 1981). A similar situation of ice in shallow water under mid-latitude temperature conditions was envisaged by Evenson et al. (1977) to explain stratified Quaternary tills, although their interpretation has been questioned (Gibbard 1980). Here the glacial regime and processes are similar to those of the terrestrial environment. Mudflows and debris flows may occur from the ice surface and retain their integrity whilst flowing down a shallower (though still relatively steep) slope into shallow water. If such deposits are not modified by wave action and remain preserved, then they may indicate proximity to sea level in a similar way to deltaic plains.

Methodology And Current Status Of The Prediction Of The Drastic Retreat Of Columbia Glacier, Alaska (Abstract only)

The US Geological Survey was asked to predict the rate of retreat of the terminus of Columbia Glacier, Alaska, which is a large (1 100 km2), grounded, iceberg-calving glacier, and to estimate the time distribution of the attendant discharge of icebergs. An extensive field program, using 1 September 1977 through 31 August 1978 as the principal year of study obtained ice-surface altitudes and velocities, mass-balance values and thickness changes, and bed topography estimated from radio echo-sounding for Columbia Glacier. These data were subjected to complex one- and two-dimensional adjustment programs to assure consistency with the equations of continuity and glacier flow. A one-dimensional numerical model based on the continuity equation was used to make the initial prediction, issued in June 1980. The continuity equation is applied to the lower 14 km of the glacier to deter mine the ice flux to the terminus, and the speed of iceberg calving is taken to he proportional to the average water depth at the terminus. Instead of calculating the dynamics of glacier flow independently, the model requires that a sequence of longitudinal profiles be supplied. Through the calving relationship and other applications of the continuity equation, the model then determines the times at which the glacier assumes each of the supplied profiles. The effect on the predicted rate of retreat caused by the arbitrary nature of the longitudinal profiles is less than the effect of other uncertainties in the data used. A one-dimensional finite-difference dynamic model using the same calving relation gave similar results to those of the continuity model. A two-dimensional, time-dependent, finite-element computer model was also developed. It describes the dynamics of glacier flow along the centerline of the lower glacier using a calving law that relates calving speed to water discharge and to the height of the ice column unsupported by water buoyancy. The retreat predicted by the continuity model slowly accelerates from the initial observed rate of 45 m a−1 until January 1983 ± 10 months, when the retreat rate increases to about 4 km a−1. At some time between October 1933 and July 1986, the terminus is expected to retreat 9.5 km. An annual iceberg-calving flux of about 10 km3 a−1, which is 6 to 8 times the 1978 flux, is expected to occur in 1984; daily or weekly peaks will be much higher. The two-dimensional dynamic model gives similar results, suggesting that retreat will accelerate in 1983, and that a maximum calving flux will be attained in 1984 (see Fig.1.). Fig. 1. Predicted retreat based on the continuity equation model, and observed retreat to 3 September 1982. In the summer of 1980, calving was much less than that observed in previous years, probably due to low amounts of run-off, the fact that the stream discharged in an area of shallow water, and an unusually positive mass-balance year. Thus, the observed retreat is slower than that predicted. However, on 3 September 1982, the observed retreat was within the bounds of error of the original prediction.

Methodology And Current Status Of The Prediction Of The Drastic Retreat Of Columbia Glacier, Alaska (Abstract only)

The US Geological Survey was asked to predict the rate of retreat of the terminus of Columbia Glacier, Alaska, which is a large (1 100 km2), grounded, iceberg-calving glacier, and to estimate the time distribution of the attendant discharge of icebergs. An extensive field program, using 1 September 1977 through 31 August 1978 as the principal year of study obtained ice-surface altitudes and velocities, mass-balance values and thickness changes, and bed topography estimated from radio echo-sounding for Columbia Glacier. These data were subjected to complex one- and two-dimensional adjustment programs to assure consistency with the equations of continuity and glacier flow.A one-dimensional numerical model based on the continuity equation was used to make the initial prediction, issued in June 1980. The continuity equation is applied to the lower 14 km of the glacier to deter mine the ice flux to the terminus, and the speed of iceberg calving is taken to he proportional to the average water depth at the terminus. Instead of calculating the dynamics of glacier flow independently, the model requires that a sequence of longitudinal profiles be supplied. Through the calving relationship and other applications of the continuity equation, the model then determines the times at which the glacier assumes each of the supplied profiles. The effect on the predicted rate of retreat caused by the arbitrary nature of the longitudinal profiles is less than the effect of other uncertainties in the data used. A one-dimensional finite-difference dynamic model using the same calving relation gave similar results to those of the continuity model.A two-dimensional, time-dependent, finite-element computer model was also developed. It describes the dynamics of glacier flow along the centerline of the lower glacier using a calving law that relates calving speed to water discharge and to the height of the ice column unsupported by water buoyancy.The retreat predicted by the continuity model slowly accelerates from the initial observed rate of 45 m a−1 until January 1983 ± 10 months, when the retreat rate increases to about 4 km a−1. At some time between October 1933 and July 1986, the terminus is expected to retreat 9.5 km. An annual iceberg-calving flux of about 10 km3 a−1, which is 6 to 8 times the 1978 flux, is expected to occur in 1984; daily or weekly peaks will be much higher. The two-dimensional dynamic model gives similar results, suggesting that retreat will accelerate in 1983, and that a maximum calving flux will be attained in 1984 (see Fig.1.). Fig. 1.Predicted retreat based on the continuity equation model, and observed retreat to 3 September 1982. In the summer of 1980, calving was much less than that observed in previous years, probably due to low amounts of run-off, the fact that the stream discharged in an area of shallow water, and an unusually positive mass-balance year. Thus, the observed retreat is slower than that predicted. However, on 3 September 1982, the observed retreat was within the bounds of error of the original prediction.

Finite Element Analysis of Calving From Ice Fronts

The Antarctic ice sheet has almost no net annual ablation on its surface, so most mass losses are by iceberg calving along its perimeter, which may be either grounded in shallow water or floating in deep water. An ice cliff forms along the perimeter in both cases. Wave action undercuts ice margins in the tide-water zone along beaches, and causes coastal calving if the rate of undercutting compares with the forward ice velocity. If the ice velocity is sufficiently greater, the ice sheet advances into deeper water and becomes a float at depths of 200 to 300 m (Robin 1979). A floating ice shelf then forms and icebergs calve along the ice front. Iceberg calving along this ice front may be due to several causes (Holdsworth 1977,Robin 1979). Since iceberg calving, either from ice shelves or in the tidewater zone of beaches between ice shelves, is the principal ablation mechanism of the Antarctic ice sheet, it is important to understand calving dynamics quantitatively. This paper presents the results of a finite-element examination of calving along floating margins of the ice sheet.

Finite Element Analysis of Calving From Ice Fronts

The Antarctic ice sheet has almost no net annual ablation on its surface, so most mass losses are by iceberg calving along its perimeter, which may be either grounded in shallow water or floating in deep water. An ice cliff forms along the perimeter in both cases. Wave action undercuts ice margins in the tide-water zone along beaches, and causes coastal calving if the rate of undercutting compares with the forward ice velocity. If the ice velocity is sufficiently greater, the ice sheet advances into deeper water and becomes a float at depths of 200 to 300 m (Robin 1979). A floating ice shelf then forms and icebergs calve along the ice front. Iceberg calving along this ice front may be due to several causes (Holdsworth 1977,Robin 1979). Since iceberg calving, either from ice shelves or in the tidewater zone of beaches between ice shelves, is the principal ablation mechanism of the Antarctic ice sheet, it is important to understand calving dynamics quantitatively. This paper presents the results of a finite-element examination of calving along floating margins of the ice sheet.

A Model for Sedimentation by Tidewater Glaciers

Sampling of sediment from the fjord floor in front of tidewater glaciers in Glacier Bay, Alaska, has provided information about processes in this restricted glacimarine (Dreimanis 1979) setting. Sediment sampling, in conjunction with oceanographic and glacial dynamics data, has also enabled the discrimination of sediment types and their facies associations. Deposits are strongly controlled by: sea-water characteristics, position and sediment discharge of melt-water streams, iceberg calving, and rate of glacierfront retreat.Five distinct facies associations have been found to reflect glacier-fjord regimes. The facies associations and ice-fjord conditions responsible for them form the basis for constructing a preliminary model for glacimarine sedimentation by tidewater glaciers. The model can be used to predict (i) rapid retreat of an actively calving ice front, (ii) slow retreat or stabilization of a calving ice front at a channel constriction, (iii) stabilization of a melting (very rarely calving) ice front when the glacier base is near tidewater elevation, and (iv) large outwash delta progradation into a fjord when the ice front retreats onto land. This model can be used to interpret facies associations found in a stratigraphic record.