This review of the idea of using icebergs as a source of fresh water starts with a historical survey covering the period up to April 1980 and stresses how the approach to the subject has changed with time. Both the progress that has been made and the problems that have either just surfaced or never been adequately addressed are discussed. It is concluded that successful tows to Australia, clearly the most easily-reached potential delivery site, are a possibility if icebergs can be demonstrated to retain their structural integrity during tows in high seas and if favorable schemes can be developed for docking and processing. Tows to sites in the northern hemisphere such as Saudi Arabia and California are significantly more difficult and will remain so until an effective and operationally-realistic method is developed for isolating the iceberg from the warm sea-water that will be encountered during part of the tow. Whatever the ultimate resolution of the iceberg-water proposal may prove to be, research stimulated by this idea has already resulted in a major improvement in our knowledge of the life and times of real icebergs in real oceans.

The Norwegian Antarctic Research Expedition 1978-79 landed on 24 tabular icebergs and flew over many others in the South Atlantic and the Weddell Sea between latitudes 54 and 76°S. Data were obtained on surface mass balance, stratigraphy, density, 10 m temperatures, crevassing, distribution, and age. Ice thicknesses were measured by airborne radio echo-sounding.

All icebergs had experienced surface melting. However, on icebergs south of 66°S., the annual surface melting was only a few centimetres of water equivalent. The average surface mass balance was near zero. Typically the 10 m temperature had increased from about -20° C at the time of calving to -10° C. Only icebergs that had moved northwards from the continent into the west wind drift had snow temperatures close to 0° C. Internal temperatures are increased mainly by the refreezing of percolating melt and rain water. This increased the densities of the upper layers by 100 to 150 kg m-3 above those of nearby ice shelves.

All icebergs measured by radio echo-sounding showed variations in thickness of about 20% of the mean thickness. Nearly all had a convex profile across the short axis and were tilted. An average thickness/freeboard curve indicates that icebergs less than 225 m thick will have permeable layers below sea-level. The ratio of freeboard to thickness varied from 0.21 for a 100 m thick berg to 0.14 for a 350 m thick iceberg.

All icebergs showed systematic surface crevassing parallel with their sides, the crevasse intensity decreasing with distance from the edge. Icebergs with their smallest dimension greater than 400 m usually had a central zone with little crevassing. Grounded icebergs showed severe crevassing, and could not thereafter survive long periods in open water. Bottom crevasses were not detected.

During the Norwegian Antarctic Research Expedition 1978–79, temperature measurements of a number of icebergs and the surrounding surface water were made, using an airborne precision radiation thermometer. All icebergs were embedded in cold water-masses with temperatures generally below 0°C and thus the observed temperature anomalies were relatively small, ΔT ≈ 1 deg. Examples of the influence of icebergs on the sea surface temperature including a possible example of upwelling will be shown. The temperature of the snow-covered iceberg surface was almost constant with individual variations ΔT ≈ 0.2 deg. Local minima indicative of snow-covered crevasses were observed.

Measurements of surface strain and vertical heave responses to swell were made on a tabular ice island in Kong Oscars Fjord, east Greenland, in September 1978. At two sites surface strain was measured with a wire strainmeter of 2 m gauge length, and heave was measured with a vertical accelerometer. While the first site was occupied a simultaneous measurement of ambient wave energy was made with a wave buoy. The results show that the ice island flexes and heaves in response to the longest component only of the forcing wave field, at periods above 16 s, and with a mean strain amplitude of the order of 5 × 10−7. The results are compared with theoretical calculations of the response of a thick floating beam. In the light of the theory, the flexural behaviour of tabular icebergs and sea-ice floes is considered and their critical size ranges in relation to sea state are estimated.

During the Norwegian Antarctic Research Expedition 1978–79, direct measurements of oscillations were carried out on 15 icebergs using a tiltmeter with an accuracy of ± 10 μrad. The amplitude of the oscillations varied from zero to about 103 μrad. The zero amplitude indicates that the berg was grounded and this was confirmed by echo-sounding from the ship. The observed oscillation periods ranged from 16 to 50 s. The observed oscillation periods and the calculated values based on the dimensions and mean density of the bergs were compared and the results are discussed. The flexure of the berg was measured with a theodolite and stakes. Relative movements exceeding the accuracy of the system (1 mm over 1 km distance) were not observed.

During the Norwegian Antarctic Research Expedition of 1978–79, a number of experiments were carried out using side-scanning solar techniques for under-water mapping of icebergs, ice fronts, and ice walls, and for studies of active ploughing areas off ice fronts. This paper presents the techniques and some results, together with views on operational and environmental aspects of using side-scanning sonar in the Antarctic. From the sonographs it is possible to measure depths of icebergs and ice fronts, and to estimate the magnitudes of shape anomalies. Vertical profiles of ice fronts show great variations depending on whether they are grounded or floating. Also, the acoustic signatures vary according to the elapsed time since calving.

Calving of floating ice shelves is studied by a viscoelastic finite-element analysis. The fan-shaped breaking-up of glaciers due to forces that cause bending on creeping ice is assumed to be axisymmetric. Bending may be due to geometry of the bcdrock, action of tides and waves, and imbalance (at the ice front) between the stress in the ice and the sea-water pressure.

The bulk and shear moduli of the ice are represented by relaxation functions of the Prony series, which is a discrete relaxation spectrum composed of a constant and a summation of exponential terms. These properties are also functions of temperature, that varies over the thickness of the ice shelf. The temperature distribution across the thickness of the ice is obtained from calculations based on a linear dependence of thermal conductivity on the temperature. Numerical results are presented for various calving mechanisms. A computer code, VISIC1, is developed by modifying a finite-element viscoelastic code, VISICE, for floating ice islands. The buoyancy of the water is taken into account by a Winkler spring model, with the spring force determined from displaced volume. Locations of crack initiation obtained from the analysis are used to predict the iceberg size immediately after calving.

The tendency of icebergs to roll or heel over is well-known, and so the potential hazards and difficulties of towing unstable icebergs may be appreciated. It follows that there is a need for both accurate and approximate techniques for determining the stability of an iceberg.

As an iceberg melts, the resulting change of shape can cause it to list gradually or to become unstable and topple over suddenly. Similarly, when an iceberg breaks up some of the individual pieces may capsize. We have used Zeeman’s analysis of the stability of ships, which is based on catastrophe theory, to examine this problem. We deal only with statical equilibrium; dynamical effects induced by water motion are important for ships, but very large icebergs have correspondingly small oscillations and therefore dynamical aspects are ignored in this first study. The advantage of the catastrophe-theory approach over the conventional stability theory used by naval architects lies in the conceptual clarity that it provides. In particular, it gives a three-dimensional geometrical picture that enables one to see all the possible equilibrium attitudes of a given iceberg, whether they are stable or unstable, whether a stable attitude is dangerously close to an unstable one, and how positions of stable equilibrium can be destroyed as the shape of the iceberg evolves with time.

By making two-dimensional computations we examine the stability of two different shapes of cross-section, rectangles and trapezia, with realistic density distributions. These shapes may list gradually or topple suddenly as a single parameter is changed. For example, we find that a conversion of the vertical sides of a rectangular section into the slightly inward-sloping sides of a trapezium has a comparatively large adverse effect on stability. The main purpose of this work is to suggest how the stability characteristics of any selected iceberg may be investigated systematically.

Recent geophysical and glaciological investigations of the Ross Ice Shelf have revealed many complexities in the ice shelf that can be important factors in iceberg structure. The presence of rift zones, surface and bottom crevasses, corrugations, ridges and troughs, and other features could substantially modify the hydraulics of iceberg towing and lead to disintegration of the berg in the course of transport.

The relationships between the elevation above sea-level and total ice thickness for three ice shelves (Ross, Brunt, and McMurdo) are given; from them, expressions for the thickness/freeboard ratios of tabular icebergs calved from these ice shelves are obtained. The relationships obtained from the measured values of surface elevation and ice thickness are in agreement with models derived assuming hydrostatic equilibrium.

Areas of brine infiltration into the Ross Ice Shelf have been mapped. Examples of radar profiles in these zones are shown. Absorption from the brine layers results in a poor or absent bottom echo. It is probable that little saline ice exists at the bottom of the Ross Ice Shelf front due to a rapid bottom melting near the ice front, and that the thickness of the saline ice at the bottom of icebergs calving from the Ross Ice Shelf is no more than a few meters, if there is any at all.

We have observed many rift zones on the ice shelf by airborne radar techniques, and at one site the bottom and surface topographies of (buried) rift zones have been delineated. These rift zones play an obvious role in iceberg formation and may also affect the dynamics of iceberg transport. Bottom crevasses with different shapes, sizes, and spacings are abundant in ice shelves; probably some are filled with saline ice and others with unfrozen sea-water. Existence of these bottom crevasses could lead to a rapid disintegration of icebergs in the course of transport, as well as increasing the frictional drag at the ice-water boundary.

Radar profiles of the ice-shelf barrier at four sites in flow bands of very different characteristics are shown. In some places rifting upstream from the barrier shows regular spacings, suggesting a periodic calving. Differential bottom melting near the barrier causes the icebergs to have an uneven surface and bottom (i.e. dome-shaped).

Electrical resistivity soundings on the ice shelf can be applied to estimate the temperature-depth function, and from that the basal mass-balance rate. With some modifications, the technique may also be applied to estimating the basal mass-balance rates of tabular icebergs.

This literature review discusses the mean and variable surface-layer circulation of the Southern Ocean. The variable components are equal to or even more energetic than the mean circulation. Therefore circulation charts often do not present the significant currents that exist during specific periods.

The frequencies of both linear and angular oscillations in a vertical plane of a floating iceberg are shown to converge as the horizontal dimensions become relatively larger. For icebergs of thickness of 250 m, the calculated period of about 30 s is supported by actual observations which have been reported. Because swell in the Southern Ocean may extend to such long periods, a critical relationship between iceberg dimensions and ocean wavelengths has been formulated. This relates the conditions under which the length and natural period of an iceberg may, respectively, coincide with the wavelength and wave period of the ocean.

During the Norwegian Antarctic Research Expedition 1978–79, two experiments were carried out to measure flow around icebergs. Drogues were equipped with surface markers constructed to drift with the flow at various levels down to 260 m. They were tracked by a helicopter and a Motorola positioning system. As expected, the surface-layer (0 to 20 m) flow was wind-induced, but even at greater depths a relative motion of a few cm/s between the water and the iceberg was measured. Such measurements are important for the determination of drag on icebergs, and for melting and erosion processes.

Large-scale furrows occurring in unconsolidated Quaternary sediments on the Labrador Shelf are considered to be gouge marks of bottom-dragging icebergs. Side-scan sonograph mosaics from the northern Labrador Shelf were constructed for two bathymetric interbank areas. They reveal that both relict ice bottom gouging and modern iceberg scouring have taken place at water depths greater than 180 m. The recent scours are linear to curvilinear to crater-like in form, with average widths of 30 m at a mean scour depth of 5 m and lengths in excess of 3 km. The dominant scour trend is north-south, reflecting the Labrador Current.

Impedance of icebergs by bottom interaction is primarily a function of the gross iceberg size and shape, sediment encountered by the keel, and prevailing current. For modern scouring, frequencies of detectable impact decrease exponentially with increasing scour depth, and scour depth is inversely proportional to the sediment shear and compressive strengths.

A numerical model is presented for predicting iceberg drift trajectories from known or derived information regarding iceberg characteristics and the environmental forces affecting the motion of an iceberg. The validity of such a model is studied by comparing predicted and observed trajectories of icebergs near Saglek, Labrador, during a storm on 21–22 August. 1972. At this time, iceberg positions (determined by radar), winds, and currents were monitored as part of an oceanographic study, conducted by the Faculty of Engineering and Applied Science, Memorial University of Newfoundland. The comparison between observed and predicted iceberg drift trajectories is good when the characteristics of the iceberg are assumed to be those of a mediumsized non-tabular iceberg. In order to appreciate the effect of wind and current forces on the drift of the iceberg, several trajectories arc plotted in which various environmental forces are excluded. From this study, it is evident that a good prediction of an iceberg drift trajectory is only possible if rather detailed information is available on the current and wind field.

The drift of eight tabular icebergs is discussed. In spite of large differences in the vertical dimension, the various icebergs seem to react in a similar manner to wind effects in areas covered with sea ice. Measurements indicate that it takes between one and five years for an iceberg to move into the westerlies from the coastal areas between about 50°E. and the Antarctic Peninsula. The drift of the icebergs reflects the integrated current effects in the upper 200-300 m, and may thus also give information about the transport of water masses.

Several factors contribute to the natural drift of an iceberg, and among these, currents play an important part on the translation and rotation. Some information exists on surface currents in sub-Antarctic areas, but an iceberg behaves as a current integrator due to its draught and it is assumed to drift under the action of a “mean” current. In order to measure the mean current, five drogued buoys were launched in July–August 1979. These buoys were located by Argos satellite transponders. The drift of the buoys gives the mean current from 0 to 230 m depth in the Southern Ocean. Some corrections must be made on the measured drifting speed of the drogued buoys, due to the influence of the wind on the above-water portion of the buoys.

In order to avoid the risk of icebergs colliding with drilling vessels and installations in the Labrador Sea, it would be useful to predict iceberg drift. Relevant information on fluid dynamics is summarized, followed by a discussion of various drift models. After commenting on the numerical results obtained with these models, a method is proposed for analysing past trajectories of an iceberg in order to determine coefficients necessary for predicting its drift. The theoretical results are then compared with drift and sea-current and wind data obtained in the Labrador Sea. If accurate prediction of iceberg drift is to be achieved, reliable prediction of oceanic factors is just as important as a knowledge of iceberg characteristics. The techniques developed and tested in the Labrador Sea are helpful whether icebergs are considered as a problem or as a desirable resource.