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The Australian National University
Research School of Earth Sciences

Glacial rebound and sea-level change: solutions for ocean-volume fluctuations, ice sheets and mantle rheology

Kurt Lambeck. Tony Purcell, Jason Zhao, Andrea Dutton.

As ice sheets melt or grow, the load on the earth's surface changes and the planet's shape and gravity field is modified. This is seen in a range of geological, geophysical and geodetic observations. An important geological observation is the height and elevation of former shorelines above or below present sea level. Geodetic observations include the radial displacement of the crust or the acceleration of satellites as the gravity field changes. Inversion of such observations provides information on the EarthÕs rheology and on the history of the ice sheets. The rheological results are robust and the main emphasis of current work is on improving models of the ice sheets. This is achieved through a combination of field, laboratory, and numerical modelling. Study areas included in 2005 projects include Scandinavia and Arctic Russia (see below), The Baltic Sea (through a joint project with Shiyong Yu and Bjoern Berglund of Lund University, Sweden), Greenland (through a joint project with Charlotte Sparrenbom of Lund University, Sweden), the Gulf of Mexico (through a joint project with Alex Simms of Rice University, USA), the Mediterranean (through joint projects with Marco Anzidei of INGV, Rome, and Fabrizio Antonioli of ENEA, Rome), and Singapore (through a joint project with Michael Bird, now at St Andrews, Scotland).


The focus of the glacial rebound work in 2005 has focussed on Arctic Eurasia from the time of the penultimate glacial maximum (MIS 6 or the Late Saalian at ~145,000 years ago) up to the present. The aim of this work is to establish constraints on the ice thickness and ice margins for some of the major phases of the last glacial cycle that are independent of glaciological or climate assumptions. The penultimate glacial maximum was one of the largest ice sheets over northern Europe and the Russian arctic, extending from the British Isles to the Taymyr Peninsula. This was followed by the Eemian Interglacial and by a series of alternating stadials and interstadials over Russia and Scandinavia culminating in the last glacial maximum at ~ 20,000 years the end of which the next cycle of glaciation started. The principal outcomes are: the completion of compilations of field evidence for the ice margin locations and shoreline elevations and sea levels across the region; the inversion of this data for ice thickness during the principal glaciations corresponding to the marine isotope stages 6, 5d, 5c and 4; and the palaeo-geographic reconstructions for these periods. During the Late Saalian the ice extended across northern Europe and Russia with a broad dome centred from the Kara Sea to Karelia that reached a maximum thickness of c. 4500 m and ice surface elevation of c. 3500 m above sea level. A secondary dome occurred over Finland with ice thickness and surface elevation of 4000 m and 3000 m respectively (Figure 1). When ice retreat commenced, and before the onset of the warm phase of the Early Eemian, extensive marine flooding occurred from the Atlantic to the Urals and, once the ice retreated from the Urals, to the Taymyr Peninsula. The Baltic Ð White Sea connection is predicted to have closed at about 129 kyr BP although large areas of arctic Russia remained submerged until the end of the Eemian (Figure 1).




Figure 1 (A-E): Palaeogeographical reconstruction for selected epochs for Eurasia from the time of the penultimate glacial maximum to the stadial corresponding to MIS 4. The areas covered by grounded ice are shown by the white translucent areas with ice thickness contours (white lines) at 250 m interval from 0 to 1000 m and at 500 m interval thereafter. The contours of negative and zero sea level change are in red and positive values in yellow (e.g. the 200 m contour represents palaeoshorelines that are now 200 m above sea level). For (A) to (C) the negative contours are at 50 m intervals and the positive contours are at 100 m interval. For (D) and (E) the negative contours are at 25 m intervals and the positive contours are at 50 m interval. The palaeo-shoreline locations are defined by the green-blue boundary and palaeo-topography above coeval sea level is indicated by the green and brown colour gradations at 25, 50, 100, 200 m and higher elevations. Palaeo-water depths are defined by the blue colour gradations at -25, -50, -100, -200 m and deeper depths. The ocean depths and land elevations are with respect to sea level for the specified epoch. Water depths of enclosed bodies are with respect to the sill elevation that defines the enclosed basin.



During the stadials (MIS-5d, 5b, 4) the maximum ice was centred over the Kara-Barents Seas with a thickness not exceeding c. 1200 m. Ice dammed lakes and the elevations of sills are predicted for the major glacial phases and used to test the ice models (Figure 1). For example, large lakes are predicted for west Siberia at the end of the Saalian and during MIS-5d, 5b and 4, with the lake levels, margin locations and outlets depending interalia on ice thickness and isostatic adjustment and comparison with the field evidence then permits further inferences about the ice margins and ice thickness. The results are to appear in Boreas. Subsequently the investigation has been continued from MIS-4 to MIS-2 to include the period of rapid changes in ice cover over Scandinavia and to provide constraints on the European and Russian ice sheets for the complete interval from MIS 6 to the present.


Related to this investigation is the study of sea-level fluctuations in the Mediterranean during the last interglacial (MIS 5e). The Mediterranean lies on the forebulge of the Late Saalian ice sheets and the present elevations of 5e shorelines are interalia a function of the Stage 6 and subsequent ice sheets. The predicted Eemian sea-level signal for these locations is distinctly different from that at sites further from the former ice sheets and the differences are determined by the ice and earth model parameters. The amplitudes of the signals at both sites are determined by these parameters and by the ice volumes during the interglacial and the comparison of the data from the Mediterranean with far-field evidence from Western Australia indicates that land-based ice volumes during the middle and later parts of the Eemian were less than during the present interglacial by as much as 5 m sea-level equivalent (Figure 2).




Figure 2 (A-E): Same as Figure 1 but for the post Eemian period. The rebound contours are the same as in Figure 1D.



Related work in the Mediterranean includes the study of speleothems from submerged caves and dating of molluscan shells to refine the sea level curve for the past and earlier cycles ( see U-series dating of molluscan shells from the Mediterranean ) and further work on the use of Roman-era fish tanks as sea-level indicators (see Anzidei, M., Benini, A., Lambeck, K., Antonioli, F., Esposito, A., Surce, L. 2005. Siti archeologici costieri di etˆ romano come indicitori della variazioni del livello del mare: unÕapplicazione al mare Tirreno (Italia centrale). In Evoluci—n Palaeoambiental de Los Puertos y Fondeaderos Antiguos en el Mediterr‡neo Occidental. L. de Maria and R. Turchetti, Eds, Rubbetino, Rome, pp115-126).


A second focus has been on the stress evolution in the crust during a glacial cycle to answer specific questions about the stability of the crust during and after major glaciations. What is the evolution of the state of stress in the crust during a glacial cycle and how does the crust respond to the superpositioning of these stresses on long-term background stress fields. If these questions can be resolved it becomes possible to estimate the likelihood of fault reactivation during future glacial cycles in areas that may otherwise be appropriate for the long-term storage of nuclear waste. These questions have been investigated for waste repository sites in Sweden, using the past glacial cycle as representative of future cycles and it has been possible to show that fault stability enhancement or reduction is strongly dependent on location relative to the ice sheets and that the glacial-load stress is a factor to be considered in any final decisions on repository site locations.




Lambeck, K., Purcell, A. 2005; Sea-level change in the Mediterranean Sea since the LGM: model predictions for tectonically stable areas. Quaternary Science Reviews, 24, 1969-1988.


Anzidei, M., Benini, A., Lambeck, K., Antonioli, F., Esposito, A., Surce, L. 2005. Siti archeologici costieri di etˆ romano come indicitori della variazioni del livello del mare: unÕapplicazione al mare Tirreno (Italia centrale). In Evoluci—n Palaeoambiental de Los Puertos y Fondeaderos Antiguos en el Mediterr‡neo Occidental. L. de Maria and R. Turchetti, Eds, Rubbetino, Rome, pp115-126.


Lambeck, K. 2005.Glacial load stresses: Can existing faults or other zones of crustal weakness be reactivated during glacial cycles? In Expert Panel Elicitation of Seismicity Following Glaciation in Sweden (Eds S. Hora and M. Jensen). Statens strŒlskyddinstitut rapport 2005:20 pp 85-106. Stockholm, Sweden.


Sparrenbom, C.J. Bennike, O., Bjorck, S., Lambeck, K., 2006. Relative sea-level changes since 15000 cal. Yr BP in the Nanortalik area, southern Greenland. J. Quaternary Science, 21, 29-48.


Sparrenbom, C.J. Bennike, O., Bjorck, S., Lambeck, K., 2006. Holocene relative sea-level changes in the Qaqortoq area, southern Greenland. Boreas 35(2) (in press)


Lambeck, K., Purcell, A., Funder, S., Kj¾r, K., Larsen, E., Mšller, P., 2006. Constraints on the Late Saalian to early Middle Weichsellian ice sheet of Eurasia from field data and rebound modeling. Boreas (in press).



Last modified: 21 Mar 2006.