Shevchenko, V. P., 2010. Aerosols over the Russian Arctic seas. In
Nikiforov, S. (ed.), Seabed Morphology of the Russian Arctic
Shelf. New York: Nova Science Publishers, Inc, pp. 87–92.
Shevchenko, V. P., Lisitsyn, A. P., Polyakova, E. I., Dethleff, D.,
Serova, V. V., and Stein, R., 2002. Distribution and composition
of sedimentary material in the snow cover of arctic drift ice
(Fram Strait). Doklady Earth Sciences, 383(3), 385–389.
Stein, R., 2008. Arctic Ocean Sediments: Processes, Proxies and
Paleoenvironment. Developments in Marine Geology, 2nd edn.
Amsterdam: Elsevier. 592 pp.
Svendsen, H., Beszczynska-Møller, A., Hagen, J. O., Lefauconnier,
B., Tverberg, V., Gerland, S., Ørbæk, J. B., Bischof, K., Papucci,
C., Zajaczkowski, M., Azzolini, R., Bruland, O., Wiencke, C.,
Winther, J.-G., and Dallmann, W., 2002. The physical environment of Kongsfjorden–Krossfjorden, an Arctic fjord system in
Svalbard. Polar Research, 21(1), 133–166.
Syvitski, J. P. M., Andrews, J. T., and Dowdeswell, J. A., 1996. Sediment deposition in an iceberg-dominated glacimarine environment, east Greenland: basin fill implications. Global and
Planetary Change, 12, 251–270.
Szczucinski, W., and Zajaczkowski, M., 2012. Factor controlling
downward fluxes of particulate matter in glacier-contact and
non-glacier contact settings in a subpolar fjord (Billefjorden,
Svalbard). International Association of Sedimentologists. Special Publication, 44, 369–386.
Trusel, L. D., Powell, R. D., Cumpston, R. M., and Brigham-Grette,
J., 2010. Modern glacimarine processes and potential future
behaviour of Kronebreen and Kongsvegen polythermal tidewater glaciers, Kongsfjorden, Svalbard. In Howe, J. A., Austin,
W. E. N., Forwick, M., and Paetzel, M. (eds.), Fjord Systems
and Archives. Geological Society, London, Special Publications,
344, pp. 89–102.
Warren, C. R., 1992. Iceberg calving and the glacioclimatic record.
Progress in Physical Geography, 16(3), 253–282.
Cross-references
Energy Resources
Ice-rafted Debris (IRD)
GLACIO(HYDRO)-ISOSTATIC ADJUSTMENT
Kurt Lambeck
Research School of Earth Sciences, Australian National
University, Acton ACT, Australia
Synonyms
Glacial rebound; Isostasy
Definition
Isostasy refers to the response of the Earth to surface loading. Glacio-hydro-isostasy refers to the specific case of
surface ice and water loads during glacial cycles. The most
important observation of this process is the change in sea
levels around the world.
Introduction
Isostatic adjustment of the Earth refers to the response of
the Earth to changes in surface loading. The classic
examples are the Airy or Pratt models (Watts, 2001) in
which the surface load (of, for example, sediments) is
supported locally either by a deflection of the crust
(Airy) or by a change in crustal density (Pratt) beneath
the load such that, at some deeper and constant depth in
the mantle, pressures are constant. In these models, the
crust (or lithosphere) does not support shear stresses. In
models of regional isostatic adjustment (e.g., the Vening
Meinesz model), the load is supported by the elastic
strength of the crust or lithosphere and by the buoyancy
forces acting at the base of the layer (Heiskanen and
Vening-Meinesz, 1958). In these regional elastic models,
small-amplitude, short-wavelength bulges form in the
crustal deformation around the load, and in the geological
literature, reference is sometimes made to a lithospheric
forebulge. In both cases, the mantle is represented as a
zero-viscosity fluid and the isostatic state is indicative of
the Earth’s deformational response only when the loading
histories are longer than the relaxation time of the mantle.
This relaxation time is characteristically of the order of 10
4
years, and the models are not appropriate for analyzing the
response of the Earth-ocean system to changing glacial
loads where both the mantle flow and gravity field
changes are dominant factors in determining the shape of
the solid Earth and ocean surface.
The Earth’s response to changing ice and
water loads
The glacio-hydro-isostatic adjustment refers to the Earth’s
response to the changing ice and water surface loads during glacial cycles, particularly to the last phase of deglaciation, that have characteristic load-cycle time scales of
10
3
–10
5 years, of similar magnitude as the mantle relaxation times. Hence response models must consider the flow
induced in the mantle by the surface loading cycle, and in
consequence, the response continues for some thousands
of years after the ice loads have stabilized.
When ice sheets grow, the crust and lithosphere beneath
the ice subsides as mantle materials flow away from the
stressed regions. At the same time, water is taken out of
the oceans to feed the growing ice sheets, unloading the
underlying mantle and resulting in ocean floor uplift relative to the center of mass of the Earth. The reverse occurs
during the decay phase of the ice cycle. The glacio-hydroisostasy is therefore a global phenomenon, and models of
which will have to consider both the ice and water loads
through time.
Several observational measures of the Earth’s response
exist: (i) the deformation of the land surface and this is
measured by geodetic methods, most notably by GPS,
(ii) changes in the planet’s gravity field as both internal
and surface mass redistribution occurs and this is measured with gravity meters as well as inferred from perturbations in Earth-satellite orbits, (iii) changes in the
Earth’s rotation measured by astronomical and satellite
methods, and (iv) changes in sea-level as measured by tide
gauges and as preserved in the geological record. The
294
GLACIO(HYDRO)-ISOSTATIC ADJUSTMENT
Nikiforov, S. (ed.), Seabed Morphology of the Russian Arctic
Shelf. New York: Nova Science Publishers, Inc, pp. 87–92.
Shevchenko, V. P., Lisitsyn, A. P., Polyakova, E. I., Dethleff, D.,
Serova, V. V., and Stein, R., 2002. Distribution and composition
of sedimentary material in the snow cover of arctic drift ice
(Fram Strait). Doklady Earth Sciences, 383(3), 385–389.
Stein, R., 2008. Arctic Ocean Sediments: Processes, Proxies and
Paleoenvironment. Developments in Marine Geology, 2nd edn.
Amsterdam: Elsevier. 592 pp.
Svendsen, H., Beszczynska-Møller, A., Hagen, J. O., Lefauconnier,
B., Tverberg, V., Gerland, S., Ørbæk, J. B., Bischof, K., Papucci,
C., Zajaczkowski, M., Azzolini, R., Bruland, O., Wiencke, C.,
Winther, J.-G., and Dallmann, W., 2002. The physical environment of Kongsfjorden–Krossfjorden, an Arctic fjord system in
Svalbard. Polar Research, 21(1), 133–166.
Syvitski, J. P. M., Andrews, J. T., and Dowdeswell, J. A., 1996. Sediment deposition in an iceberg-dominated glacimarine environment, east Greenland: basin fill implications. Global and
Planetary Change, 12, 251–270.
Szczucinski, W., and Zajaczkowski, M., 2012. Factor controlling
downward fluxes of particulate matter in glacier-contact and
non-glacier contact settings in a subpolar fjord (Billefjorden,
Svalbard). International Association of Sedimentologists. Special Publication, 44, 369–386.
Trusel, L. D., Powell, R. D., Cumpston, R. M., and Brigham-Grette,
J., 2010. Modern glacimarine processes and potential future
behaviour of Kronebreen and Kongsvegen polythermal tidewater glaciers, Kongsfjorden, Svalbard. In Howe, J. A., Austin,
W. E. N., Forwick, M., and Paetzel, M. (eds.), Fjord Systems
and Archives. Geological Society, London, Special Publications,
344, pp. 89–102.
Warren, C. R., 1992. Iceberg calving and the glacioclimatic record.
Progress in Physical Geography, 16(3), 253–282.
Cross-references
Energy Resources
Ice-rafted Debris (IRD)
GLACIO(HYDRO)-ISOSTATIC ADJUSTMENT
Kurt Lambeck
Research School of Earth Sciences, Australian National
University, Acton ACT, Australia
Synonyms
Glacial rebound; Isostasy
Definition
Isostasy refers to the response of the Earth to surface loading. Glacio-hydro-isostasy refers to the specific case of
surface ice and water loads during glacial cycles. The most
important observation of this process is the change in sea
levels around the world.
Introduction
Isostatic adjustment of the Earth refers to the response of
the Earth to changes in surface loading. The classic
examples are the Airy or Pratt models (Watts, 2001) in
which the surface load (of, for example, sediments) is
supported locally either by a deflection of the crust
(Airy) or by a change in crustal density (Pratt) beneath
the load such that, at some deeper and constant depth in
the mantle, pressures are constant. In these models, the
crust (or lithosphere) does not support shear stresses. In
models of regional isostatic adjustment (e.g., the Vening
Meinesz model), the load is supported by the elastic
strength of the crust or lithosphere and by the buoyancy
forces acting at the base of the layer (Heiskanen and
Vening-Meinesz, 1958). In these regional elastic models,
small-amplitude, short-wavelength bulges form in the
crustal deformation around the load, and in the geological
literature, reference is sometimes made to a lithospheric
forebulge. In both cases, the mantle is represented as a
zero-viscosity fluid and the isostatic state is indicative of
the Earth’s deformational response only when the loading
histories are longer than the relaxation time of the mantle.
This relaxation time is characteristically of the order of 10
4
years, and the models are not appropriate for analyzing the
response of the Earth-ocean system to changing glacial
loads where both the mantle flow and gravity field
changes are dominant factors in determining the shape of
the solid Earth and ocean surface.
The Earth’s response to changing ice and
water loads
The glacio-hydro-isostatic adjustment refers to the Earth’s
response to the changing ice and water surface loads during glacial cycles, particularly to the last phase of deglaciation, that have characteristic load-cycle time scales of
10
3
–10
5 years, of similar magnitude as the mantle relaxation times. Hence response models must consider the flow
induced in the mantle by the surface loading cycle, and in
consequence, the response continues for some thousands
of years after the ice loads have stabilized.
When ice sheets grow, the crust and lithosphere beneath
the ice subsides as mantle materials flow away from the
stressed regions. At the same time, water is taken out of
the oceans to feed the growing ice sheets, unloading the
underlying mantle and resulting in ocean floor uplift relative to the center of mass of the Earth. The reverse occurs
during the decay phase of the ice cycle. The glacio-hydroisostasy is therefore a global phenomenon, and models of
which will have to consider both the ice and water loads
through time.
Several observational measures of the Earth’s response
exist: (i) the deformation of the land surface and this is
measured by geodetic methods, most notably by GPS,
(ii) changes in the planet’s gravity field as both internal
and surface mass redistribution occurs and this is measured with gravity meters as well as inferred from perturbations in Earth-satellite orbits, (iii) changes in the
Earth’s rotation measured by astronomical and satellite
methods, and (iv) changes in sea-level as measured by tide
gauges and as preserved in the geological record. The
294
GLACIO(HYDRO)-ISOSTATIC ADJUSTMENT