Glacialisostatic adjustment and sealevel change around Greenland

Present-day sea-level change around Greenland is dominated by glacial-isostatic adjustment (GIA), which is the Earth's viscoelas-tic response to surface-load changes associated with the redistribution of continental ice and ocean water. The most prominent changes occurred after the Last Glacial Maximum (LGM, ca. 21kyr BP), which involved the melting of ice equivalent to ca. 130m of water when distributed evenly over the present-day ocean surface (Lambeck et al., 2000). We consider separately the changes in the Late Pleistocene ice sheets located outside of Greenland, and those involving the Greenland Ice Sheet (GIS) itself. The GIS's fluctuations are in turn divided between those following the LGM, and more recent changes such as the neoglaciation, when the ice sheet in some areas retreated behind its current margin before readvancing from ca. 4kyr BP (Weidick, 1996), and present-day changes.

Figure 45.1 presents modelled predictions of the GIA contribution to sea-level change around Greenland. The computation programs and input models are from the Research School of Earth Sciences, the Australian National University (e.g. Lambeck et al., 1998, 2000). The ice models are realistic spatial and temporal descriptions of the North American, European, Antarctic and Greenland Ice Sheets. A three-layered earth model is used, consisting of an elastic lithosphere of thickness h L, an upper mantle of viscosity hUM extending to the 670km seismic discontinuity, and a lower mantle of viscosity hLM extending to the core-mantle boundary, the mantle being treated as a Maxwell-vis-coelastic body. The earth-model parameter values used have been

Geophysics Gia ModelGeophysics Gia Model

Figure 45.1 Predictions of the contribution of glacial-isostatic adjustment to present-day sea-level change about Greenland (mmyr-1, positive indicating rising sea levels): (a) the contribution from changes in the Late Pleistocene ice sheets located outside of Greenland; (b) the total contribution from changes in the Late Pleistocene ice sheets, including Greenland (neglecting the neoglaciation); (c) the same as (b) but including a neoglacial part in the southwest Greenland Ice Sheet; (d) the contribution from present-day changes in the Greenland Ice Sheet. (See for colour version.)

inferred from previous GIA studies and are appropriate for regions such as Greenland that are made up of older cratonic units (e.g. Mitrovica, 1996; Lambeck et al., 1998). These values are hL = 80km, hUM = 5 x 1020Pas and hLM = 1 x 1022Pas.

Figure 45.1a presents the GIA contribution from changes in the ice sheets located outside of Greenland following the LGM. The result is rising sea levels of the order of several millimetres per year, decreasing from west to east (Tarasov & Peltier, 2002). This is largely due to Greenland's location on the collapsing forebulge that surrounds the former North American ice sheets. The falling sea level over Ellesmere Island (northwest corner) comes from the ongoing uplift following the deglaciation of the Innuitian Ice Sheet. An important point is that if the spatial description of the Innuitian were modified, it may significantly alter the results for northwest Greenland.

Figure 45.1b presents the contribution from past changes in all ice sheets, including the GIS. The GIS model (Fleming & Lambeck, 2004) defines the retreat of the expanded GIS to have been completed by 7.5ka, ignoring in this case the neoglaciation. Much greater spatial variability is observed, mirroring the observed marine limits (e.g. Funder & Hansen, 1996). The more-rapid sea-level changes occur where the GIS had expanded most

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