GLACIAL REBOUND OF THE BRITISH-ISLES .1. PRELIMINARY MODEL RESULTS

Observations of sea-level change from localities around the British coastline indicate that major spatial and temporal variations have occurred over the past 15 000-10 000 yr. These observations provide a valuable data set for testing models of glacial rebound and for estimating the Earth's response to surface loading as well as for placing broad constraints on models of the ice sheet over the northern British Isles in Late Devensian time. Simple models have been developed to examine the criteria required for a high-precision rebound model suitable for an inversion of the observations of sea-level change for earth- and ice-model parameters. For such a model to have a precision of better than 1 m these requirements include: (1) introduction of the Fennoscandian and more distant ice sheets into the model both as contributions to the sea-level rise and to the crustal deformation of the associated changing ice and water loads; (2) an expansion of the ice and meltwater loads to very high spherical harmonic degree including terms up to about 240 for the water-load term; (3) the development of higher iteration solutions of the sea-level equation in order to model accurately the meltwater load contribution to sea-level change; (4) the introduction of loading cycles before the attainment of the last glacial maximum for both the British ice sheet and the other major but more distant ice sheets; and (5) the introduction of time-dependent coastlines during the period of rapid global sea-level rise. The sea-level predictions are strongly dependent on both earth-model and ice-model parameters but because observations are available from a wide range of locations within and beyond the former ice-sheet margins, some separation of the two types of parameters is possible. For example, the models exclude the possibility that a substantial ice load occurred over the North Sea between Scotland and Norway in Late Devensian time and that the maximum ice thickness over northern Great Britain is unlikely to have exceeded about 1500 m during the last glacial maximum. The earth model parameters that can be resolved are the lithospheric thickness and the upper mantle viscosity. A high resolution model incorporating the above model criteria and used to infer ice-and earth-model parameters from the observations of sea-level change is developed in the accompanying paper.