Glacial geology and glaciology of the last mid-latitude ice sheets

Abstract

Satellite imagery and data from ground surveys are used to reconstruct the integrated pattern of the principal longitudinal and transverse features produced on a continent-wide scale by the last ice sheets in Europe and North America. From modern analogues, it is argued that most longitudinal features reflect flow in the outer zone of the ice sheet, and that most major transverse features reflect relatively stable ice-sheet margins. These principles are tested and, using them alone, detailed patterns for the decay of the last ice sheets in North America, Europe and the British Isles are produced, and periods during which they attained near steady-states identified. These patterns can be calibrated by dated sequences to yield deglaciation isochrons. Application of glaciological models to these geological reconstructions generates detailed prediction of net ablation for the period of ice-sheet decay and, by using evidence of last glaciation stratigraphy, models of the dynamic behaviour of the ice sheets throughout the last glacial period are constructed. These enable volumetric changes, oceanic isotopic changes and erratic dispersal pathways to be reconstructed. Erratic dispersal patterns give a good indication of the long-term distribution of centres of ice sheet mass. Discrepancies between predicted and empirical oceanic isotopic records indicate ways in which the conventional continental timescale of glacial change must be altered to fit the better-dated deep ocean record. In addition discrepancies between predicted and empirical erratic dispersal patterns suggest that conventional views of ice-sheet behaviour based on high latitude models may be inappropriate to the dynamically more active mid-latitude ice sheets based in large part on deformable sediment beds.

The California current system during the last 136,000 years: response of the North Pacific High to precessional forcing

“…The calculated NINO3 index (Clement et al, 1999) and the estimated volume of the Laurentide ice sheet (Boulton et al, 1985) are shown for comparison. Blue and green crosses indicate the age controls for Sites 1014 and 1016, respectively, by 14 C dating and oxygen isotope stratigraphy.…”

“…This decline was attributed to a depressed summer North Pacific High influenced by the semipermanent development of a high-pressure cell over the expanded Laurentide ice sheet over continental North America (Kutzbach and Wright, 1985;Lyle et al, 1992). However, paleo-SST change at Site 1014 did not fully agree with the estimated volume change of the Laurentide ice sheet (Boulton et al, 1985). In particular, a low SST and abundant C. pelagicus indicate a strong California Current in late MIS 4; however, the second-largest expanse of the Laurentide ice sheet during the last glacial period also occurred during this time (Fig.…”

The palaeoglaciology of the central sector of the British and Irish Ice Sheet: reconciling glacial geomorphology and preliminary ice sheet modelling

“…Although there have been some attempts to reconstruct the palaeoglaciology of the last BIIS (Boulton et al, 1977(Boulton et al, , 1985, these reconstructions have been based on either nonsystematic mapping of spatially limited data, or inverse approaches using sea level histories (e.g. Shennan et al 2002).…”

On the reconstruction of palaeo-ice sheets: Recent advances and future challenges

“…drumlins) formed in a radial pattern close to the ice margin and mostly during deglaciation (e.g. Boulton et al, 1985). As such, these reconstructions often depicted a radial pattern of flow from one or more relatively stationary ice domes (Figure 2a,b).…”

“…The Antarctic and 6 reconstructions of the last mid-latitude ice sheets (e.g. Boulton et al, 1985;Dyke and Prest, 1987). The prevailing paradigm was that the mapped ice flow indicators (e.g.…”