Abstract
ABSTRACTThe British and Irish Ice Sheet (BIIS) was highly dynamic during the Late Quaternary, with considerable regional differences in the timing and extent of its change. This was reflected in equally variable offshore ice‐rafted debris (IRD) records. Here we reconcile these two records using the FRUGAL intermediate complexity iceberg–climate model, with varying BIIS catchment‐level iceberg fluxes, to simulate change in IRD origin and magnitude along the western European margin at 1000‐year time steps during the height of the last BIIS glaciation (31–6 ka bp). This modelled IRD variability is compared with existing IRD records from the deep ocean at five cores along this margin. There is general agreement of the temporal and spatial IRD variability between observations and model through this period. The Porcupine Bank off northwestern Ireland was confirmed by the modelling as a major dividing line between sites possessing exclusively northern or southern source regions for offshore IRD. During Heinrich events 1 and 2, the cores show evidence of a proportion of North American IRD, more particularly to the south of the British Isles. Modelling supports this southern bias for likely Heinrich impact, but also suggests North American IRD will only reach the British margin in unusual circumstances.
Highlights
An ice sheet with a large marine component, such as the West Antarctic Ice Sheet today, is suspected to be dynamic, with major change occurring quickly but not spatially synchronously, leading to major consequences for iceberg flux rates, ocean circulation and, potentially, sea level (Hughes, 1975; MacAyeal, 1992; Bamber et al, 2009; Thomas, 2014)
The overall conclusions of the ice‐rafted debris (IRD) perspective on the peak and deglaciation phases of the last British and Irish Ice Sheet (BIIS) – that IRD is sourced fairly locally over 31–16 ka BP, except during some Heinrich events in some core locations, and that the likelihood of the mean North Atlantic Polar Front (NAPF) separating northward‐ from southward‐moving currents remained around the Porcupine Bank – have been shown to agree with the model simulations
A possible resolution of the %Neogloboquadrina pachyderma sinistral (Nps) inconsistencies leading to that Polar Front hypothesis is given, through the inferred presence of a cold tongue extending across the Atlantic south of Britain
Summary
An ice sheet with a large marine component, such as the West Antarctic Ice Sheet today, is suspected to be dynamic, with major change occurring quickly but not spatially synchronously, leading to major consequences for iceberg flux rates, ocean circulation and, potentially, sea level (Hughes, 1975; MacAyeal, 1992; Bamber et al, 2009; Thomas, 2014). The best studied past analogue for such a dynamic marine glacial system is the British and Irish Ice Sheet (BIIS) of the last glacial period (Clark et al, 2018). What is currently lacking in the literature for any past ice sheet, is a formal reconciliation of the detailed reconstruction of these two perspectives. Our approach to this reconciliation is to use the well‐ constrained BRITICE‐CHRONO reconstruction of the growth and retreat of the British–Irish Ice Sheet during the last glacial (31 to 15 ka BP) to compute potential iceberg
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