Glacial erosion during the last glacial cycle

The British / Irish Ice Sheet -- rates of erosion during a glacial episode.  The lighter the colour, the greater the erosion rate (maximum around 5mm per year).

This is a big new paper announcing the results of the latest modelling for the last glacial cycle, over approx the last 100,000 years. There are some interesting mismatches between the modelled ice sheet extent (the coloured area in the map above) and the mapped LGM ice edge.  As with the BRITICE - CHRONO team, the researchers have had difficulties with the ice edge that has been erroneously mapped in the outer part of the Bristol Channel;  the ice edge as modelled for the "ideal" ice cover during a glacial episode runs across Devon and Cornwall and close to Salisbury Plain, and I think that this is confirmed by ground truthing. Even if the edge shown is not correct, it is much closer than the widely accepted Weichselian limit shown on the map by the dashed line.

This is the first time any team has tried to quantify the amount of erosion associated with ice during a glacial episode. For the whole of the Eurasian ice sheet (with 3 components) the authors calculate the net volume of rock excavated during a glacial episode as c 130,000 cubic km -- that's a staggering amount of erosion.  The other thing to emerge from the study is that it is a mistake to assume that ice sheets have a broadly protective role apart from the erosion concentrated within and under ice streams.  They say that in reality what happens beneath thick ice is immensely complex, with different factors (climatic, glaciological, chronological and geological) operating in different ways in different locations.  Most erosion occurs not under fast-moving ice streams but under slowly moving ice in and near the ice sheet interiors.

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Patton, H., Hubbard, A., Heyman, J. et al. The extreme yet transient nature of glacial erosion. Nat Commun 13, 7377 (2022). 

https://doi.org/10.1038/s41467-022-35072-0

Abstract

Ice can sculpt extraordinary landscapes, yet the efficacy of, and controls governing, glacial erosion on geological timescales remain poorly understood and contended, particularly across Polar continental shields. Here, we assimilate geophysical data with modelling of the Eurasian Ice Sheet — the third largest Quaternary ice mass that spanned 49°N to 82°N — to decipher its erosional footprint during the entire last ~100 ka glacial cycle. Our results demonstrate extreme spatial and temporal heterogeneity in subglacial erosion, with rates ranging from 0 to 5 mm a−1 and a net volume equating to ~130,000 km3 of bedrock excavated to depths of ~190 m. A hierarchy of environmental controls ostensibly underpins this complex signature: lithology, topography and climate, though it is basal thermodynamics that ultimately regulates erosion, which can be variously protective, pervasive, or, highly selective. Our analysis highlights the remarkable yet fickle nature of glacial erosion — critically modulated by transient ice-sheet dynamics — with its capacity to impart a profound but piecemeal geological legacy across mid- and high latitudes.

The three components of the Eurasian Ice Sheet, showing rates of erosion during the last glacial cycle.