High-resolution numerical simulation of Younger Dryas glaciation in Scotland

Abstract

We use a 500 m resolution three-dimensional thermomechanical ice -sheet model forced by a scaled GRIP temperature pattern to retrodict the extent of glaciers during the Younger Dryas episode in Scotland. Using empirical data from sources spanning half a century we systematically perturb temperature depression, precipitation distribution, and the amount of basal sliding to identify the parameter space that most closely reproduces the glacier margins identified from field investigations. Arithmetic comparison of predicted ice cover with empirical glacier extent enables mismatch to be quantified and an 'optimum fit' timeslice to be identified. This 'best-fit' scenario occurs with a maximum mean annual temperature depression from present of 10 C and steep eastward and northward gradients imposed on a modern precipitation distribution, coupled with restricted basal sliding. Even small deviations around these values produce considerably less well-fitting glacier configurations, suggesting that only a narrow range of optimal parameterisation exists. Mismatch between modelled and empirically reconstructed glacier extents occurs as a consequence of local conditions not accommodated by the model, such as wind-blown snow accumulation and lake (loch) bathymetry, and where geological evidence is equivocal. At the domain scale, however, our simulation suggests that inception of Scottish glaciers occurs rapidly, and leads to a coherent ice cap within 400 years of initial climatic cooling. According to our model, the ice cap begins to decay relatively early in the stadial, probably as a result of increasing aridity leading to net thinning and recession of many of its margins, with final and catastrophic collapse of the ice cap occurring largely within a century.

The glacial geomorphology of the Loch Lomond Stadial in Britain: a map and geographic information system resource of published evidence

“…The proposed limits of the Western Highland ice field in Scotland have been refined, but are not too dissimilar to early reconstructions (Sissons, 1967) and are supported by the results of numerical modelling (Golledge et al, 2008). However, at some locations, including both Sutherland in northwest Scotland and the English Lake District, more detailed remapping of geomorphology and an improved understanding of glaciological theory have been employed to show that plateau ice fields nourished extensive valley and cirque glacier systems (Brown et al, 2011(Brown et al, , 2013Lukas & Bradwell, 2010;Lukas & Lukas, 2006a;McDougall, 2001McDougall, , 2013Rea, Whalley, Evans, Gordon, & McDougall, 1998), thereby replacing earlier notions of more restricted, alpine styles of glaciation (Sissons, 1977(Sissons, , 1980.…”

“…The addition of absolute dates from the literature to this database will enable a more detailed understanding of the retreat dynamics of LLS ice. Although numerical modelling has previously been undertaken to determine the extent of LLS ice (Golledge et al, 2008), the outputs of this project provide a landform record which has the potential to aid in developing models to more accurately reconstruct glacier dynamics.…”

“…Secondly, it is conceivable, if not likely, that these LLS maximum extents were not reached synchronously (Ballantyne, 2012;Golledge, Hubbard, & Sugden, 2008). It is also possible that some features that were not formed by LLS glaciers may have been erroneously included.…”

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

“…Thus, the model includes the minimal requirements for a dynamic ice sheet model, specifically a 2-dimensional ice flow and free surface evolution. By ignoring temperature evolution within and at the base of the ice and any effects of longitudinal stresses our numerical ice sheet model is there for less sophisticated than previous attempts for modelling the BIIS or the Younger Dryas ice cap (Boulton and Hagdorn, 2006;Hubbard, 1999;Golledge et al, 2008).…”

Using the surface profiles of modern ice masses to inform palaeo-glacier reconstructions

“…On the other hand, numerical models formulated from physics are now routinely used (e.g. Boulton and Hagdorn, 2006;Hubbard et al, 2006;Golledge et al, 2008) to stimulate three-dimensional ice masses (e.g. Fig.…”