Insights on the formation of longitudinal surface structures on ice sheets from analysis of their spacing, spatial distribution, and relationship to ice thickness and flow

Abstract

Longitudinal surface structures (LSSs) are prevalent upon the ice streams, ice shelves, and outlet glaciers of ice sheets. These features inform our understanding of past and present ice sheet behavior. However, consensus regarding their genesis has not been reached. Here we analyze 42,311 LSS segments mapped across Antarctica together with geophysical data to determine their morphological and glaciological properties. Most LSSs are spaced 450 to 1500 m apart, a distance positively correlated with the width of the ice flow unit on which they occur. The start points (upstream end locations) of LSSs have diverse ice thicknesses and velocities. The majority of LSSs occur where ice flow is converging or broadly parallel, and they are prominent at ice confluences. Some occur at slow‐flowing ice stream onsets. Occasionally, LSSs relate to sudden variations in basal shear stress due to basal perturbations. From these observations, we argue that LSSs are the consequence of increased strain which occurs during the lateral compression and longitudinal extension of ice: (i) converging/flowing into a channel (this scenario characterizes most LSSs), (ii) at the onset of ice streaming, (iii) at flow unit confluence, and (iv) as ice flows over and around a basal perturbation.

Reconstructing ice‐flow fields from streamlined subglacial bedforms: A kriging approach

“…We identify three sites (ellipses in Figure 5 a and e) where a prominent basal ridge or bump seems to have caused flow divergence on its stoss side and convergence on its lee side. Similar 'dipoles' in C have been observed for the Antarctic Ice Sheet (Ng, 2015;Ely et al, 2017).…”

“…Figure 5e and 5g with the bed DEM in Figure 5a shows that the ripple amplitudes are strongest in the upper part of the Tweed Valley where the underlying topography is rugged (area enclosed by dashed curves in Figure 5a, e and g). Similar 'dipoles' in C have been observed for the Antarctic Ice Sheet (Ng, 2015;Ely et al, 2017). This correlation suggests that the ripples record perturbations of the ice flow by undulating bed topography (Gudmundsson, 2003;Ng et al, 2018b) on length-scales of several to~10 km.…”

Widespread distribution of supraglacial lakes around the margin of the East Antarctic Ice Sheet

“…Ice surface depressions related to underlying bedrock are likely to persist and are known to anchor lakes in the same location each year 1,3 . In other locations, longitudinal surface structures (known as ‘flow-stripes’) develop as a result of increased strain, particularly in areas of flow acceleration and confluence 47,48 . Large numbers of highly elongate SGLs are often found in the intervening troughs between flow-stripes (Figs 2a and 5b) and similar troughs can also form at the lateral shear margins of outlet glaciers/ice shelves 33 , where meltwater production might also be enhanced by the lower albedo of adjacent rock-walls (e.g.…”

Recent understanding of Antarctic supraglacial lakes using satellite remote sensing

“…Surface depressions are also controlled by the location of basal channels that are incised by sub-surface melting (Dow et al, 2018) and basal crevasses (McGrath et al, 2012) because thinner ice in these regions that has reached hydrostatic equilibrium will sit lower in the water. Surface depressions can also be associated with flow stripes, shear-margins and suture zones (Banwell et al, 2014;Bell et al, 2017;Ely et al, 2017;Glasser and Gudmundsson, 2012;Luckman et al, 2014;Reynolds and Smith, 1981). Reduced firn air content and ice surface topography are therefore first-order controls on SGL locations.…”