Feedback mechanisms and ice sheet behaviour

Two glacial episodes in Scandinavia -- but why was one more extensive than the other?

This is a very interesting paper on the behaviour of the Scandinavian Ice Sheet. For some time I have been interested in the manner in which feedback mechanisms operate within and on the edges of large ice masses. As readers of this blog will know, I have pondered occasionally on the role played by large troughs (such as Sognefjord in Norway and Nordvestfjord in East Greenland) in the efficient evacuation of ice and the dynamics of the ice mass. Assuming that in each successive glacial cycle these troughs are widened and especially deepened, we can also assume that the efficiency of ice transfer is improved -- but does that mean that ice sheets will get bigger and bigger in each successive glaciation? Not necessarily -- there might be ice edge advances at the trough outlets, but maybe ice edge retreat elsewhere because of ice capture in the trough catchments. In other words, there might be increased ice edge crenellation. This could all get very confusing -- and to their credit Henry Patten and others have already been thinking along these lines with respect to the BIIS.

The authors of the new Scandinavian paper concentrate on the role of gradual sediment filling of the low points in the landscape and the "capturing" of ice flow by spectacular features like the Norwegian Trough. With respect to the BIIS and the Celtic Sea arena, the BRITICE team have already been speculating on whether the Late Devensian Glaciation was the most extensive of all the Quaternary glaciations, partly because of the vast thickness of sea floor sediments across which the ice was flowing -- increased bed lubrication, sediment deformation, accelerated flow rates and a lower surface gradient are all interconnected.  Surging behaviour also comes to mind.  But what are the side effects of the "purges" that seem to have occurred in the Celtic Sea area?  Does a more extensive LGM mean that the glaciation was also more intensive?  Not necessarily.

Interesting questions so far, and not many answers......

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Gustav Jungdal-Olesen, Jane Lund Andersen, Andreas Born, and Vivi Kathrine Pedersen, 2024.
The influence of glacial landscape evolution on Scandinavian ice-sheet dynamics and dimensions
The Cryosphere, 18, 1517–1532, 2024

https://doi.org/10.5194/tc-18-1517-2024

Abstract. 
The Scandinavian topography and bathymetry have been shaped by ice through numerous glacial cycles in the Quaternary. In this study, we investigate how the changing morphology has influenced the Scandinavian ice sheet (SIS) in return. We use a higher-order ice-sheet model to simulate the SIS through a glacial period on three different topographies, representing different stages of glacial landscape evolution in the Quaternary. By forcing the three experiments with the same climate conditions, we isolate the effects of a changing landscape morphology on the evolution and dynamics of the ice sheet. We find that early Quaternary glaciations in Scandinavia were limited in extent and volume by the pre-glacial bathymetry until glacial deposits filled depressions in the North Sea and built out the Norwegian shelf. From middle–late Quaternary (   0:5 Ma) the bathymetry was sufficiently filled to allow for a faster southward expansion of the ice sheet causing a relative increase in ice-sheet volume and extent. Furthermore, we show that the formation of The Norwegian Channel during recent glacial periods restricted southward ice-sheet expansion, only allowing for the ice sheet to advance into the southern North Sea close to glacial maxima. Finally, our experiments indicate that different stretches of The Norwegian Channel may have formed in distinct stages during glacial periods since 0:5 Ma. These results highlight the importance of accounting for changes in landscape morphology through time when inferring ice-sheet history from ice-volume proxies and when interpreting climate variability from past ice-sheet extents.