Cirques in the Transantarctic Mountains reveal controls on glacier formation and landscape evolution

Barr, Iestyn ORCID: https://orcid.org/0000-0002-9066-8738, Spagnolo, Matteo and Tomkins, Matt (2024) Cirques in the Transantarctic Mountains reveal controls on glacier formation and landscape evolution. Geomorphology, 445. 108970. ISSN 0169-555X

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Abstract

In this study, we analyse the morphometry of cirques in the Transantarctic Mountains (TAM) to understand regional glacier formation and landscape evolution since the onset of Cenozoic glaciations. We find that, unlike most glacierised regions worldwide, aspect bias for cirques in the TAM is not particularly strong, indicating that glaciers were able to form and cirques develop on slopes with a variety of aspects. This is perhaps unsurprising, given that Antarctica's climate has been conducive to long-lived and extensive glaciation for many millions of years. Surprisingly, where cirques in the TAM show an aspect bias, this is typically towards the North, NW and/or NE, rather than favouring South-facing slopes where direct solar radiation is comparatively limited. This lack of a poleward aspect bias is unlike most cirque populations globally and indicates that total solar insolation was not a key control on where former glaciers in the TAM were able to initiate. Instead, we argue that prevailing wind directions played a dominant role in controlling the slopes on which past glacier development was favoured. Specifically, South-facing slopes in the TAM are directly exposed to katabatic winds which originate from the interior of the East Antarctic Ice Sheet (EAIS). These slopes are therefore susceptible to wind deflation, with snow and ice being redistributed to lee-side slopes where it can accumulate due to protection from the wind. For this reason, North, NE and/or NW facing slopes may have favoured glacier development, and therefore resulted in a concentration of cirques with these aspects. This evidence suggests that most cirques in the TAM are no older 34 Ma, as outward radiating winds from the continent's interior could only have prevailed when the EAIS was present (in some form). By contrast, the very highest (and likely oldest) cirques in the TAM have more varied aspects, indicating that they may have formed before katabatic winds came to dominate, and by extension, before widespread growth of the EAIS at 34 Ma, and could perhaps have formed as far back as 60 Ma. In general, we find that cirques in the TAM have similar dimensions to those in other regions globally, despite having been occupied by glacial ice for far longer. Thus, our findings support a growing body of evidence which suggests that cirque size and glacier occupation times are not directly coupled, though there is some evidence of spatial variability in cirque size which might relate to the differences in the dynamics of former glaciers.