The floating extent of the Antarctic Ice Sheet -- the ice shelves -- play a critical role in stabilizing the ice sheet through a process known as buttressing. This effect slows the flow of grounded ice into the ocean and thereby helps regulating the ice sheet's sea level rise con
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The floating extent of the Antarctic Ice Sheet -- the ice shelves -- play a critical role in stabilizing the ice sheet through a process known as buttressing. This effect slows the flow of grounded ice into the ocean and thereby helps regulating the ice sheet's sea level rise contribution. However, ice shelves are highly sensitive to (climate-driven) changes, which can cause thinning and structural weakening. This, in turn, can diminish their stabilizing influence and accelerate ice loss from the ice sheet. Given Antarctica’s vast potential to contribute to sea level rise, understanding the processes affecting ice shelf stability is essential for predicting future changes and reducing associated uncertainties.
Ocean-driven melting at the base of an ice shelf significantly influences its stability by driving ice thinning, grounding line retreat, and through basal channel formation. These channels, formed by meltwater plumes carving pathways along the ice base, are shaped by ice draft geometry, ocean dynamics and temperature. Basal channels concentrate melting and can weaken ice shelves by acting as structural weak points and promoting fractures that may lead to calving and retreat. On the other hand, basal channels can also stabilize ice shelves by localizing melt, potentially reducing overall thinning. Their evolution -- including changes in size, location, and intensity of melting -- is influenced by changes in ice flow and the availability and temperature of circumpolar deep water, which is expected to increase under climate change. Understanding basal channels and their role in ice shelf (in)stability is thus essential for accurately assessing the future behavior of the Antarctic Ice Sheet and its contributions to sea level rise.
In this thesis a method for detecting basal melting at high spatial resolution, called BURGEE (Basal melt rates Using REMA and Google Earth Engine), was developed and described in Chapter 2. BURGEE combines stereo-imagery from the Reference Elevation Model of Antarctica (REMA) with CryoSat-2 elevation data to obtain high-resolution ice shelf elevation changes, which through a mass conservation approach can be translated into basal melt rates. BURGEE's 50 m posting allows for capturing detailed melt patterns previously unresolved in coarser remote sensing products. Applied to the Dotson Ice Shelf, BURGEE revealed spatial variability within a major melt channel, influenced by a pinning point that affects ocean plume pathways. This method was developed to be scalable allowing for applications to other ice shelves to better understand ice shelf melt dynamics and stability across several ice shelves.
Using BURGEE in Chapter 3, high-resolution basal melt maps revealed that melt rates within ice shelf channels have been underestimated by 42-50% in products relying on altimetry-only. This underestimation has a significant impact on ice shelf stability assumptions, for which channel breakthrough times can be used as a proxy. As breakthrough times are highly controlled by the melt rate within the channels, these altimetry-only studies also significantly underestimate the time it would take for a channel to break through. While so far channels have not been observed to actually break through, they have been observed to cause significant fracturing once they reach a thin and vulnerable state. Channel-induced fracturing has further been observed to lead to ice shelf calving and retreat. The faster-than-previously-assumed channel breakthrough times -- and thus weakening -- exacerbates the vulnerability of ice shelves to channelized melting and consequent fracturing and retreat. Incorporating basal melting at high resolution into ice-sheet and ocean models is thus crucial for improving projections of ice shelf stability and global sea level rise.
In Chapter 4, BURGEE has further revealed sudden changes within the basal channel system on George VI Ice Shelf, marked by a 23 m surface lowering over just nine years. This rapid development coincided with increased ocean temperatures and salinity during the 2015 El Niño event, highlighting the influence of large-scale climate patterns on basal melting. The high resolution further revealed subtle shifts in ice flow indicative of fracturing, suggesting a combined weakening effect from basal melting and structural integrity causing changes and possible re-routing of the channel system. Such findings underscore the importance of monitoring dynamic ice shelf channels at a high resolution to better understand and predict their role in ice shelf weakening.
Together, these findings represent a significant advancement in our understanding of basal melting and its impact on ice shelf stability. This thesis has provided the tools and insights needed to detect, quantify, and analyze the spatial variability of basal melting at high spatial resolution. By uncovering the underestimation of channelized melting, identifying key drivers of channel evolution, and linking these processes to ice shelf weakening and retreat, this work has filled critical knowledge gaps. It emphasizes the importance of high-resolution observations and models in capturing the complex interactions between ocean dynamics, basal melting (especially within channels), and ice shelf integrity.