Modelling and remote sensing of meltwater drainage on Antarctic ice shelves

• Main Author: Spergel, Julian Jacob
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: Geophysics; Computer science; Hydrology; Ice shelves; Drainage; Meltwater; Runoff; Climatic changes; Antarctic; Amery; Amery Ice Shelf; Riiser-Larsen; Roi Baudouin; Nivlisen; Antarc*; Ice Shelf; Ice Shelves
• Online Access: https://doi.org/10.7916/swez-dp81

In this thesis, I have used remote sensing and modeling techniques to investigate Antarctic ice shelf surface hydrology with the purpose of answering three key questions: 1) How do surface drainage systems evolve over a typical summertime melt season, over several consecutive melt seasons, and over several decades? 2) What controls the expansion of surface hydrology networks? and 3) Will surface drainage expand into areas vulnerable to hydrofracture and important for buttressing when meltwater volume increases in a warmer, future climate? In Chapter 1, our analysis of satellite observations of Amery Ice Shelf’s surface drainage networks suggests that their downstream extent varies inter-annually, that this variability is not simply the result of inter-annually variability in melt rates, and that ice-shelf topography plays a crucial role. Consecutive years of extensive melting lead to year-on-year expansion of the drainage system, potentially through a link between melt production, refreezing in firn, and the maximum extent of the lakes at the downstream termini of drainage. These mechanisms are important when evaluating the potential of drainage systems to grow in response to increased melting, delivering meltwater to areas of ice shelves vulnerable to hydrofracture. In Chapter 2, we use high resolution elevation data to delineate hydrologic catchments on Amery, Roi Baudouin, Larsen C, Nivlisen, and Riiser-Larsen Ice Shelves. We compare our results spatially with modelled present-day melt production, future melt predictions, and stress-based vulnerability to hydrofracture, to examine the controls on these hydrologically important characteristics of the topography. The high volume elevation data present computational challenges that cannot be overcome with traditional data analysis workflows. Therefore, pre-processing for catchment delineation is made possible by parallelizing these tasks with the computational power of cloud-based cluster computing. Catchments with high basin volumes are found clustered near grounding lines and nunataks, and these catchments are bordered down-glacier by broader, low volume catchments. We hypothesize that once meltwater production fills these catchments, we should expect to see overflow of meltwater, extending drainage systems downstream to the calving fronts or into areas vulnerable to hydrofracture. In Chapter 3, we use the digital elevation data from Chapter 2 as the input for an idealizedwater routing model of the eastern and western Amery Ice Shelf, Nivlisen Ice Shelf, and Roi Baudouin Ice Shelf to investigate this drainage network expansion. In our comparison with previous observational studies, we find that our modelled drainage networks show similar drainage network patterns, despite having several discrepancies in drainage network arrangement and water ponding locations. We use our model to investigate the expansion of the drainage network with average annual melt from the regional climate model RACMO. In one model run, we use the spatial distribution of average annual melt from an overlapping RACMO subset, in the other, we input a spatially-averaged melt production of the same subset of RACMO. We compare the results of these simulations to investigate if the expansion of these drainage systems is controlled predominantly by near-surface climate via water input, or if topography also plays a role. We find variability both between drainage systems and within a single drainage system, and that within all of our selected drainage systems, topography exerts some control over expansion. The responsiveness of a drainage network system to spatially variable meltwater input may affect how susceptible the system is to expansion, thus the spatial distribution of melt input must be represented in an ice shelf stability projection model. As melt input increases in a warmer future Antarctic, it will be increasingly important tounderstand how surface melting may affect ice shelf stability. This thesis shows several proof-of-concept approaches towards modelling future expansion of surface drainage networks on Antarctic ice shelves. We find that the spatial variability of melt does impact the expansion rate of drainage networks across ice shelf areas potentially vulnerable to hydrofracture. This thesis posits that with more year-on-year meltwater drainage system growth, meltwater-induced hydrofracture may become an increasingly regular occurrence on Antarctic ice shelves.