Contribution of Roughness to the Comprehension of Features on Ice Shelves and Implications for Ice Shelf Vulnerability

Abstract

Understanding the fate and stability of the Antarctic Ice Sheet is paramount for future projections of sea level rise in the coming centuries. Ice shelves---permanent, floating, sections of ice that fringe the coastline of Antarctica,---regulate the discharge of land-based ice into the ocean and are thought to buttress and stabilize the discharge of grounded ice upstream. Previous research has tied ice shelf collapse to the accelerated discharge of grounded ice into the ocean. However, our understanding of the processes that contribute to ice shelf weakening and demise remains underdeveloped. In this work, we aimed to improve our understanding of the processes that increase ice shelf vulnerability by developing a quantitative tool for measuring how fragmented an ice shelf is based on quantities that are increasingly available through remote sensing, such as ice thickness. We first explain how we can quantify the roughness of ice shelves and then calculate roughness of a series of ice shelves. We observe that consistent with previous studies, the roughness of ice shelves is largely determined by features associated with melting and fracturing of the ice. Basal melt carves out melt channels into the base of the ice shelf while fracture impart cracks (or crevasses) onto the ice shelf. We find that the topography of ice shelves is fractal, with the amplitude of roughness controlled by the melt rate. Next, we examine the discrete processes that are imparting roughness onto ice shelves and find that roughness is largest when basal melting and strain rate are largest. When both processes are active at the same time, the ice shelf becomes the roughest (or most fragmented). Finally, by using data obtained over the last two decades across a menagerie of ice shelves throughout Antarctica, we track how the roughness of ice shelves has changed over twenty years. Critically, we find that ice shelves have seen a statistically significant increase in roughness have also had a significant reduction in their overall size. This is particularly true for ice shelves in the vulnerable and changing Amundsen Sea. This hints that ice shelf roughness, which can be easily measured from remotely sensed data products, may be a powerful tool in tracking the demise of some ice shelves over time. Being able to predict exactly when a particular ice shelf may collapse is going to collapse may be impossible. However, we show that by using roughness in addition to other metrics, we may be able to identify which ice shelves are the most at risk and therefore gauge future scientific efforts toward studying those ice shelves.