Marine ice formation and deformation at the Southern McMurdo Ice Shelf, Antarctica
Professor Sean Fitzsimons
Marine ice forms from a mixture of glacial and sea water and accumulates at the bottom of many Antarctic ice shelves. It can occur in thick dense layers or fill in structural weaknesses, such as bottom crevasses. Its presence therefore influences the rheology and stability of ice shelves, which often buffer glaciers and ice streams. Although widespread in Antarctic ice shelves, little is known about the conditions for marine ice formation and its rheological behavior. My Ph.D. thesis aims to determine processes of marine ice formation from its chemical and physical properties. It also investigates the microstructural evolution of marine ice exposed to increasing strain. Ice samples were extracted in shallow ice cores (2-3m long) from the Southern McMurdo Ice Shelf, where marine ice is accessible from the shelf surface due to locally high ablation rates. In order to determine marine ice freezing rates and source water, ice chemical properties (water isotopes, total dissolved solids) are related to the output of a mixing and boundary layer freezing model. The morphology of the ice crystals further helps to determined modes of formation (accumulation of fast forming frazil ice crystals versus the slow advancement of a freezing front). Ice deformation is assessed by comparing crystal size and fabric evolution of marine and meteoric ice extracted in ice cores from a transect of increasing horizontal compression as the ice shelf flows toward shore. Surface strain along the transect was determined from a GPS survey of a network of velocity stakes. An improved understanding of marine ice formation and deformation gained in this study allows for better prediction of ice shelf behavior in a changing climate.