Investigating longitudinal fractures along ice-shelf estuaries

Abstract:

The recent discovery of the Petermann Estuary with its associated longitudinal fractures indicates a potential new ice-shelf weakening mechanism. To date, longitudinal fractures have not been found beneath any ice-shelf rivers, including the upstream reach of Petermann River. We have previously discovered, however, that fractures exist in the downstream reach of the Petermann River where flow reversals are identified; fractures therefore appear to be a consequence of ice-shelf estuary formation.

These fractures are located in the center of the Petermann Ice Shelf, where ice-shelf stresses are otherwise at a minimum, suggesting that the estuary likely aided in concentrating stress and initiating cracks. Estuarine weakening may be driven by increased thinning in the channel, as relatively warm ocean water enhances incision, and/or by loading/unloading of surface meltwater and ocean water resulting from sea-ice obstructions at the estuary mouth and tides. However, the physical mechanisms driving longitudinal fracture development remain unknown.

We use the first numerical model of ice-shelf estuaries to investigate the evolution of the Petermann Ice Shelf Estuary and associated longitudinal fractures. We use a new viscoelastic model that combines both ice-shelf flexure and ice flow to explore both estuary formation and weakening. As the Petermann Estuary sits atop a basal channel, we use our model to understand the relative importance of basal melting and surface melting in estuary formation, and then consider the influence of enhanced incision at the estuary mouth on fracture development. Finally, we use the model to consider ice-shelf stress perturbations and flexure resulting from loading/unloading of meltwater and ocean water in response to tides and sea-ice obstructions. We constrain the model with ICESat-2 data of surface topography changes through time, and WorldView satellite images of sea-ice blockages at the estuary mouth.