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Suture zones are abundant on Antarctic ice shelves and widely observed to impede fracture propagation, greatly enhancing ice-shelf stability. Using seismic and radar observations on the Larsen C Ice Shelf of the Antarctic Peninsula, we confirm that such zones are highly heterogeneous, consisting of multiple meteoric and marine ice bodies of diverse provenance fused together. Here we demonstrate that fracture detainment is predominantly controlled by enhanced seawater content in suture zones, rather than by enhanced temperature as previously thought. We show that interstitial seawater can reduce fracture-driving stress by orders of magnitude, promoting both viscous relaxation and the development of micro cracks, the incidence of which scales inversely with stress intensity. We show how simple analysis of viscous buckles in ice-penetrating radar data can quantify the seawater content of suture zones and their modification of the ice-shelf's stress regime. By limiting fracture, enhancing stability and restraining continental ice discharge into the ocean, suture zones act as vital regulators of Antarctic mass balance. Suture zones are abundant on Antarctic ice shelves and widely observed to impede fracture propagation. Here we show that fracture detainment is principally controlled by the zones' enhanced seawater contents, reducing fracture-driving stresses by orders of magnitude and therefore greatly enhancing stability. [ABSTRACT FROM AUTHOR]

Iceberg calving contributes more than half of mass loss in both Greenland and Antarctica.Despite its importance, the dynamic of calving glaciers are only partially understood. Weanalyse a model of calving based on linear elastic fracture mechanics, extending prior workdue to van der Veen (1998). Crack propagation is assumed to occur along a predefined,vertical failure plane until the stress intensity factors at the tips of two mutually alignedvertical crevasses reaches the "fracture toughness" of ice. One of the crevasses extendsupwards from the base, and the other downwards from the surface, with the latter potentiallyconfining water that extends upwards to a prescribed water table. Such solutions are stable iffurther lengthening of the cracks results in an increase in the stress intensity factors.Calving occurs when the stable solution disappears under an infinitesimal changes ingeometrical (thickness, distance from ice edge) or hydrological (water table height)parameter. By contrast with van der Veen, we model both crevasses simultaneously and computestress intensity factors directly using a displacement discontinuity method rather than relyingon tabulated or interpolated elasticity kernels. We find that, for a prescribed water tableheight, calving occurs at a critical ice thickness (or vice versa), generalizing the more ad hocmodel of Nick et al. (2010). This is a joint work with Christian Schoof. [ABSTRACT FROM AUTHOR]