Iceberg Calving
Approaching the Loose Tooth on the Amery Ice Shelf, Antarctica, to deliver field supplies by helicopter to a field party including Jeremy Bassis.
Photograph of GPS and seismic instrument deployment near the loose tooth on the Amery Ice Shelf, Antarctica. The blue box contains the GPS receiver and the seismic data acquisition unit.
Iceberg calving is the primary means of discharging ice from the Antarctic Ice Sheet into the Southern Ocean and, although large calving events occur sporadically, when they do occur they remove large amounts of mass in a near-instantaneous fashion. The time-scale between major calving events on ice shelves is long (typically several decades), and such events form part of the natural cycle of advance (by ice flow) and retreat (by calving) of the ice front. However, changes in calving rates have also been implicated in some of the most rapidly changing regions of Antarctica. This has been dramatically illustrated in accelerated calving leading to retreat and eventually disintegration of several ice shelves along the Antarctic Peninsula, e.g., the Larsen-B Ice Shelf collapsed over just 10 weeks in 2002.
• Field studies of ice shelf rift propagation
• Developing iceberg calving `laws'
• Modeling iceberg calving
Field studies of ice shelf rift propagation
Rifts, large fractures that penetrate the entire ice thickness, are precursors to iceberg calving events. These fractures can extend up to hundreds of kilometers and propagate for decades before becoming the detachment boundary of icebergs. Little is known about the forces and mechanisms that lead to rift initiation and propagation - partly because we have very few measurements against which hypotheses can be tested. To address this, we've been working with an international team of scientists to deploy global positioning system receivers (GPS) and seismometers around the tip of a propagating rift on the Amery Ice Shelf, East Antarctica. The field work has been done in conjunction with a program monitoring rift propagation using satellite imagery.
Parameterizations of iceberg calving
Another aspect of our work is the development of large-scale parameterizations of iceberg calving over much longer timescales that can, eventually, be incorporated into numerical ice sheet-shelf models and, in the future, global climate models. Below are two animations of a model that we have been using in which calving is controlled by the stress within the ice along with a random element. This movie shows calving from an ice shelf. Note the infrequent, sporadic detachment of relatively large icebergs.
In this case, calving events are more frequent, but much smaller in size.
