Using radar to determine the mechanical and thermodynamic effect of tides on an ice shelf

Abstract:

Understanding how fast the ocean melts Antarctic ice shelves, which are known to restrain the flow of ice from the continental interior, is important to future ice sheet contributions to global sea level rise. Dependant on oceanographic processes delivering ocean heat from the Southern Ocean to the ice, changing rates of ice shelf basal melting ultimately contribute to variations in ice shelf thickness that can affect the discharge of grounded ice into the ocean. Being able to understanding and then predict the way basal melting responds to a changing ocean, requires ocean models that include fully interactive ice shelves and melting processes within their domain. Although such ocean models exist, their performance in the sub-ice shelf part of the domain is very difficult to optimise and validate. Highly accurate measurements of melt rates can be provided by phase-sensitive radars (e.g. pRES), although these have been limited to long term averages. Recent developments by BAS and UCL however, have provided a lightweight, low-power and relatively low cost radar for year-round autonomous operation (ApRES), delivering long time series of ice thickness changes. At tidal time scales however, ice shelves respond elastically to tilting, with significant fluctuations in vertical strain that will appear as apparent basal melting or even freezing. To determine the true basal melt rate at tidal time scales these radar observed vertical strain fluctuations must be removed. At Site 5 on Ronne Ice Shelf, the combined availability of radar-derived melt rates, independent measurements from oceanographic instruments beneath the ice shelf, and GPS strain observations provide a powerful test of both how the ocean interacts with the ice shelf base and the tidally induced melt rates. Using these data we will discuss our ability to accurately predict the temporal details of melt rates beneath ice shelves using ApRES radar.