Observations of Melting at the Base of Ronne Ice Shelf, Antarctica

We present several sets of observations from a site on Ronne Ice Shelf situated about 500 km from the ice front and 15 km from the western coast of Korff Ice Rise. These observations include measurements of water temperature and flow beneath the ice, measurements of temperature within the ice shelf and phase-sensitive radar measurements of its thinning rate. The latter data give us precise estimates of the basal melt rate, once the component of the thinning that results from horizontal divergence of the ice shelf flow has been removed. The thermistors within the ice shelf warm gradually as they approach the ice shelf base and this gives us an independent, consistent estimate of the melt rate, albeit less precise and averaged over a longer timescale. Using these data we can also estimate the vertical heat flux conducted into the ice shelf from the ocean. Our measurements of ocean temperature and velocity allow us to estimate the vertical heat flux from the ocean, using a conventional parameterisation of heat transfer in the turbulent boundary layer. The temperature and current measurements are multi-annual, but we only have a record of current at one point in the lower part of the water column. However, the current at this point is dominated by the tide, and we can put limits on the possible shear in the mean velocity from the spatial sampling of temperature and salinity afforded by the tidal excursion. Assuming that the velocity near the ice shelf base is also tidally dominated our estimate of basal melting based on our conventional boundary layer parameterisation is a factor two smaller than the observed melt rate. We discuss the likely cause and implications of the discrepancy.