Mass balance of East Antarctic glaciers and ice shelves from satellite data

The velocity and mass discharge of nine major East Antarctic glaciers not draining, into the Ross or Filchner-Ronne Ice Shelves is investigated using interferometric synthetic aperture radar (InSAR) data from the European Remote-sensing Satellite I and 2 (ERS-1/2) and RADARSAT-1. The glaciers are: David, Ninnis, Mertz, Totten, Scott, Denman, Lambert, Shirase and Stancomb-Wills. InSAR IS used to locate then grounding line with precision. Ice velocity is measured with either InSAR or a speckle-tracking technique. Ice thickness is deduced from prior-determined ice-shelf elevation assuming hydrostatic equilibrium Mass fluxes are calculated both at the grounding line and at a flux gate located downstream. The grounding-line flux is compared to a mass input calculated from snow accumulation to deduce the glacier mass balance. The calculation is repeated at the flux gate downstream of the grounding line to estimate the average bottom melt rate of the ice Shelf under steady-state conditions. The main results arc: (1) Grounding lines are found several tells of km upstream of prior-identified positions, not because of a recent ice-sheet retreat but because of the inadequacy of prior-determined grounding-line positions. (2) No gross imbalance between outflow and inflow is detected oil the little glaciers being investigated gated, with an uncertainty of 10-20%. Prior-determined, largely positive mass imbalances were due to all incorrect localization of the grounding line. (3) High rates of bot torn melting (24 +/- 7 in Ice a(-1)) are inferred near grounding zones, where ice reaches the deepest draft. A few glaciers exhibit lower bottom inch, rates (4 +/- 7 in ice a(-1)). Bottom melting, however, appears to be a major source of mass loss oil Antarctic ice shelves.