1. Antarctic ice shelf thicknesses derived from satellite altimetry Jennifer Griggs and Jonathan Bamber Bristol Glaciology Centre, University of Bristol

2. Motivation Reducing errors in mass budget estimates Need accurate estimate for modelling studies of shelf and sub-shelf cavity Initially completed case study for Larsen C GRL paper in press (Griggs, J.A. and J.L. Bamber, Ice shelf thickness over Larsen C, Antarctica derived from satellite altimetry, Geophysical Research Letters, Oct 2009) In the middle of extending to all ice shelves with area over 10km 2

3. Method Infer thickness from surface elevation assuming hydrostatic equilibrium where Z = thickness, e = elevation wrt sea level, δ = firn density correction, ρ w = density of water and ρ i = density of ice

4. Data Use ERS-1 geodetic phase Can’t just use DEM Don’t include GLAS in data rich regions due to dH/dt considerations

5. Data availability - Larsen C Black dots are data coverage White contours are elevation Coloured background is thickness

6. Validation of elevation – Larsen C Error = -2.3 ± 4.9 m Error = -1.7 ± 4.5 m if accounting for dH/dt between GLAS and ERS-1 Error = -0.5 ±1.1m in central area

7. Firn correction – Larsen C Regional atmosphere model run at 55 km used to force a steady state firn densification model. Accounts for temperature, accumulation and wind speed variability but not horizontal compaction or melting. Mean reduced to 10 m due to lack of melt

8. Validation of thicknesses – Larsen C

9. Error = -0.22±36.7m Error = +23.2±43.67m without accounting for melt in firn correction Error = -2.03±11.04m in central area Error = -1.45±68.5m within 10km of grounding line Random error in validation data = 12m

10. Conclusions and next steps Ice thickness can be inferred from the geodetic phase of ERS-1 within acceptable errors (<15% of mean thickness) Now need to apply to all ice shelves. Only consider those over 10km 2 Use MOA grounding and coast line supplemented by Eric Rignot’s SAR grounding lines to determine areas considered as floating

11. ERS coverage

12. Ice shelf thickness

13. Validation