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

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

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

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

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

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

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

Validation of thicknesses – Larsen C

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

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

ERS coverage

Ice shelf thickness

Validation