Polar Ice Sheets and Ice Shelves Mass Balance
Polar Ice Sheets and Ice Shelves: Mass Balance, Uncertainties, and Potential Improvements Robert H Thomas…etc
Estimating ice-sheet mass balance: techniques • • • Mass-budget, compares total snow accumulation with losses by ice discharge and melt runoff Repeated altimetry, to estimate volume changes Temporal changes in gravity, to infer mass changes
Mass budget: uncertainties Antarctica Greenland (Gt a-1) Snowfall + 130 (7%) + 25 (5%) Ice flow + 93 (5%) + 25 (5%) Melt runoff Very small + 30 (10%) Mass balance (mm/yr SLE) + 160 (+ 0. 5) + 46 (+ 0. 15)
Altimetry: uncertainties SRALT Topography effects Changing dielectrics ICESat ATM Laser pointing, scattering, saturation Spatial/temporal cover (clouds) Basal uplift Changing snow-densification rates
GRACE: uncertainties Measurement errors Spill-over effects Atmosphere Basal uplift Greenland Small (few Gt a-1) Very Small + ~12 Gt a-1 Antarctica *V & W # R et al + ~13 Gt a-1 + ~9 Gt a-1 + ~72 Gt a-1* + ~25 Gt a-1 # Low-resolution results refer to entire ice sheets, but are seriously limited by short temporal coverage
Greenland Ice Sheet: rates of surface-elevation change (d. S/dt) Above (red), and below (blue) ~ 2000 -m elevation
Greenland Mass Balance
ERS wavefront over Jakobshavn
Antarctic Surface Elevation Change LIS FRIS AP PIG RIS
Crane Glacier after Larsen breakup airborne lidar profiles measured in 2002 & 2004
Recent mass-balance of Greenland Antarctica Area (M km 2) 1. 7 12. 3 Volume (M km 3)* 2. 9 (7 m SLE) 24. 7 (57 m SLE) Total accumuln. (Gt a-1)# 500 (1. 4 mm SLE) 1850 (5. 1 mm SLE) Mass Balance Since ~1990: Thickening above 2000 m, at an accelerating rate; thinning at lower elevations, also accelerating to cause a net loss from the ice sheet of perhaps > 100 Gt a-1 Since early 1990 s: slow thickening in central regions and southern Antarctic Peninsula; localized thinning at accelerating rates of glaciers in Antarctic Peninsula and Amundsen Sea region. Probable net loss, but
Causes o o o post-glacial memory variability/trends in snowfall/melting changes in glacier velocities ice shelves basal lubrication ? ?
Sea-level change and the cryosphere, June 2006 QUESTION ACTION -How long will glacier acceleration continue, resulting from existing perturbations? - Extend time series of observations - Model development and comparison with truth Relative importance of ice-shelf weakening and melt-water lubrication? - As above plus field measurements East Antarctica: is this also vulnerable to “perturbation weakening”? - Remote-sensing surveys, and time series to identify current status - Why are ice shelves thinning? - Ocean measurements near/beneath ice shelves - Model development and comparison with truth - Possible causes for ice-shelf breakup? - Field observations and modeling Importance of oscillations and trends in surface accumulation? - Ice cores, accumulation radar, and modeling Quantify the impact of changes in summer melt rates? - AWS, field work including percolation, and modeling - Relationship to the “Big Picture”: the link to prescribed scenarios of future climate change - Climate-warming scenarios must include parameters important to the ice sheets: accumulation; summer temperatures; ocean conditions near ice sheets and beneath ice shelves
- Slides: 23