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Published byMelina Goodwin Modified over 8 years ago
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Polar Ice Sheets and Ice Shelves: Mass Balance, Uncertainties, and Potential Improvements Robert H Thomas…etc
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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
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Mass budget: uncertainties AntarcticaGreenland (Gt a -1 ) Snowfall+ 130 (7%)+ 25 (5%) Ice flow+ 93 (5%)+ 25 (5%) Melt runoffVery small+ 30 (10%) Mass balance (mm/yr SLE) + 160 (+ 0.5) + 46 (+ 0.15)
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Altimetry: uncertainties SRALTICESatATM Topography effects Laser pointing, scattering, saturation Changing dielectrics Spatial/temporal cover (clouds) Basal uplift Changing snow-densification rates
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GRACE: uncertainties Measurement errors Spill-over effects AtmosphereBasal uplift GreenlandSmall (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
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Greenland Ice Sheet: rates of surface-elevation change (dS/dt) Above (red), and below (blue) ~ 2000-m elevation
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Greenland Mass Balance
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ERS wavefront over Jakobshavn
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Antarctic Surface Elevation Change PIG AP LIS RIS FRIS
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Crane Glacier after Larsen breakup airborne lidar profiles measured in 2002 & 2004
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Recent mass-balance of Greenland and Antarctica. GreenlandAntarctica Area (M km 2 ) 1.712.3 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 BalanceSince ~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 after 2000. Since early 1990s: 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 close to balance.
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Causes opost-glacial memory ovariability/trends in snowfall/melting ochanges in glacier velocities -ice shelves -basal lubrication -????
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Sea-level change and the cryosphere, June 2006 QUESTIONACTION -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
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