THE ANTARCTIC ICE SHEET MASS BUDGET IS DOMINATED BY ACCUMULATION THROUGH SNOWFALL AND DYNAMIC LOSS TO THE OCEANS VIA THE GRAVITATIONALLY FORCED FLOW OF ICE STREAMS AND GLACIERS. ANTARCTICA IS CURRENTLY PROVIDING A SMALL CONTRIBUTION (~+0.2 MM/YEAR) TO TOTAL GLOBAL SEA LEVEL RISE OF ~+3.2 MM/YEAR. HOWEVER BASED ON PROJECTED CLIMATE CHANGE PALEO ANALOGS AND RECENT MODELING ITSCONTRIBUTION MAY INCREASE DRAMATICALLY BY LATER IN THE 21ST CENTURY.MOST MASS LOSS FROM THE ANTARCTIC ICE SHEET ULTIMATELY OCCURS FROM THE ICE SHELVES THE FLOATING EXTENSIONS OF INLAND GLACIERS AND ICE STREAMS. ICE SHELVES CAN ACT TO "BUTTRESS" LAND-ICE LOSS: RECENT OBSERVATIONS SHOW THAT REDUCTIONS IN EXTENT AND/OR THICKNESS OF AN ICESHELF CAN BE FOLLOWED BY ACCELERATION AND SURFACE DRAWDOWN OF THE ADJACENT GROUNDED GLACIERS AND ICE STREAMS INCREASING GLOBAL SEA LEVEL. CHANGING ICE SHELF EXTENT AND THICKNESS IMPACTS COASTAL ANTARCTIC CIRCULATION INCLUDING FLUXES OF FRESHWATER AND DENSE SHELF WATER THAT ARE SUBSEQUENTLY DISTRIBUTED TO THE BROADER SOUTHERN OCEAN AND BEYOND. ICE SHELF VARIABILITY THEREFORE HAS AFFECTS SEA-LEVEL RISE SOUTHERN HEMISPHERE SEA ICE THE OCEAN CONVEYOR BELT THE GLOBAL CLIMATE SYSTEM AND ANTARCTIC ECOSYSTEMS. ICE SHELVES ARE ALSO SENSITIVE INDICATORS OF CHANGES IN OCEANIC AND ATMOSPHERIC FORCING ACTING ON MARINE-TERMINATING GLACIER AND ICE-STREAM SYSTEMS. WITHTHESE INFLUENCES IN MIND THE GOALS OF OUR PROPOSED STUDIES ARE AS FOLLOWS:PRIMARY PROJECT GOALS: DEVELOP A DETAILED HISTORY OF ANTARCTIC ICE SHELF MASS AND STRESS CHANGES ON SEASONAL-TO-INTERANNUAL TIME SCALES AND SMALL SPATIAL SCALES; IMPROVE OUR UNDERSTANDING OF THE ENVIRONMENTAL PROCESSES THAT CAUSE THESE CHANGES; AND ASSESS WHETHER PROXIES FOR VARIABILITY OF THE ICE SHELF MASS BUDGET CAN BE OBTAINED FROM COARSE-GRID GLOBAL CLIMATE MODELS (GCMS).OUR MAIN DATA SOURCES FOR THIS STUDY ARE: ICESAT-1 LASER ALTIMETER DATA (2003-2009); OPERATION ICEBRIDGE (OIB) AIRBORNE LASER ALTIMETER AND RADIO ECHO SOUNDING (RES) ICE THICKNESS DATA (2009-PRESENT); CRYOSAT-2 RADAR ALTIMETER (RA) DATA (2010-PRESENT); AND EUROPEAN SPACE AGENCY (ESA) RA SATELLITES ERS-1 ERS-2 AND ENVISAT (1992-2012). THESE WILL BE AUGMENTED WITH GEOSAT (1985-1989) MODIS VISIBLE IMAGERY SSM/I AND AMSR-E SEA ICE CONCENTRATIONS ATMOSPHERE AND OCEAN REANALYSIS MODELS GCMS AND AS REQUIRED EXISTING IN SITU DATA SETS SUCH AS ICE-SHELF GPS AND OCEAN HYDROGRAPHY AND VELOCITY RECORDS.WE PROPOSE THE FOLLOWING CLOSELY INTER-RELATED ACTIVITIES.1) DEVELOP ACCURATE CONTINUOUS AND HIGH-RESOLUTION (IN SPACE X AND TIME T) RECORDS OF SURFACE ELEVATION H(X T) FOR ALL ANTARCTIC ICE SHELVES FROM 1992 TO NEAR THE END OF THE PROPOSED RESEARCH IN 2016 INCLUDING SEEKING METHODS FOR HETEROGENEOUS MULTI-SATELLITE ALTIMETER DATA INTEGRATION.2) INVESTIGATE WHETHER OBSERVATIONS OF FINE-SCALE ICE SHELF TOPOGRAPHIC FEATURES CAN IMPROVE OUR UNDERSTANDING OF CHANGES IN SPECIFIC MASS BALANCE TERMS AND STRESS FIELDS. FOR THIS ACTIVITY WE WILL FOCUS ON TWO ICE SHELVES REPRESENTING LIMITS OF CURRENT ICE SHELF STATE; ONELARGE AND PRESENTLY STABLE AND ONE SMALLER AND CURRENTLY THINNING RAPIDLY.3) RELATE OBSERVED VARIABILITY OF H(X T) ICE SHELF MASS BALANCE TERMS AND FINE-SCALE TOPOGRAPHY TO CHANGES IN THE OCEAN AND ATMOSPHERE RESOLVED BY GLOBAL CLIMATE MODELS (GCMS).WE WILL ALSO SUPPORT COLLEAGUES' ANALYSES OF GREENLAND ICE SHELVES WHICH ALTHOUGH RELATIVELY FEW AND SMALL MAY PLAY SIGNIFICANT ROLES IN THE RESPONSE OF THE NORTHERN GREENLAND ICE SHEET TO OCEAN CHANGE.THE PROPOSED WORK DIRECTLY ADDRESSES THE PROGRAM GOALS DESCRIBED IN THE 2012 NASA ROSES CALL FOR A.49 STUDIES WITH ICESAT AND CRYOSAT 2 AND NASA'S STRATEGIC GOAL 2 OBJECTIVE 2.1.5 TO "IMPROVE UNDERSTANDING OF THE ROLES OF THE OCEAN ATMOSPHERE LAND AND ICE IN THE CLIMATE SYSTEM AND IMPROVE PREDICTIVE CAPABILITY FOR ITS FUTURE EVOLUTION".