OBJECTIVE: ANTARCTIC SEA ICE EXTENT (SIE) HAS EXPERIENCED A SMALL BUT SIGNIFICANT POSITIVE TREND OVER THE ERA FOR WHICH MEASUREMENTS OF SEA ICE CONCENTRATION ARE AVAILABLE (1979-PRESENT). THIS TREND IS CONTRARY TO MOST GLOBAL INDICATORS OF ICE EXTENT AND MASS CHANGE AND IS ALSO CONTRARY TO PREDICTIONS BY COUPLED CLIMATE MODELS. THE POSITION OF THE EDGE OF THE ICE PACK SHOWS VARIABILITY RELATED TO OCEAN EDDIES GENERATED BY UNSTABLE FLOW OF THE ANTARCTIC CIRCUMPOLAR CURRENT (ACC). THIS EDDY-SCALE VARIABILITY IN THE SEA ICE POINTS TO INTERACTIONS BETWEEN THE EDDIES AND THE ICE THAT MAY PLAY A SIGNIFICANT ROLE IN SETTING SIE AND THE RATE AT WHICH SEA ICE MASS IS LOST AT THE ICE EDGE. OUR OBJECTIVES ARE TO: (1) DOCUMENT THE REGIONAL AND INTERANNUAL VARIABILITY OF THE EDDY CONTRIBUTION TO ICE EDGE POSITION; (2) RELATE THESE STATISTICS TO KNOWN MODES OF GLOBAL CLIMATE VARIABILITY; (3) UNDERSTAND AND QUANTIFY THE PHYSICS OF EDDY/ICE INTERACTIONS INCLUDING OCEAN/ICE STRESSES AND HEAT FLUXES TO DETERMINE THE ROLE OF EDDIES IN SEA-ICE MASS BALANCE; AND (4) USE THIS KNOWLEDGE TO PREDICT CHANGES IN THE ROLE OF EDDIES FOR PROJECTED FUTURE STATES OF THE SOUTHERN OCEAN. METHODS&TECHNIQUES: WE WILL ANALYZE SATELLITE-DERIVED SEA ICE CONCENTRATION FROM A VARIETY OF PASSIVE MICROWAVE SENSORS (SSM/I AMSR-E AND AMSR-2) TO QUANTIFY THE EDDY CONTRIBUTION TO ICE-EDGE POSITION. THESE ANALYSES WILL BE PERFORMED ON DAILY SATELLITE DATA FOR AUSTRAL WINTER PERIODS (MAY-NOVEMBER INCLUSIVE) WHEN THE ANTARCTIC SEA-ICE PACK IS EXTENSIVE AND THE ICE EDGE IS CLEARLY DEFINED. THE STATISTICS OF THE EDDY CONTRIBUTION INCLUDING TYPICAL SPATIAL SCALES AND EDDY PROPAGATION SPEEDS WILL BE ANALYZED BY REGIONS RELATED TO DIFFERENT LARGE-SCALE CONTROLS OF ICE FRONT POSITION INCLUDING MAJOR ACC FRONTS AND UNDERLYING BATHYMETRY. THE INTERANNUAL VARIABILITY OF THESE STATISTICS WILL THEN BE CORRELATED WITH MAJOR CLIMATE MODES INCLUDING ENSO AND THE SOUTHERN ANNULAR MODE. WE WILL ANALYZE OUTPUT FROM THREE EXISTING COUPLED OCEAN/SEA-ICE MODELS INCLUDING THE NASA-FUNDED ECCO-V4R3. WE WILL USE OUTPUT FROM A HIGH-RESOLUTION EDDY-RESOLVING MODEL TO INVESTIGATE THE PHYSICS OF EDDY/ICE INTERACTIONS INCLUDING DYNAMIC CONTROLS (ADVECTION BY STRESS FROM EDDY VELOCITIES) AND THE THERMODYNAMIC MECHANISMS FOR AND MAGNITUDES OF HEAT AND FRESHWATER EXCHANGES BETWEEN THE OCEAN AND ICE NEAR THE ICE EDGE. THESE RESULTS WILL BE COMPARED WITH OCEAN/ICE INTERACTIONS IN TWO OTHER OCEAN STATE ESTIMATE MODELS ONE THAT PARTIALLY RESOLVES EDDY PERTURBATIONS IN THE SEA ICE AND ANOTHER COARSER-RESOLUTION MODEL WHICH DOES NOT. THE RESULTS FROM ANALYSES OF THE HIGH-RESOLUTION MODEL WILL IDENTIFY WHETHER EDDY/ICE INTERACTIONS ARE SIGNIFICANT TO LARGE-SCALE ANTARCTIC SEA ICE PROPERTIES AND THE UPPER OCEAN. COMPARISON OF HIGH- AND LOWER-RESOLUTION MODELS WILL INFORM THE DIRECTION OF FUTURE DEVELOPMENT OF CLIMATE MODELS AND APPROACHES THAT MIGHT BE TAKEN TO PARAMETERIZE UNDER-RESOLVED PROCESSES CONTROLLING THE EXTENT AND MASS BUDGET OF THE ANTARCTIC SEA-ICE PACK. SIGNIFICANCE: THE STUDY ADDRESSES PROCESSES AFFECTING THE MASS BALANCE AND EXTENT OF THE ANTARCTIC ICE PACK WHICH PLAYS A SIGNIFICANT ROLE AS AN INSULATOR BETWEEN THE HIGH-LATITUDE OCEAN AND ATMOSPHERE REDUCING SOLAR RADIATION INPUT AND GAS EXCHANGE AND ACTING AS A MEDIUM FOR TRANSPORT OF FRESHWATER NORTHWARDS FROM ANTARCTIC MARGINS. THE STUDY ADDRESSES CLIVAR S NEED FOR BETTER UNDERSTANDING AND MODELING OF CLIMATE CHANGE IN POLAR REGIONS AND ITS GLOBAL IMPACT. OUR WORK WILL IDENTIFY STRENGTHS AND WEAKNESSES OF THE CURRENT GENERATION OF THE NASA-FUNDED ECCO OCEAN STATE MODEL TOWARDS MOTIVATING FUTURE IMPROVEMENTS IN THIS VALUABLE COMMUNITY RESOURCE. IN ADDITION THE PROJECT WILL LAY GROUNDWORK FOR UTILIZING SEA-ICE FREEBOARD SEA-SURFACE HEIGHT AND ICE SHEET AND ICE SHELF SURFACE HEIGHT CHANGE OBSERVATIONS FROM NASA S ICESAT-2 LASER ALTIMETER SATELLITE WHICH IS SCHEDULED TO LAUNCH IN AUTUMN 2018.