AS THE RESOLUTION OF OBSERVATIONS AND MODELS IMPROVES EMERGING EVIDENCE INDICATES THAT OCEAN VARIABILITY ON SPATIAL SCALES OF O(1) KM (I.E. THE SUBMESOSCALE) IS OF FUNDAMENTAL IMPORTANCE TO OCEAN CIRCULATION AIR-SEA INTERACTION AND BIOGEOCHEMICAL CYCLING. OUR RECENT WORK HAS SHOWN THAT IN MANY REGIONS SALINITY VARIABILITY DOMINATES OVER TEMPERATURE VARIABILITY IN FORMING SUBMESOSCALE [AND MESOSCALE O(10-100 KM)] DENSITY FRONTS. THE OVERARCHING MOTIVATION OF THE PROPOSED WORK IS THE NEED TO BETTER CHARACTERIZE SURFACE DENSITY VARIABILITY AND IN PARTICULAR THE ROLE OF SALINITY ACROSS THE SUBMESOSCALE TO MESOSCALE RANGE [THE "(SUB)MESOSCALE"]. CURRENT SATELLITE TECHNOLOGY DOES NOT ALLOW FOR THE OBSERVATION OF SUBMESOSCALE FEATURES IN SEA SURFACE SALINITY (SSS). HOWEVER SUBMESOSCALE VARIABILITY CAN BE DETECTED IN SATELLITE MEASUREMENTS OF SEA SURFACE TEMPERATURE (SST) AND OCEAN COLOR (OC). WE PROPOSE AN IN-DEPTH STUDY OF (SUB)MESOSCALE OCEAN VARIABILITY USING A COMBINATION OF SATELLITE (SSS OC SST) AND IN SITU (SALINITY TEMPERATURE OPTICAL PROPERTIES AND VELOCITY) OBSERVATIONS. WE WILL QUANTIFY THE STRUCTURE AND KINEMATIC PROPERTIES OF SALINITY AND DENSITY FRONTS ON SCALES FROM 1 TO 100 KM IN TWO REGIONS OF STRONG (SUB)MESOSCALE SALINITY VARIABILITY: THE CALIFORNIA CURRENT FRONT (CCF) AND THE GULF STREAM/NORTH ATLANTIC DRIFT FRONT (GSF). THESE REGIONS ARE RICH IN (SUB)MESOSCALE SALINITY STRUCTURE AND THEY WILL SERVE AS "LABORATORIES" FOR QUANTIFYING AND CHARACTERIZING (SUB)MESOSCALE SSS DYNAMICS. THE SURFACE AND SUBSURFACE (SUB)MESOSCALE DYNAMICS IN THE CCF WILL BE CHARACTERIZED BY CARRYING OUT LOW-COST FLEXIBLE FIELD EXPERIMENTS WITH A SMALL-VESSEL EQUIPPED WITH AN UNDERWAY CTD/OPTICS/ACOUSTICS PACKAGE. IN THE NORTH ATLANTIC WE WILL LEVERAGE OUR INVOLVEMENT IN THE NASA-FUNDED NORTH ATLANTIC AEROSOLS AND MARINE ECOSYSTEMS STUDY (NAAMES) TO CONDUCT UNDERWAY CTD AND ACOUSTIC SURVEYS OF MULTIPLE MESOSCALE EDDIES AND SUBMESOSCALE FRONTS. WE WILL COMBINE THE IN SITU OBSERVATIONS WITH SATELLITE SST SSS AND OC OBSERVATIONS AS WELL AS EXISTING GLIDER DATA FROM THE OCEAN OBSERVATORIES INITIATIVE (OOI). BY EXPLOITING SATELLITE OBSERVATIONS WE WILL DEVELOP STATISTICAL CHARACTERIZATIONS OF (SUB)MESOSCALE SALINITY VARIABILITY AND ITS RELATIONSHIP TO SSS MEASUREMENTS FROM THE SMAP MISSION. THE OUTCOME OF THE PROPOSED WORK IS IMPROVED UNDERSTANDING OF SUBMESOSCALE/MESOSCALE INTERACTIONS IN REGIONS WHERE SALINITY DRIVES DENSITY VARIABILITY ON THESE SCALES. THE PROJECT FITS INTO THE OBJECTIVES OF NASA'S OSST THROUGH MAKING SYNERGISTIC USE OF NASA SSS MEASUREMENTS WITH OTHER SATELLITE AND IN SITU MEASUREMENTS.