Small-Scale Salinity Variability from Thermosalinographs: A Global Perspective

Fronts, eddies, filaments, upwelling, and freshwater input from rainfall, rivers, and ice-melt can all generate submesoscale to mesoscale variations in sea surface salinity. Knowledge about the horizontal variability of surface salinity is valuable for understanding ocean surface dynamical processes. Salinity variability at these scales also has implications for validation of satellite-based salinity measurements, as satellite radiometers average over a spatial footprint ~50-100 km across whereas the most commonly used data for comparison with the satellite values are the point measurements provided by Argo profilers. In this study, we use near-global measurements from shipboard thermosalinographs (TSGs) to characterize salinity variability over spatial scales ranging from a few kilometers to the scale of the satellite footprints. Regions characterized by strong currents, or containing fronts, river outflow, or ice-melt, are found to have particularly energetic small-scale salinity variations. Interestingly, rainy regions do not show elevated salinity variability, likely because TSGs are typically located at 5-m depth whereas rain-induced fresh anomalies are often trapped in a shallower layer. We use the TSG observations to explore the impacts of small-scale salinity variations on interpretation and validation of satellite-based salinity measurements. We also present a global analysis of the wavenumber spectra of near-surface salinity from the TSG measurements.