Combining Observations, Remote Sensing, and Hydrodynamic Modeling to Assess the Impact of Atmospheric and Tidal Fronts on Coastal Bio-Optical Variability

Sub-mesoscale (0.1 – 10 km) fronts and filaments are ubiquitous features in coastal regions and their importance in coupled ocean-atmosphere processes has been recognized, yet measurements of their dynamics are rare. The goal of the Integrated Coastal Bio-Optical Dynamics (ICoBOD) project is to combine in situ measurements, remote sensing imagery, and hydrodynamic modeling to assess the impact of two key forcing processes, atmospheric and tidal fronts, on fine-scale bio-optical and physical variability in a shallow, dynamic, coastal environment. During a 25-day field experiment in March/April 2018, we deployed eight moorings to collect a time series of physical and bio-optical measurements near a convergence zone in Mississippi Sound (northern Gulf of Mexico). The sampling encompassed a spring/neap tidal cycle and the passage of four atmospheric cold fronts. For a one-week period in the middle of the mooring deployment, we conducted ship surveys and coincident aircraft and UAV overflights with thermal and hyperspectral ocean color imagers. The aircraft overflew the study area, located suitable “color” fronts, and directed the ship to the fronts. We released two different color fluorescent dyes (rhodamine, red; uranine, green) on opposite sides of a front to facilitate visualization of advection/mixing/dispersion processes. High-resolution (50 m) hydrodynamic model simulations provided 3-dimensional temperature, salinity, and current fields, as well as derived frontal characteristics (strain, divergence, curl), across the model domain, and are aiding interpretation of the frontal dynamics. Here, we focus on the temporal/spatial bio-optical variability as related to the physical properties.