Episodic Particle Export Revealed by Combining Imaging and Optics, including the First Deployment of an Open-Faced Flux Camera ("SnoCam")

Episodic particle export is difficult to resolve with conventional sampling methods, and storms further constrain ship-based observations. Here we present observations from the first deployment of a SnoCam, a low-cost, upward-facing ‘flux camera’ deployed on a Lagrangian float during the EXPORTS (EXport Processes in the Ocean from RemoTe Sensing) North Atlantic campaign. Ship-board activities were interrupted by a series of intense storms and so only the autonomous vehicles were able to obtain an uninterrupted record over the entire 21 day occupation. The float-attached SnoCam was combined with a co-located optical sediment trap, and was able to resolve multiple particle flux pulses (dominated by particles > 1 mm) coinciding with storm events. Combining SnoCam area fluxes with matched imaged particle size distribution (PSD) cross-sectional densities yielded estimated population-mean sinking speeds of 30.8 ± 28.3 m d -1 for large particles and 5.8 ± 4.4 m d -1 for small particles. Comparisons between optical backscattering and imaged PSD observations showed concurrent increases in particle concentrations near the base of the mixed layer, followed by their extension to greater depths. The short flux pulses occurred within a broader period of enhanced export captured by a particle-intercepting sediment trap array spanning the upper 500 m. Together, these observations place the two shallow flux pulses within a broader period of enhanced export into the mesopelagic, and demonstrate how sustained autonomous observations can resolve episodic export variability and identify the particle size classes and types responsible.