Diurnal Periodicity in Particle Flux in the Gulf of Mexico, Estimates from Flux Camera observed Particle Data

To estimate a diurnal periodicity in the biological pump of marine snow particles from the surface mixed layer into the deep ocean, a drifting surface tethered floating array was deployed at five sites in the northern Gulf of Mexico in June 2017. This array included a marine snow flux camera system at 150 m depth which was used to image particles at a 40 second interval for 24 to 30 hour periods. Images obtained by this camera system, were processed using the Image Pro Software, to identify and measure all particles within a well defined volume of water, to determine the equivalent spherical diameter, an estimated volume, and a settling speed for each particle. Using these parameters, particle mass was estimated using algebraically rearranged calculations for settling speed. Peaks of significantly increased particle counts were detected at each site with a defined baseline outside of these peaks, with particle diameters not following this pattern. Most of these peaks occurred at noon local time, with one site having its peak at midnight. More than 70% of the total mass flux, calculated using in-situ measured settling speeds, was contained within these peaks. Relative currents, measured at the flux camera depth, did not correlate with the mass flux. Data from CTD casts, performed near the floating array while it was deployed, revealed a minimum change in diel thermocline depths of 7 m at all sites. We conclude that the variations in thermocline depth, isolated particles below the thermocline, thus allowing this material to escape the mixed layer, ultimately contributing to the vertical export.