Observed Changes in Particle Abundance Driven by Changes in the Diel Thermocline

Marine snow formation and settling is a key part of the oceans carbon cycle. A detailed understanding of those processes is important to our understanding of CO₂ sequestration into the deep ocean, and the influence that atmospheric greenhouse gasses have on the global carbon cycle and ocean acidification. In the Gulf of Mexico (GoM), natural marine snow and marine snow associated with the Deepwater Horizon oil spill have, in previous studies, been identified as the main contributor of removing the spilled oil from the water column to the sediments. This study evaluates existing data, collected in the northern GoM, to develop a deeper understanding of marine snow settling processes. Data from five years of cruises in the GoM has been compiled to examine daily, seasonal, and annual trends of marine snow abundance. Here, we report high resolution time series data to describe the processes and the depths at which variations in physical properties of the water column allow the settling of marine snow particles out of the turbulent mixed later into the deeper water column. Images of particle abundance from a marine snow profiling camera were analyzed to examine the overall size specific distribution of particles with depth, and over time. CTD data, obtained alongside the camera system and using ships CTD rosette, are analyzed for changes in density, temperature, salinity, fluorescence, and oxygen with depth. Specifically the upper 250 m of the water column are studied at one-meter intervals, due to large variations of these properties with changes in depth. Preliminary results suggest that particles potentially escape the mixed layer through diel heating and cooling cycles, causing variations in the depth of the diel thermocline. Particles isolated below the diel thermocline during these cycles, can potentially settle and thus contribute to the export of material from the surface ocean. Our goal is now to figure out how much marine snow is being introduced into the layer below the thermocline.