Optical Survey of Transparent Marine Particles <1mm Including Gels from the Azores to the Canary Islands

Using a new shadowgraph imaging system we have demonstrated that particle numbers in the ocean are orders of magnitude higher than reported by conventional imaging systems largely due to the abundance of transparent particles such as gels. Here we report the results of a particle study from a North Atlantic expedition ranging from the Azores to the Canary Islands. Transparent particles (captured at high sensitivity) decreased in numbers with depth similar to denser particles (recorded at lower sensitivity). However, the proportion of transparent to denser particles consistently increased in the lower mesopelagic and upper bathypelagic zones, specifically between 500 and 1500 m depth. The proportion of transparent to denser particles decreased again in the bathypelagic layer below 1500m depth with some notable exceptions. These distributional shifts may be linked to water mass characteristics and the greater degree of decay of particles that had sunk from the surface into the meso- and bathypelagic layers.