Design and application of a semi-automated filtration system to study the distribution of particulate organic carbon in the water column of a coastal upwelling system

The processes controlling the production, transport and ultimate fate of particulate organic carbon (POC) in marine systems play a major role in the global carbon cycle. Direct measurements of POC concentrations in oceanic waters have been used extensively to investigate these processes, but because of the time-intensive effort associated with manual collection and filtration of water samples, this approach often results in limited temporal or spatial coverage. To increase the frequency of POC measurements, we designed and built a semi-automated filtration system (SAFS) that can be linked to a ship's underway surface water flow system and/or a towed profiling vehicle with pumping capabilities. Our results show that, compared to manual filtration, SAFS provides the ability to easily perform filtrations at high enough frequency to measure POC concentrations at spatial and temporal resolutions that are closer to those possible with in situ sensors. When combined with optical measurements, SAFS allows for the characterization of several distinct pools of particles within different geographical and depth regions of the water column off the Oregon Coast. These initial applications yielded data that provide considerable insight into the sources and character of particles in the water column and prove that this approach can be used to gain valuable information on the biogeochemistry of this and other similar ocean margins.