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We combined a Sounding Oceanographic Lagrangian Observer float with a Laser Optical Plankton Counter (LOPC) and a fluorometer to make an autonomous biological profiler, the SOLOPC. The instrument senses plankton and other particles over a size range of 100 mm to 1 cm in profiles to 300 m in depth and sends data ashore via satellite. Objects sensed by the LOPC include aggregates and zooplankton, the larger of which can be distinguished from one another by their transparency. We hypothesized that the diel production of particles and their loss by sinking and grazing are reflected in the change of the particle distribution. We present data from four deployments of the SOLOPC off California. Particle volume was maximal at the base of the surface mixed layer and correlated with chlorophyll a fluorescence. In a 3-d deployment in 2005, particle volume was greatest in the early evening and smallest in the morning, and average particle size increased with depth. Eigenvector analysis of the particle volume distribution as a function of diameter for each of the deployments yielded size peaks characteristic of planktonic crustaceans. Ship-based measurements showed that the abundance of opaque particles of 1.1-1.7 mm equivalent spherical diameter was positively correlated with copepods of this size and simultaneously collected in nets. This relationship was used with SOLOPC data to estimate the distribution of large copepods, which were most abundant beneath the depth of maximal particle flux, estimated from particle size and published sinking rates. Our data are consistent with a model with diel production of particles and their loss by sinking and grazing.Plankton and other particles are key elements of marine ecosystems and biogeochemical cycles. The euphotic zone is dynamic, with highly variable rates of production and loss of particulate organic matter. New primary production and its export from the euphotic zone are mediated by processes that include mixing, migration, grazing, aggregation, and sinking. Significant variation of these processes occurs on the scale of hours (e.g., diel), days (e.g., events), months (e.g., seasons), and longer and in the vertical (e.g., layers) and horizontal (e.g., across fronts and between water masses). A challenge in oceanography is to measure features of assemblages of particles and plankton with sufficient accuracy, resolution, and regularity to describe their variation and understand their dynamics. We report here on our use of the SOLOPC, an autonomous, Lagrangian profiling float with a conductivity-temperature-depth instrument (CTD), optical particle counter, and fluorometer, to assess plankton and other particles in the upper 100 m off Southern California. Our results are consistent with the diel production of particles, by aggregation of phytoplankton, feces, and detrital material, and their loss by sinking and grazing.There is a clear need for measurements of plankton and other particles using autonomous, Lagrangian platforms and sensors, or ALPS (e.g., floats, gliders...

[1] We describe the development and testing of an autonomous device designed to revolutionize Earth structure determination via global seismic tomography by detecting earthquakes at teleseismic distances in the oceans. One prototype MERMAID, short for Mobile Earthquake Recording in Marine Areas by Independent Divers, was constructed and tested at sea. The instrument combines two readily available, relatively low-cost but state-of-the-art components: a Sounding Oceanographic Lagrangian Observer, or SOLO float, and an off-the-shelf hydrophone, with custom-built data logging hardware. We report on the development of efficient wavelet-based algorithms for the detection and discrimination of seismic events and analyze three time series of acoustic pressure collected at a depth of 700 m in pilot experiments conducted offshore San Diego, CA. In these tests, over 120 hours of data were gathered, and five earthquakes, of which one was teleseismic, were recorded and identified. Quantitative estimates based on these results suggest that instruments of the MERMAID type may collect up to a hundred tomographically useful teleseismic events per year. The final design will also incorporate a Global Positioning System receiver, onboard signal processing software optimized for low-power chips, and high-throughput satellite communication equipment for telemetered data transfer. With these improvements, we hope to realize our vision of a global array of autonomous floating sensors for whole-earth seismic tomography.

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