No abstract

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...

The upper ocean, including the biologically productive euphotic zone and the mixed layer, has great relevance for studies of physical, biogeochemical, and ecosystem processes and their interaction. Observing this layer with a continuous presence, sampling many of the relevant variables, and with sufficient vertical resolution, has remained a challenge. Here a system is presented that can be deployed on the top of deep-ocean moorings, with a drive mechanism at depths of 150-200 m, which mechanically winches a large sensor float and smaller communications float tethered above it to the surface and back down again, typically twice per day for periods up to 1 year. The sensor float can carry several sizeable sensors, and it has enough buoyancy to reach the near surface and for the communications float to pierce the surface even in the presence of strong currents. The system can survive mooring blowover to 1000-m depth. The battery-powered design is made possible by using a balanced energy-conserving principle. Reliability is enhanced with a drive assembly that employs a single rotating part that has no slip rings or rotating seals. The profiling bodies can break the surface to sample the near-surface layer and to establish satellite communication for data relay or reception of new commands. An inductive pass-through mode allows communication with other mooring components throughout the water column beneath the system. A number of successful demonstration deployments have been completed.