HOE Legacy 2B Particle Number Flux

Résumé fourni par la source

This dataset consists of measurements of particle flux taken during the SCOPE Hawaii Ocean Experiment - Legacy 2B (HOE Legacy 2B) cruise in in July and August 2015 at Station ALOHA. The size spectrum of sinking particle flux was microscopically examined using Particle Interceptor Traps (PITs) containing polyacrylamide gels (Ebersbach and Trull 2008, McDonnell and Buesseler 2012, McDonnell et al. 2015). Free-drifting sediment trap arrays containing 12 PITs (cross sectional area of 0.0039 m2) at each of 4 discrete depths (150, 300, 500, 750 m) were deployed. Two PITs at each depth were deployed with polyacrylamide gels mounted to the base of the traps; the remaining traps were used for subsequent analyses of particulate carbon and nitrogen (PC/PN) fluxes. Traps containing gels were prepared as described in Durkin et al. (2015) using custom-built 7.6 cm diameter polycarbonate cups as the base for each trap. A total of 100 mL of the gel solution was poured into each cup, yielding a solidified gel that was ~2.5 cm in height. Gel cups were covered and stored refrigerated until deployment. During deployment, cups containing the solidified gels were affixed to the bottom of the PITs, and traps were gently filled with a 0.5 mm filtered brine-fixative seawater solution (50 g NaCl L-1 and 1% formalin final concentration). Duplicate gel cups were left in the refrigerator to serve as analytical blanks. Upon recovery, gel traps were placed in the dark and allowed to settle for 8 hours prior to processing. The brine-fixative solution was aspirated from each gel trap and cups were removed, stored in covered containers and refrigerated until laboratory analyses. Approximately 1 month after recovery, in the shore-based laboratory, gel-embedded particles were visualized and imaged using Nikon SMZ1500 stereomicroscope equipped with a Nikon DS Fi1 color camera and fiber optic light source. A grid (5 x 5 mm squares) was placed under each gel and the entire gel was photographed at 20x and 40x magnification. Vertical heterogeneity in the distribution of particles within the gels occasionally required capturing multiple images in each field of view from differing focal planes. The resulting images were analyzed using ImageJ software, and converted to binary images for subsequent particle sizing (Durkin et al. 2015). At the 40x magnification, particles <10 mm could not be accurately identified. We calculated the equivalent spherical diameter (ESD) based on the two-dimensional surface area calculated for each particle. Using the derived ESD, particles were classified into 10 logarithmically spaced size bins ranging from 10 μm to 1653 μm. The resulting particle size distribution was calculated from the number of particles in each size bin, normalized to the width of each size bin, and the duration of deployment. Particle counts from the duplicate gels deployed at each depth were averaged and analytical blanks were subtracted.

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