Marine snow particle area: size distribution in the NE Gulf of Mexico August 2010-August 2014
Description
Date (local and GMT), Time (local and GMT), Latitude (decimal degrees N), Longitude (decimal degrees W), Station, Depth of images (m), Volume filtered (m^3), Marine snow particle size (area mm2), Abundance (count/m^3). Files names are CruiseDate (Month/Year)_Station: WB0810_DSH08. SIPPER used a high speed Dalsa Piranha-2 line-scan camera and a pseudo-collimated LED generated light sheet to image the shadows and outlines of resolvable particles that passed through a 100 cm2 field of view. The operational optical resolution of the system is ~65 um. SIPPER was towed at speeds between 2-3 knots in an oblique profile through the water column, spending approximately equal amounts of time at each meter of depth between the surface and 300 m. At stations with a bottom depth shallower than 300 m, SIPPER was towed within approximately 5 m from the seafloor. Imaging and environmental data were stored internally on a Firewire hard drive and processed upon retrieval of the SIPPER instrument from a deployment using a customized software package called the Plankton Image Classification and Extraction Software (PICES). PICES was used to extract images of interest, classify them using user-specified training libraries and to manage the SIPPER images and environmental data collected. The particle size spectra show the size dependence of particles and follows the methods described in Jackson & Burd (1998) and Jackson & Checkley (2011). A normalized particle volume spectrum (nVd) was calculated, where n is particle abundance, V is particle volume, and d is the median particle diameter within each size bin. Pixel width of images was fixed, while pixel length took into account the flow rate and scan rate. The pixel area of each image was determined, and the equivalent spherical diameter (ESD) and volume (V) were calculated based on the optical cross-section. The ESD is defined as the diameter of a circle having the same area as the projected image of the particle (Billiones et al., 1999). Particle diameter (d) size bins ranged from 0.100 to 105.12 mm, where each bin size increased in a geometric progression by about 6% (bin size scale, k = 21/12) over the previous one, since the number of large particles is rare compared to the abundance of smaller sized particles. Normalizing the abundance data (n) to volume (V) gives more weight to larger sized particles. SIPPER Environmental Sensors. Environmental data were collected simultaneously with the SIPPER imaging system during each deployment. Sensors included a Seabird 19Plus CTD, Seabird SBE43 oxygen sensor, and WET Labs FLNTURTD chlorophyll fluorescence and turbidity, and a transmissometer. AWET Labs CDOM sensor also was used on a few cruises. Sensors were calibrated at Seabird and WET Labs and then integrated into the SIPPER towed platform.
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Funders
- Gulf of Mexico Research Initiative