A high resolution camera system (ParCa) for imaging particles in the ocean: System design and results from profiles and a three-month deployment
Abstract:For direct optical measurement of abundance, concentration and size distribution of marine particles, a high-resolution camera system (ParCa) was designed to improve on similar systems used by Honjo et al. (1984), Asper (1987) and others. Imaging a probe volume of up to 37 1, smallest particles with diameters of 50 μm can be counted. The images provide information on particle size, shape and abundance either during profiling through the water column or while moored in a certain depth over time. Depth profiles were acquired between fall 1992 and late spring 1993 on R. V. Meteor cruises M22-1 and M23-3 at 6 stations in the equatorial Atlantic Ocean and off the west African shelf. The images show variable particle and aggregate concentrations through 550 m of the water column, with highest concentrations in the upper 80 m. A distinctive change in the depth of the upper chlorophyll maximum from about 75 m in the Brazil Basin to about 50 m in the Guinea Basin was measured with the attached INFLUX current meter (Krause and Ohm, 1996) and is as well represented in the particle abundances maximum of two selected profiles. In contrast, both profiles show a second particle abundance maximum between 100 and 250 m, which is not visible in the chlorophyll-α and backscatter signal of the INFLUX sensors. Total particle abundance maxima raise from 677 counts per liter in the central Brazil Basin to 991 counts in the Guinea Basin, corresponding to marine snow abundances of 57 and 127 counts per liter, respectively.
In order to compare high-resolution data on particle concentration and flux through time, ParCa was also deployed on a sediment-trap mooring at 995 m depth in the Canary Basin between June and September 1994. First results show similar trends in sediment-trap derived fluxes of particulate matter from 2.8 to 67.2 mg m−2 d−1 and equivalent spherical volumes of particles with diameters >0.5 mm from 0.98 to 4.13 mm3 l−1.
Document Type: Research Article
Publication date: 1996-05-01
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