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Volume distribution for particles between 3.5 to 2000 μm in the upper 200 m region of the South Pacific Gyre
1Laboratoire d'Océanographie de Villefranche (LOV), Observatoire Océanologique, BP 28, 06234 Villefranche sur mer Cedex, France
2Université Pierre et Marie Curie-Paris 6, UMR 7093, 06234 Villefranche sur Mer, France
3Plymouth Marine Laboratory, Prospect Place, Plymouth, PL1 3DH, USA
4Department of Oceanography, Texas A&M University, College Station, TX 77843, USA
Abstract. The French JGOFS BIOSOPE cruise crossed the South Pacific Gyre (SPG) on a transect between the Marquesas Islands and the Chilean coast on a 7500 km transect (8° S–34° S and 8° W–72° W). The number and volume distributions of small (3.5<d<30 μm) and large particles (d>100 μm) were analysed combining two instruments, the HIAC/Royco Counter (for the small particles) and the Underwater Video Profiler (UVP, for the large particles). For the HIAC analysis, samples were collected from 12 L CTD Rosette bottles and immediately analysed on board while the UVP provided an estimate of in situ particle concentrations and size in a continuous profile. Out of 76 continuous UVP and 117 discrete HIAC vertical profiles, 25 had both sets of measurements, mostly at a site close to the Marquesas Islands (site MAR) and one in the center of the gyre (site GYR). At GYR, the particle number spectra from few μm to few mm were fit with power relationships having slopes close to −4. At MAR, the high abundance of large objects, probably living organisms, created a shift in the full size spectra of particles such as a single slope was not appropriate. The small particle pool at both sites showed a diel pattern while the large did not, implying that the movement of mass toward the large particles does not take place at daily scale in the SPG area. Despite the relatively simple nature of the number spectra, the volume spectra was more variable because what were small deviations from the straight line in a log-log plot were large variations in the volume estimates. Results showed that the volume of large particles can equal the volume of the smaller particles. However the proportion of material in large particles decreased from the mesotrophic conditions at the border of the SPG to the ultra-oligotrophy of the center in the upper 200 m depth. We expect large particles to play a major role in the trophic interaction in the upper waters of the South Pacific Gyre.
Discussion Paper (PDF, 1085 KB) Interactive Discussion (Closed, 6 Comments) Final Revised Paper (BG)
Citation: Stemmann, L., Eloire, D., Sciandra, A., Jackson, G. A., Guidi, L., Picheral, M., and Gorsky, G.: Volume distribution for particles between 3.5 to 2000 μm in the upper 200 m region of the South Pacific Gyre, Biogeosciences Discuss., 4, 3377-3407, 2007. Bibtex EndNote Reference Manager
