Field and laboratory studies on the effect of particle size and composition on optical backscattering measurements in hydrothermal plumes |
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| Institution: | 1. GRECO, Institute of Aquatic Ecology, University of Girona, Campus Montilivi, Faculty of Sciences, E-17071 Girona, Spain;2. Biology Centre of the Czech Academy of Sciences, Institute of Hydrobiology, ?eské Budějovice, Czech Republic |
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| Abstract: | We describe the performance of an inexpensive but highly sensitive light backscattering sensor (LBSS) suitable for use in deep-sea waters, where particle concentrations are typically <～0.1 mg/l. Laboratory calibrations using aluminosilicate particles and latex spheres show that the concentration-normalized backscattering of the LBSS, Kbs, is greatest for particles with a diameter close to the wavelength of light emitted by the LBSS (0.88 μm), declining by more than a factor of five for particles <0.1 μm or >10 μm. Field studies indicate that in hydrothermal plumes dominated by fine-grained metal precipitates the 95% confidence interval for predicting mass concentration with an LBSS ranges from ±0.004 mg/l for 0.03 mg/l suspensions to ±0.008 mg/l at 0.12 mg/l. Comparisons among a group of 19 LBSSs found between-instrument variability to reach 70%, but normalizing the raw data using a laboratory calibration procedure reduced the maximum variability to ～8%. |
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