Diel variability of the beam attenuation and backscattering coefficients in the northwestern Mediterranean Sea (BOUSSOLE site)

Type Article
Date 2014-08
Language English
Author(s) Kheireddine Malika1, 2, Antoine David1, 2, 3
Affiliation(s) 1 : Univ Paris 06, Univ Paris 04, Lab Oceanog Villefranche, Observ Oceanol,UMR 7093, Villefranche Sur Mer, France.
2 : CNRS, Observ Oceanol, Lab Oceanog Villefranche, UMR 7093, Villefranche Sur Mer, France.
3 : Curtin Univ, Dept Imaging & Appl Phys, Remote Sensing & Satellite Res Grp, Perth, WA 6845, Australia.
Source Journal Of Geophysical Research-oceans (0148-0027) (Amer Geophysical Union), 2014-08 , Vol. 119 , N. 8 , P. 5465-5482
DOI 10.1002/2014JC010007
WOS© Times Cited 28
Abstract The diel variability of the particulate beam attenuation coefficient, cp, and of the particulate backscattering coefficient, bbp, were investigated during five seasonal cycles at an oceanic site in the northwestern Mediterranean Sea, covering contrasting physical and trophic situations. We observed a diel cycle in cp and bbp, related to changes in phytoplankton properties (i. e., size and refractive index) induced by the accumulation of carbon within phytoplankton cells associated with photosynthetic processes, during the winter mixing of the water column, the development of the spring phytoplankton bloom, its decline, and during the summer oligotrophy. The relative amplitude of the cp diel variability was much larger during the spring bloom (20-50%) than during other seasons (10-20%), whereas that of bbp is steadily around 20% and does not show significant seasonal variability. The minimal cp and bbp occurred at sunrise and are synchronized, whereas maximum bbp values are often reached 3-6 h before those for cp (except during bloom conditions), which occur near sunset. These different amplitudes and timing are tentatively explained using Mie computations, which allow discerning the respective roles of changes in the particle size distribution and refractive index. The differences observed here in the diel cycles of cp and bbp show that they cannot be used interchangeably to determine the daily increase of the particle pool. This result has implications on the feasibility to determine net community production from the bbp diel changes, when only bbp is measured in situ or available from ocean color observations.
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