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In situ variability of mass‐specific beam attenuation and backscattering of marine particles with respect to particle size, density, and composition
Author(s) -
Neukermans Griet,
Loisel Hubert,
Mériaux Xavier,
Astoreca Rosa,
McKee David
Publication year - 2012
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2012.57.1.0124
Subject(s) - attenuation , particle size , particulates , particle (ecology) , analytical chemistry (journal) , mass fraction , attenuation coefficient , particle size distribution , range (aeronautics) , chemistry , particle density , seawater , particle number , mineralogy , volume (thermodynamics) , materials science , optics , physics , environmental chemistry , geology , oceanography , thermodynamics , organic chemistry , composite material
This study analyzes relationships between concentration of suspended particles represented by dry mass, [SPM], or area, [AC], and optical properties including particulate beam attenuation ( c p ), side scattering ( b s ), and backscattering ( b bp ), obtained from an intensive sampling program in coastal and offshore waters around Europe and French Guyana. First‐order optical properties are driven by particle concentration with best predictions of [SPM] by b bp and b s , and of [AC] by c p . Second‐order variability is investigated with respect to particle size, apparent density (dry weight‐to‐wet‐volume ratio), and composition. Overall, the mass‐specific particulate backscattering coefficient, b m bp ( = b bp : [SPM]), is relatively well constrained, with variability of a factor of 3–4. This coefficient is well correlated with particle composition, with inorganic particles having values about three times greater ( b m bp = 0.012 m 2 g −1 ) than organic particles ( b m bp = 0.005 m 2 g −1 ). The mass‐specific particulate attenuation coefficient, c m p ( = c p : [SPM]), on the other hand, varies over one order of magnitude and is strongly driven (77% of the variability explained) by particle apparent density. In this data set particle size does not affect c m p and affects b m bp only weakly in clear (case 1) waters, despite size variations over one order of magnitude. A significant fraction (40–60%) of the variability in b m bp remains unexplained. Possible causes are the limitation of the measured size distributions to the 2–302‐µm range and effects of particle shape and internal structure that affect b bp more than c p and were not accounted for.