In situ variability of mass‐specific beam attenuation and backscattering of marine particles with respect to particle size, density, and composition

Abstract

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 bp remains unexplained. Possible causes are the limitation of the measured size distributions to the 2-302-mm range and effects of particle shape and internal structure that affect b bp more than c p and were not accounted for.

Optical techniques for remote and in-situ characterization of particles pertinent to GEOTRACES

“…The variability in mass specific optical properties, when compared across studies, has been found to be constrained within ±50% despite some variability in the analytical methods used to obtain mass (Boss et al, 2009c;Cetinic et al, 2012;Hill et al, 2011;Neukermans et al, 2012) and large variability in the environments sampled. Note that in all these studies measurements have been done using red or near-infra-red wavelengths (650 nm < k < 880 nm) to minimize the effect of dissolved substance absorption on the attenuation coefficient, as well as to minimize the effect of particulate absorption on the scattering coefficient.…”

“…Remote sensing requirements and the need to understand coastal and near bottom processes, stimulated the development of PM/POC -backscattering proxies (Boss et al, 2009c;Cetinic et al, 2012;Neukermans et al, 2012;Stramski et al, 1999). The availability of relatively cheap and large-depth capable side-scattering (turbidity) sensors encouraged studies relating side-scattering and POC or PM (Baker et al, 2001;Bishop and Wood, 2008;Boss et al, 2009c;Bishop et al, 2012;Cetinic et al, 2012).…”

“…The introduction of the first commercial transmissometers spawned the investigation of PM and particulate organic carbon concentration (POC) relationships with beam attenuation coefficient (Bishop, 1986(Bishop, , 1999Bishop et al, 1999Bishop et al, , 1992Bishop and Joyce, 1986;Bishop and Wood, 2008;Cetinic et al, 2012;Gardner, 1989a;Gardner et al, 1985Gardner et al, , 2003Gardner et al, , 1993Hill et al, 2011;Karageorgis et al, 2008Karageorgis et al, , 2014Neukermans et al, 2012). The beam attenuation coefficient was found to be a better proxy for POC than for PM for waters dominated by biogenic particles, having a smaller intercept and a significantly higher correlation coefficient (Bishop, 1999;Gardner et al, 2003).…”

“…Nonetheless several studies have used them in the upper ocean with success (Neukermans et al, 2012;Reynolds et al, 2010).…”

Potential of High Spatial and Temporal Ocean Color Satellite Data to Study the Dynamics of Suspended Particles in a Micro-Tidal River Plume

“…This Wetlabs ECO-BB2FL sensor measures light backscattering at 117˝at the fixed wavelength of 700 nm (β 117 (700) in sr´1¨m´1) as well as chlorophyll fluorescence at a sample rate of 15 minutes (Figure 2). The measured β 117 (700) data (in sr´1¨m´1) was converted into the particulate backscattering coefficient (b bp (700), in m´1) which is a robust proxy of the SPM concentration [8, 29,31]. The b bp (700) coefficient was obtained through the formula b bp (700) = 2πˆ1.1ˆβ p117 (700) [29], with β p117 (700) = β 117 (700) -β w117 (700)~β 117 (700), as the water light backscaterring (β w117 (700)~10´5) is negligible compared to particulate light backscattering signal (β p117 (700)~10´2) in turbid waters.…”