Spectral absorption properties of mineral particles in western Lake Erie: Insights from individual particle analysis

Abstract

The light-absorbing attributes of minerogenic particle populations were determined for clay-mineral-enriched conditions at 14 sites in the western basin of Lake Erie following a wind-driven re-suspension event. Estimates of spectral absorption properties of the minerogenic particle assemblages, namely the imaginary part of the refractive index (n9), the mean absorption efficiency factor (,Q a,m .), the mean package effect index (,Q à a,m .), and the mass-specific absorption coefficient (a à m ), are presented. These were based on laboratory measurements of non-algal particulate absorption (a NAP ), minerogenic particle size distributions (PSD) with an individual particle analysis technique, and iterative Mie theory calculations to retrieve n9(l). There were wide spatial differences in magnitudes of these estimates. The n9(l) values are generally consistent with those obtained with a different methodology. Absorption by minerogenic particles was dominated by clay mineral particles in the 2-20 mm size range. The effects of n9 and PSD variations on both ,Q a,m . and ,Q à a,m . were well-parameterized in the multiplicative format of optical thickness, and were qualitatively consistent with the literature and Mie theoretical predictions for monodispersed spheres. Spatial differences in n9 and PSD were both important drivers of the variations in ,Q a,m . and ,Q à a,m .. Mie theory calculations indicate that absorption by these minerogenic particles causes substantial decreases in their spectral scattering, backscattering, and backscattering ratio, from the red to the blue spectral regions, relative to the case of non-absorbing.

Advancing two‐component partitioning of light scattering in C ayuga L ake, N ew Y ork

“…c,e,f), can be converted to approximations based on mass‐specific coefficients with some additional insights provided by SAX. Volume concentrations of minerogenic particles (PVV m , as written analogously to PAV m ) can be estimated from SAX results (Peng and Effler ), and we observed the average PAV m : PVV m ratio for this study to be 0.54 m −1 mm −3 L. With a reasonable density value of dry clay mineral (e.g., 2.6 × 10 6 g m −3 ; Babin et al ; Peng and Effler ), the PIM‐normalized b m and b b,m (at 660 nm) are estimated to be 0.49 m 2 g −1 and 0.013 m 2 g −1 , respectively. Assuming a POC : POM ratio of ∼ 0.4 (Redfield et al ; Monteiro et al ), the POM‐normalized b o and b b,o are estimated to be 0.94 m 2 g −1 and 0.0051 m 2 g −1 , respectively.…”

“…The n (real part, considered spectrally flat) values were consistent with earlier SAX–Mie applications (e.g., Peng et al , 2009 a ), including the long‐term study of Cayuga Lake minerogenic particle optics (Effler and Peng ). The adopted values of n ′ were lower than those used in earlier studies (e.g., 10 −4 instead of 10 −3 at 660 nm for clay minerals), based on new absorption information (Peng and Effler ). The average scattering and backscattering efficiencies of minerogenic particles were calculated as …”

“…In addition, 532 nm is frequently used as the reference when spectral optical variability and backscattering ratios are reported (e.g., Snyder et al ; McKee et al ; Sun et al ). Values of the refractive indices ( m = n − in ′, where n and n ′ are the real and imaginary parts relative to water; Table ) were specified on the basis of particle type classification and literature listings (e.g., Babin et al ; Woźniak and Stramski ) and a recent study of the spectral absorbing properties of mineral particles in Lake Erie (Peng and Effler ). The n (real part, considered spectrally flat) values were consistent with earlier SAX–Mie applications (e.g., Peng et al , 2009 a ), including the long‐term study of Cayuga Lake minerogenic particle optics (Effler and Peng ).…”

“…Values selected on the basis ofBabin et al (2003) and Wo zniak and, spectrally uniform. † Study averages fromPeng and Effler (2013).…”

Characterizations of calcite particles and evaluations of their light scattering effects in lacustrine systems

“…The calculated Q values depend on λ , particle size ( d i ) and composition, the latter represented by the relative (to water) complex refractive index ( m = n – in ′, where n and n ′ are the real and imaginary parts). Values of n and n ′ were specified (Table ) according to the composition of particles (e.g., Peng et al ), as guided by literature listings for minerals (Kerr and Rogers ; Woźniak and Stramski ) and the results of a recent analysis for n ′ (Peng and Effler ). There is distinct uncertainty or variability in n for calcite according to literature source (e.g., Table ).…”