Characterizations of minerogenic particles in support of modeling light scattering in Lake Superior through a two‐component approach

Abstract

The role of suspended minerogenic particles in light scattering in eastern Lake Superior and Keweenaw Bay (11 sites) during July of 2006 was evaluated with an individual particle analysis technique (scanning electron microscopy interfaced with automated image and X-ray analyses, SAX), along with bulk measurements of particulate scattering and backscattering coefficients (b p and b bp ) and chlorophyll a concentration ([Chl]). SAX measurements provided information on light-scattering attributes of minerogenic particles, including chemical composition and particle size distribution (

Light-absorbing components in Lake Superior

“…1). Site designations (except KW0) are those used by Peng et al (2009). The bay is 36 km long, with widths ranging from 3 to 18 km.…”

“…Partitioning of a into a x contributions for visible wavelengths for multiple sites has not been reported for this lake. Minerogenic particles, mostly clay minerals in the 1-10 μm size range, were found to be an important component of backscattering in eastern Lake Superior and Keweenaw Bay in July of 2006 (Peng et al, 2009). Rigorous partitioning of a according to a x and establishment of relationships between a x and concentrations of optically active constituents have been recommended for the lake to support remote sensing initiatives (Gons and Auer, 2004;Gons et al, 2008).…”

“…Babin and Stramski (2004) reported that absorption by minerogenic particle populations (a m ) was largely attributable to the content of iron (Fe). Recently, advancements have been made in estimating the minerogenic scattering coefficient (b m ) based on an individual particle analysis technique that provides both morphological and chemical characterizations (Scanning electron microscopy interfaced with Automated image and X-ray analyses (SAX)), coupled with forward Mie theory-based calculations Peng et al, , 2009). The integrated SAX-Mie theory approach also represents a basis to directly estimate a m , mediated through the imaginary (absorption) part of the refractive index (Wozniak and Stramski, 2004).…”

“…Symbols and abbreviations adopted in the paper (Table 1) are consistent with those used by the optics research community. Particular attention is given to the role of minerogenic particles and their Fe content in influencing a NAP , based on paired SAX results (Peng et al, 2009) and Mie theory calculations.…”

“…The absorption coefficient, a (m − 1 ), is partitioned according to the additive components (a x ) of colored dissolved organic matter (a CDOM ), non-algal particles (a NAP ), phytoplankton (a ϕ ), and water itself (a w ; known). The role of minerogenic particles and their iron content in regulating a NAP is evaluated based on paired measurements by an individual particle analysis technique (Peng et al, 2009), through empirical analyses and Mie theory calculations of absorption by these particles (a m ). Spectral characteristics of a NAP and a ϕ were consistent with those reported for other case 2 (i.e., phytoplankton not dominant) systems.…”