BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-10-6029-2013 Biogeochemical origins of particles obtained from the inversion of the volume scattering function and spectral absorption in coastal waters Zhang X. https://orcid.org/0000-0002-2982-210X 1 Huot Y. 2 Gray D. J. 3 Weidemann A. 4 Rhea W. J. 3 Earth System Science and Policy, University of North Dakota, Grand Forks, North Dakota 58202, USA Centre d'applications et de recherches en télédétection, Université de Sherbrooke, Sherbrooke, QC J1K 2R1, Canada US Naval Research Laboratory Code 7231, Washington, DC 20375, USA US Naval Research Laboratory Code 7330, Stennis Space Center, MS 39529, USA 13 09 2013 10 9 6029 6043 Copyright: © 2013 X. Zhang et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/10/6029/2013/bg-10-6029-2013.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/10/6029/2013/bg-10-6029-2013.pdf

In the aquatic environment, particles can be broadly separated into phytoplankton (PHY), non-algal particle (NAP) and dissolved (or very small particle, VSP) fractions. Typically, absorption spectra are inverted to quantify these fractions, but volume scattering functions (VSFs) can also be used. Both absorption spectra and VSFs were used to estimate particle fractions for an experiment in the Chesapeake Bay. A complete set of water inherent optical properties was measured using a suite of commercial instruments and a prototype Multispectral Volume Scattering Meter (MVSM); the chlorophyll concentration, [Chl] was determined using the HPLC method. The total scattering coefficient measured by an ac-s and the VSF at a few backward angles measured by a HydroScat-6 and an ECO-VSF agreed with the LISST and MVSM data within 5%, thus indicating inter-instrument consistency. The size distribution and scattering parameters for PHY, NAP and VSP were inverted from measured VSFs. For the absorption inversion, the "dissolved" absorption spectra were measured for filtrate passing through a 0.2 μm filter, whereas [Chl] and NAP absorption spectra were inverted from the particulate fraction. Even though the total scattering coefficient showed no correlation with [Chl], estimates of [Chl] from the VSF-inversion agreed well with the HPLC measurements (<i>r</i> = 0.68, mean relative errors = −20%). The scattering associated with NAP and VSP both correlated well with the NAP and "dissolved" absorption coefficients, respectively. While NAP dominated forward, and hence total, scattering, our results also suggest that the scattering by VSP was far from negligible and dominated backscattering. Since the sizes of VSP range from 0.02 to 0.2 μm, covering (a portion of) the operationally defined "dissolved" matter, the typical assumption that colored dissolved organic matter (i.e., CDOM) does not scatter may not hold, particularly in a coastal or estuarine environment.

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