Biogeochemical origins of particles obtained from the inversion of the volume scattering function and spectral absorption in coastal waters

[摘要] In the aquatic environment, particles can be broadly separated intophytoplankton (PHY), non-algal particle (NAP) and dissolved (or very smallparticle, VSP) fractions. Typically, absorption spectra are inverted toquantify these fractions, but volume scattering functions (VSFs) can also beused. Both absorption spectra and VSFs were used to estimate particlefractions for an experiment in the Chesapeake Bay. A complete set of waterinherent optical properties was measured using a suite of commercialinstruments 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 fewbackward angles measured by a HydroScat-6 and an ECO-VSF agreed with theLISST and MVSM data within 5%, thus indicating inter-instrumentconsistency. The size distribution and scattering parameters for PHY, NAPand VSP were inverted from measured VSFs. For the absorption inversion, the"dissolved" absorption spectra were measured for filtrate passing througha 0.2 μm filter, whereas [Chl] and NAP absorption spectra wereinverted from the particulate fraction. Even though the total scatteringcoefficient showed no correlation with [Chl], estimates of [Chl] from theVSF-inversion agreed well with the HPLC measurements (r = 0.68, meanrelative errors = −20%). The scattering associated with NAP and VSPboth correlated well with the NAP and "dissolved" absorption coefficients,respectively. While NAP dominated forward, and hence total, scattering, ourresults also suggest that the scattering by VSP was far from negligible anddominated 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 estuarineenvironment.

[学科分类] 地球化学与岩石