Inherent Optical Properties (IOPs): Absorption and Beam Attenuation

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	To assist in the interpretation of the data, it can be displayed using the Hawaii Ocean Time-series Data Organization & Graphical System (HOT-DOGS©).

Analytical Method

Profiles of absorption (a(λ)) and beam attenuation (c(λ)) were made using a WET Labs AC-9. The AC-9 simultaneously determined the spectral attenuation and spectral absorption of water at 412, 440, 488, 510, 532, 555, 650, 676 and 715 nm. Each of these wavebands have bandpasses of approximately 10 nm. The sampling frequency is approximately 6 Hz.

The AC-9 was part of an instrument package that also included a Sea-Bird CTD, WET Labs WetStar fluorometer and a Chelsea Fast Repitition Rate Fluorometer (FRRF). The instrument was oriented horizontally and lowered at a more-or-less constant speed of 10 m/min to a bottom depth of approximately 250 m. At least 2 back-to-back profiles were normally taken, one using a 0.2 µm cartridge filter and one without. This allowed the spectral absorption and attenuation coefficient of both the total and dissolved matter to be determined. The particulate absorption and attenuation components were derived by subtracting the dissolved from the total component. The scattering of particles was estimated by subtracting the absorption from the attenuation particle spectrum.

This study is a collaborative effort between the College of Oceanic and Atmospheric Sciences of Oregon State University and the Laboratory for Microbial Oceanography of the University of Hawai'i at Manoa.