The 2008 North Atlantic Spring Bloom Experiment: Spectral Particulate Absorption Coefficients

During the 2008 North Atlantic Spring Bloom Experiment (NAB08), spectral absorption coefficients of particulate material were measured by two techniques: the Quantitative Filter Technique (QFT) on water samples collected from the CTD/Rosette and in-water measurements collected with a single ac-9 as the difference between filtered and unfiltered profiles. Phytoplankton and non-phytoplankton absorption spectra from the QFT were determined by the Kishino methanol extraction procedure; these coefficients provide the basis for enhanced separation of ac-9 particulate absorption coefficients into phytoplankton and non- phytoplankton components. The blue-to-red ratio (440nm:676nm) of phytoplankton absorption, a diagnostic of photoprotective pigmentation, varied by approximately 25%. Visible and UV light penetration was measured by two radiometric profiling systems: a free-fall hyperspectral radiometer (350-800nm) deployed from the ship and a hyperspectral radiometer mounted on a Lagrangian mixed-layer float (320-950nm). Despite persistent cloud cover, phytoplankton absorption at wavelengths typically dominated by microsporin-like amino acids (MAAs, ~ 320nm) were observed in all spectra in the upper 50m. Phytoplankton community composition changed over the course of the experiment, from a diatom-dominated assemblage to a mixed community of dinoflagellates, picoeukaryotes, and heterotrophic flagellates.