ASLO/TOS Ocean Research Conference, Honolulu, HI, February 2004, p. 92.

Assessing phytoplankton biomass and physiological variability at Station ALOHA (22 45'N, 158 00'W) using radiance reflectance profiles

R. M. Letelier¹, M. R. Abbott¹, D. M. Karl², J. Nahorniak¹, R. R. Bidigare², G. Corno¹

¹Oregon State University, Corvallis, USA

²University of Hawaii, Honolulu, USA

Nearly monthly deployments of a Profiling Reflectance Radiometer (PRR) have been made at Station ALOHA (22 45 N, 158 W) as part of the Hawaii Ocean Time-series program since February 1998. Profiles of chlorophyll a (chl a) concentration and yellow substance absorption at 440 nm have been derived from downwelling irradiance measurements at three wavebands. In addition upwelling radiance at 683 nm measured by the PRR allows the quantification of chl a passive fluorescence. Based on these measurements we derive vertical profiles of fluorescence quantum yield for the phytoplankton assemblage and analyze the seasonal and interannual variability in the context of other HOT core measurements. Furthermore we compare this variability with that derived from primary production estimated by ¹⁴C in situ uptake and Fast Repetition Rate fluorometry (FRRf). Preliminary results suggest that fluorescence quantum yield in the study area does not vary significantly over time with the exception of periods when summer phytoplankton blooms are observed. We will discuss possible causes of the apparent uncoupling between the observed variability in the fuorescence quantum yield, ¹⁴C derived Primary Production and FRRf derived photosynthetic parameters.