Red and orange fluorescence and beam attenuation to intermediate depths in the Northeast Pacific Ocea

Continuous profiles to 2000 m of red (chlorophyll) and orange (phycoerythrin) fluorescence and beam attenuation were obtained between 33$spcirc$ and 59$spcirc$N in the Northeast Pacific Ocean. Near-surface maxima in these properties were prominent in the Gulf of Alaska. The strong, shallow orange fluorescence signal suggests that the occurrence of phycoerythrin containing organisms, probably cyanobacteria, is more widespread than previously reported. The underlying chlorophyll fluorescence minimum ($sim$200-300 m) was conspicuous in oligotrophic central gyre waters but limited in eutrophic subarctic waters; the corresponding phycoerythrin fluorescence minimum was prevalent throughout the section. These differences in the fluorescence minima indicate that different processes are involved in the production and degradation of chlorophyll and phycoerythrin containing particles. The tertiary fluorescence maxima ($sim$1000 m) were continuous throughout the Northeast Pacific Ocean. The phycoerythrin fluorescence maximum at depth suggests the presence of heterotrophic cyanobacteria, an hypothesis as yet unsupported by biological evidence.