Prochlorococcus & the Secondary Chlorophyll Maximum in the East Tropical North Pacific Oxygen Deficient Zone

Abstract

Oxygen deficient zones are responsible for a major fraction of global ocean nitrogen loss, and these regions are predicted to expand with continued global warming. We investigate a classic feature of these regions, the secondary chlorophyll maximum, that is often dominated by Prochlorococcus. We hypothesize that Prochlorococcus finds a niche at a depth where it can utilize the abundant nitrate that accumulates with depth, beneath competing organisms in the euphotic zone. We find that Prochlorococcus abundance does not correlate with nitrate, and its fluorescence properties in the water column do not seem to match expected growth rates. Prochlorococcus abundance may additionally have a strong advective forcing behind its variability in the water column.