phagotrophy and photolysis

• Main Authors: K. Barbeau, J. W. Moffett
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Pacific; Subarctic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.509.9727; http://www.aslo.org/lo/toc/vol_45/issue_4/0827.pdf

In a previous work, we have employed colloidal ferrihydrite impregnated with an inert radiotracer to probe the mechanistics of iron redox cycling in seawater via phagotrophic and photochemical processes. This paper reports further studies using the inert tracer technique, directed towards obtaining a more quantitative sense of the impor-tance of phagotrophy relative to photolysis as a pathway for the production of bioavailable iron in oxygenated seawater. Our results indicate a maximal (i.e., near-surface at noon) rate of 12 % per day for the photochemically-mediated dissolution of colloidal ferrihydrite. Protozoan-mediated dissolution of the same iron oxide phase proceeds at a rate ranging from 1–6 % per day, depending on grazing turnover rates. Thus, while photolysis should dominate the redox cycling of refractory iron solids in near-surface waters under bright daytime conditions, phagotrophy is likely to be a more important process overall when the entire euphotic zone is considered on a time-averaged basis. Since the first evidence for iron limitation of phytoplank-ton production in high nutrient, low-chlorophyll regions of the world’s oceans (Martin and Fitzwater 1988; Martin and Gordon 1988), the seawater chemistry of iron and its rela-tionship to phytoplankton have been the subject of intense research by a number of groups (for review see Wells et al. 1995; Price and Morel 1998). At this stage, a decade since Martin’s pioneering work in the subarctic North Pacific, there seems little doubt that iron plays a pivotal role in eco-system structure and function in several oceanic regions (e.g.