Garcia-Robledo E., Padilla C. C., Aldunate M., Stewart F. J., Ulloa O., Paulmier Aurélien, Gregori G., Revsbech N. P. (2017). Cryptic oxygen cycling in anoxic marine zones. Proceedings of the National Academy of Sciences of the United States of America, 114 (31), p. 8319-8324. ISSN 0027-8424.
Garcia-Robledo E., Padilla C. C., Aldunate M., Stewart F. J., Ulloa O., Paulmier Aurélien, Gregori G., Revsbech N. P.
Source
Proceedings of the National Academy of Sciences of the United States of America, 2017,
114 (31), p. 8319-8324 ISSN 0027-8424
Oxygen availability drives changes in microbial diversity and biogeochemical cycling between the aerobic surface layer and the anaerobic core in nitrite-rich anoxic marine zones (AMZs), which constitute huge oxygen-depleted regions in the tropical oceans. The current paradigm is that primary production and nitrification within the oxic surface layer fuel anaerobic processes in the anoxic core of AMZs, where 30-50% of global marine nitrogen loss takes place. Here we demonstrate that oxygenic photosynthesis in the secondary chlorophyll maximum (SCM) releases significant amounts of O-2 to the otherwise anoxic environment. The SCM, commonly found within AMZs, was dominated by the picocyanobacteria Prochlorococcus spp. Free O-2 levels in this layer were, however, undetectable by conventional techniques, reflecting a tight coupling between O-2 production and consumption by aerobic processes under apparent anoxic conditions. Transcriptomic analysis of the microbial community in the seemingly anoxic SCM revealed the enhanced expression of genes for aerobic processes, such as nitrite oxidation. The rates of gross O-2 production and carbon fixation in the SCM were found to be similar to those reported for nitrite oxidation, as well as for anaerobic dissimilatory nitrate reduction and sulfate reduction, suggesting a significant effect of local oxygenic photosynthesis on Pacific AMZ biogeochemical cycling.
