An Ammonium Enrichment Event in the Surface Ocean: Wind Forcing and Potential Ramifications
Nutrient, Ammonium, Nitrate, Nitrite, Oligotrophic, Nanomolar, Sulfur hexafluoride, Wind speed, Barometric pressure, Patch, Weather front, Wind forcing, Exchange, Dispersion, Enrichment
Digital Object Identifier (DOI)
Ammonium is a nutrient frequently preferred by microorganisms that photosynthesize at the base of the marine food web and remove atmospheric carbon dioxide via carbon fixation. Because their photosynthesis is concentrated in the ocean's thin euphotic zone, its nutrient concentrations are critical to oceanic carbon fixation. Identification of replacement processes for euphotic-zone ammonium thus becomes important. These processes were investigated in a two-experiment, Lagrangian field study that produced results consistent with an apparent inverse effect of wind forcing on upper-ocean ammonium concentrations. At low wind speeds (especially ≤ 4 ms− 1), continuous seawater sampling, supported by sulfur-hexafluoride (SF6) water-mass tracing and meteorological measurements, detected 1.1–4.4-km-wide boluses of surface seawater exhibiting ammonium enrichments that were 5 - to-10-fold above background. In the first experiment, ammonium maxima comprising the enrichment event disappeared at higher wind speeds. In the second experiment, which had consistently higher wind speeds, an ammonium event composed of such maxima was never found. The apparent correlation between elevated ammonium concentrations and low wind stress could therefore be viewed as potentially important for understanding ammonium cycling and carbon fixation in the ocean.
Was this content written or created while at USF?
Citation / Publisher Attribution
Marine Chemistry, v. 174, p. 26-34
Scholar Commons Citation
Fanning, Kent A.; Masserini, Robert T. Jr.; Walsh, John J.; Wanninkhof, Rik; Sullivan, K.; Virmani, Jyotika I.; and Heil, Cynthia A., "An Ammonium Enrichment Event in the Surface Ocean: Wind Forcing and Potential Ramifications" (2015). C-IMAGE Publications. 93.