Mechanisms of P* Reduction in the Eastern Tropical South Pacific

摘要: Water masses influenced by oxygen minimum zones (OMZ) feature low inorganic nitrogen (N) to phosphorus (P) ratios. The surplus of P over N is thought favor non-Redfield primary production bloom-forming phytoplankton species. Additionally, excess phosphate (P*) provide a niche for fixing organisms. In order assess the effect nutrient ratios on stoichiometry and composition producers, biogeochemical measurements were carried out in 2012 during research cruise eastern tropical South Pacific (ETSP). Based pigment analyses, succession different functional groups was observed along onshore – offshore transects with diatoms dominating productive upwelling region, prymnesiophytes, cryptophytes Synechococcus prevailing oligotrophic open ocean. Although supply below Redfield proportions throughout sampling area, particulate organic (PON:POP) generally exceeded 16:1. Despite PON:POP ≥ 16, high P* values surface layer (0-50 m) above shelf rapidly decreased as water advected offshore. There are three mechanisms which can explain these observations: (1) production, where biomass directly released dissolved (DOP), (2) masked matter pool mainly consisting P-depleted detrital biomass, and/or (3) combined dinitrogen (N2) fixation. Our observations suggest that processes occur simultaneously study area; quantifying relative importance each needs further investigation. Therefore, it remains uncertain whether ETSP net sink bioavailable or N-deficit this area replenished locally.