Hilfe Wegweiser Datenschutzhinweis Impressum Kontakt





N-cycling and balancing of the N-deficit generated in the oxygen minimum zone over the Namibian shelf-An isotope-based approach

Es sind keine MPG-Autoren in der Publikation vorhanden
Externe Ressourcen
Es sind keine Externen Ressourcen verfügbar
Volltexte (frei zugänglich)
Es sind keine frei zugänglichen Volltexte verfügbar
Ergänzendes Material (frei zugänglich)
Es sind keine frei zugänglichen Ergänzenden Materialien verfügbar

Nagel, B., Emeis, K.-C., Flohr, A., Rixen, T., Schlarbaum, T., Mohrholz, V., et al. (2013). N-cycling and balancing of the N-deficit generated in the oxygen minimum zone over the Namibian shelf-An isotope-based approach. Journal of Geophysical Research-Biogeosciences, 118(1), 361-371. doi:10.1002/jgrg.20040.

The northern Benguela upwelling system is a nutrient-replete region with high plankton biomass production and a seasonally changing oxygen minimum zone. Nitrate: phosphate ratios in fresh upwelling water are low due to denitrification in the near-seafloor oxygen minimum zone and phosphate efflux from sediments. This makes the region a candidate for substantial dinitrogen fixation, for which evidence is scarce. Nutrient and oxygen data, N isotope data of nitrate, nitrogen isotope ratios of particulate matter, particulate organic carbon content, and suspended matter concentrations on a transect across the shelf and upper slope at 23 degrees S illustrate N-cycling processes and are the basis for estimating the contribution of N-sources and N-sinks to the reactive nitrogen pool. It appears that N-removal due to denitrification exceeds N gain by N-2 fixation and physical mixing processes by a factor of >6, although inorganic N: P ratios again increase as surface water is advected offshore. Nitrate and ammonium regeneration, nutrient assimilation with N:P < 16, shelf break mixing, atmospheric input, and N-2 fixation all contribute to the restoration of inorganic N: P ratios back to Redfield conditions, but in seasonally changing proportions. The Benguela upwelling system thus is a nutrient source for the oceanic-mixed layer where N-sources and N-sinks are not in balance and Redfield conditions can only re-adjust by advection and mixing processes integrated over time.