Publication Date:
2024-03-13
Description:
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°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 N2 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 N2 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.
Keywords:
Ammonium; Clarke-type sensor; Colorimetric; CTD; Date/Time of event; DEPTH, water; Elevation of event; Event label; Fluorescence; GENUS; Geochemistry and ecology of the Namibian upwelling system; Helmholtz-Zentrum Geesthacht, Institute of Coastal Research; HZG; Isotope ratio mass spectrometry; Latitude of event; Longitude of event; M76/2; M76/2_192_WS; M76/2_194_WS; M76/2_195_WS; M76/2_196_WS; M76/2_198_WS; M76/2_200_WS; M76/2_201_WS; M76/2_202_WS; M76/2_204_WS; M76/2_206_WS; M76/2_207_WS; M76/2_214_WS; M76/2_215_WS; M76/2_216_WS; M76/2_218_WS; M76/2_220_WS; M76/2_225_WS; M76/2_230_WS; M76/2_231_WS; M76/2_243_WS; M76/2_252_WS; Meteor (1986); Namibia upwelling, Southeast Atlantic; Nitrate; Nitrite; Oxygen; Phosphate; Salinity; Silicate; Temperature, water; Water sample; WS; δ15N, nitrate
Type:
Dataset
Format:
text/tab-separated-values, 1468 data points
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