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Title: Microbial uptake and regeneration of inorganic nitrogen off the coastal Namibian upwelling system
Authors: Benavides Gorostegui,Mar 
Santana Falcon, Yeray 
Wasmund, Norbert
Aristegui, Javier 
UNESCO Clasification: 251001 Oceanografía biológica
Keywords: Eastern boundary currents
Primary production
Dissolved organic nitrogen
Ammonium regeneration
Issue Date: 2014
Publisher: 0924-7963
Project: Intercambio Plataforma-Oceano en El Ecosistema Marino de Las Islas Canarias-Peninsula Iberica (Caibex):Afloramiento de Cabo Guir 
Zonas de Mezcla y Frentes en El Océano Oscuro Como ¿Hot-Spots? de Biodiversidad y Flujos Biogeoquímicos A Través Del Mar Mediterráneo y Atlántico Nordeste - I. 
Journal: Journal of Marine Systems 
Abstract: We used 15N-labeled substrates to measure microbial nitrate (NO3−) and ammonium (NH4+) uptake, regeneration and associated dissolved organic nitrogen (DON) release in a coastal upwelling system off Namibia (Benguela Current) in the austral winter of 2011 with the aim of quantifying rates of new production (Pnew) and regenerated production (Preg). These measurements were made during four consecutive coastal-offshore transects. The water parcels sampled at the different stations over the transect were classified into three groups according to the time passed from the first contact of the water with the surface during coastal upwelling (‘pseudo-age’). The average Pnew was high in freshly upwelled waters with a pseudo-age < 13 d (17.8 mmol N m− 2 h− 1), and decreased abruptly towards older waters (3.9 and 2.3 mmol N m− 2 h− 1 in waters with a pseudo-age of 13 to 55 d, and > 55 d, respectively). Preg rates were similar in < 13 d and 13–55 d waters (10.9 and 11.1 mmol N m− 2 h− 1, respectively), and decreased to 6.24 mmol N m− 2 h− 1 in waters with a pseudo-age > 55 d. Measuring nitrogen regeneration and DON release fluxes allowed us to correct Pnew and Preg rates. NO3− regeneration rates were low (< 0.5 mmol N m− 2 h− 1), while NH4+ regeneration rates were in the range of NH4+ uptake rates (~ 2 to 5 mmol N m− 2 h− 1), thus influencing significantly Preg rates. Parallel studies presented in this volume indicate a relatively high abundance of dinoflagellates and mixotrophic microflagellates, which may be partly responsible for the high Preg rates observed. Our results suggest that nitrogen regeneration plays an important role in sustaining primary production in this upwelling system.
ISSN: 0924-7963
DOI: 10.1016/j.jmarsys.2014.05.002
Source: Journal Of Marine Systems [ISSN 0924-7963], v. 140, p. 123-129
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