Nitrogen regeneration in the NE Atlantic Ocean and its impact on seasonal new, regenerated and export production

Fernández, I Camila; Raimbault, Patrick

doi:10.3354/meps337079

Cited by 30 publications

(33 citation statements)

References 37 publications

(78 reference statements)

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“…This result confirms the significant role of nitrification in the upper layers of oceanic waters, as previously reported in the equatorial Pacific, where 20 to 100% of the total nitrate demand was fueled by nitrification (Raimbault et al, 1999) and 142% at station ALOHA (Dore and Karl, 1996). The role of nitrification in providing regenerated nitrate in the euphotic zone has been confirmed by recent findings in the Atlantic, as well as in the Mediterranean Sea, where nitrification can support 25 to 100% of the new production (Diaz and Raimbault, 2000;Fernandez and Raimbault, 2007). A logical conclusion is that there could be overestimations in new production data when all the nitrogen regeneration processes are not taken into account.…”

Section: Discussionsupporting

confidence: 76%

“…Nitrification rates presented here (Table 2) are in the range of previous observations (e.g. Ward and Zafiriou, 1988;Bianchi et al, 1994;Raimbault et al, 1999;Fernandez and Raimbault, 2007). Regeneration processes were active throughout the water column, even in the oligotrophic waters of the SPG and were largely able to sustain the phytoplanktonic demand in the photic layer (Table 2).…”

Section: Discussionsupporting

confidence: 74%

“…the <0.7 µm size fraction, following 24-h incubations (Table 1). The low efficiency of the GF/F filters for PON retention compared to 0.2-µm membranes is now well-documented in a variety of marine environments (Altabet, 1990;Libby and Wheeler, 1997;Slawyk and Raimbault, 1995;Raimbault et al, 2000;Fernandez et al, 2007) and has been confirmed during this study . Our experiments showed that the use of GF/F filters can result in severe underestimations of ammonium uptake during high productivity, as well as under oligotrophic conditions.…”

Section: Discussionsupporting

confidence: 52%

“…Rates of NH 4 regeneration are rare for oceanic waters but our results are in the range of the data available (e.g. Bode et al, 2002;Raimbault et al, 1999;Fernandez and Raimbault, 2007). Ammonium regeneration showed high rates (up to 500 nmoles l −1 d −1 ) in the high productive Marquesas and upwelling regions (MAR and UPW), but significant activity was also measured in the SPG (10-20 nmoles l −1 d −1 ); these rates were able to sustain the biological demand.…”

Section: Discussionmentioning

confidence: 71%

“…between the low loss rates (<15%) found in the equatorial Pacific (Raimbault et al, 1999 and the very high ones (74%) found in the Southern California Bight by Bronk and Glibert (1991). They are also in the same order of magnitude as those found in the Mediterranean Sea during spring (Diaz and Raimbault, 2000) and in the Atlantic Ocean (Fernandez and Raimbault, 2007). However, one should keep in mind that ρ loss does not represent the total flux of nitrogen from the particulate organic matter (PON) in the DON pool .…”

Section: Discussionmentioning

confidence: 88%

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Evidence for efficient regenerated production and dinitrogen fixation in nitrogen-deficient waters of the South Pacific Ocean: impact on new and export production estimates

2008

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Abstract.One of the major objectives of the BIOSOPE cruise, carried out on the R/V Atalante from OctoberNovember 2004 in the South Pacific Ocean, was to establish productivity rates along a zonal section traversing the oligotrophic South Pacific Gyre (SPG). These results were then compared to measurements obtained from the nutrient -replete waters in the Chilean upwelling and around the Marquesas Islands. A dual 13 C/ 15 N isotope technique was used to estimate the carbon fixation rates, inorganic nitrogen uptake (including dinitrogen fixation), ammonium (NH 4 ) and nitrate (NO 3 ) regeneration and release of dissolved organic nitrogen (DON). The SPG exhibited the lowest primary production rates (0.15 g C m −2 d −1 ), while rates were 7 to 20 times higher around the Marquesas Islands and in the Chilean upwelling, respectively. In the very low productive area of the SPG, most of the primary production was sustained by active regeneration processes that fuelled up to 95% of the biological nitrogen demand. Nitrification was active in the surface layer and often balanced the biological demand for nitrate, especially in the SPG. The percentage of nitrogen released as DON represented a large proportion of the inorganic nitrogen uptake (13-15% in average), reaching 26-41% in the SPG, where DON production played a major role in nitrogen cycling. Dinitrogen fixation was detectable over the whole study area; even in the Chilean upwelling, where rates as high as 3 nmoles l −1 d −1 were measured. In these nutrient-replete waters new production was very high (0.69±0.49 g C m −2 d −1 ) and essentially sustained by nitrate levels. In the SPG, dinitrogen fixation, although occurring at much lower daily rates (≈1-2 nmoles l −1 d −1 ), sustained up to 100% of the new production (0.008±0.007 g C m −2 d −1 ) which was two orders of magnitude lower than that measured in the upwelling. The annual N 2 -fixation of the South PacificCorrespondence to: P. Raimbault (patrick.raimbault@univmed.fr) is estimated to 21×10 12 g, of which 1.34×10 12 g is for the SPG only. Even if our "snapshot" estimates of N 2 -fixation rates were lower than that expected from a recent ocean circulation model, these data confirm that the N-deficiency South Pacific Ocean would provide an ideal ecological niche for the proliferation of N 2 -fixers which are not yet identified.

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