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

By P. Raimbault, N. Garcia. 2008

132 citations recorded by the source corpus.

Abstract. One of the major objectives of the BIOSOPE cruise, carried out on the R/V Atalante from October-November 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 13C/15N isotope technique was used to estimate the carbon fixation rates, inorganic nitrogen uptake (including dinitrogen fixation), ammonium (NH4) and nitrate (NO3) 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 N2-fixation of the South Pacific is estimated to 21×1012g, of which 1.34×1012g is for the SPG only. Even if our "snapshot" estimates of N2-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 N2-fixers which are not yet identified.

Subfields: Ecology, Oceanography

View Paper: https://www.semanticscholar.org/paper/7cc282d45a6a11a0cbeaff4df8a11ab1c395f1b5

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Citations in the corpus

Diversity and activity of nitrogen‐fixing communities across ocean basins (2017, background): “In the ESP, the relatively low NFR we report for the gyre (< 1 nmol N L21 d21) also agree with previous studies (Raimbault and Garcia 2008; Halm et al. 2011).”
Evidence of active dinitrogen fixation in surface waters of the eastern tropical South Pacific during El Niño and La Niña events and evaluation of its potential nutrient controls (2013, background): “The paucity of observations and the few direct measurements of N2 fixation rates in this region [Raimbault and Garcia, 2008; Moutin et al., 2008; Fernandez et al., 2011] make it difficult to draw conclusions concerning the biogeochemical importance of diazotrophy in the ETSP, which motivated this…”
Alkaline phosphatase activity in the subtropical ocean: insights from nutrient, dust and trace metal addition experiments (2014, background): “…in the subtropical North Atlantic (250 µmol N m−2 d−1; Capone et al., 2005) relative to the North Pacific (30–120 µmol N m−2 d−1; Dore et al., 2002) and South Pacific (30–70 µmol N m−2 d−1; Raimbault and Garcia, 2008), where nitrogen fixation is considered to be iron limited (Sohm et al., 2011).”