The coupled physical‐new production system in the equatorial Pacific during the 1992–1995 El Niño

Stoens, A.; Menkès, Christophe E.; Radenac, Marie-Hélène; Dandonneau, Yves; Grima, Nicolas; Eldin, Gérard; Mémery, Laurent; Navarette, Claudie; André, Jean-Michel; Moutin, Thierry; Raimbault, Patrick

doi:10.1029/98jc02713

Cited by 48 publications

(25 citation statements)

References 72 publications

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“…The general conditions prevailing in the study area are described elsewhere Stoens et al 1999). Briefly, the transect analyzed along 150ЊW ranged from very oligotrophic conditions at 15ЊS with no detectable nutrients in surface to mesotrophic conditions at the equator (Table 1).…”

Section: Resultsmentioning

confidence: 99%

Abundance and diversity of prymnesiophytes in the picoplankton coμmunity from the equatorial Pacific Ocean inferred from 18S rDNA sequences

Staay

Guillou

et al. 2000

Limnology & Oceanography

215

138

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Picoplankton, i.e., cells smaller than 2-3 m, dominate in most open oceanic regions, such as in the Pacific Ocean. In these areas, the dominant carotenoid of photosynthetic eukaryotes is 19Ј-hexanoyloxyfucoxanthin (19HF), considered to be a diagnostic marker for prymnesiophytes. This suggests that this class could be a major component of eukaryotic picoplankton, despite the fact that virtually no prymnesiophyte has been described to date from this size class. To address this question, we assessed prymnesiophyte diversity and abundance in natural picoplankton communities, using a molecular approach. Total genomic DNA was isolated from 3-m-filtered samples collected in the Pacific Ocean. Small subunit (18S) ribosomal RNA genes (rDNA) were amplified by the polymerase chain reaction (PCR) using universal eukaryotic primers. The relative abundance of 18S rDNA from prymnesiophytes was quantified using group-specific and eukaryotic 18S rDNA probes. The percentage of the prymnesiophyte versus total 18S rDNA was much lower than the percentage of prymnesiophytes calculated on the basis of pigment analyses for the same samples. 18S rDNA libraries from five samples were screened using a prymnesiophyte-specific oligonucleotide probe, and 14 nearly complete 18S rDNA sequences were retrieved. Phylogenetic analysis of these sequences established the presence of several prymnesiophyte lineages with no equivalent among cultivated species.It is now well established that cells smaller than 2-3 m (picoplankton), rather than the larger microalgae, dominate the phytoplankton community in the open ocean. In particular, the eukaryotic component of picoplankton, the so-called picoeukaryotes, has been recognized to contribute significantly to both primary biomass and production in open oceanic regions (Campbell et al. 1994;Li 1994). Its taxonomic

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Section: Resultsmentioning

confidence: 99%

Abundance and diversity of prymnesiophytes in the picoplankton coμmunity from the equatorial Pacific Ocean inferred from 18S rDNA sequences

Staay

Guillou

et al. 2000

Limnology & Oceanography

215

138

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“…Early studies using climatological forcing to force basin-wide physical-biological models aimed at characterizing the mean annual nitrate budget in the cold tongue of the Pacific Ocean [Toggweiler and Carson, 1995;Chaiet al, 1996]. Recently, a general circulation model forced with interannually varying winds drove a nitrate transport model [Stoens et al, 1999] that was able to reproduce the main nitrate features observed during JGOFS cruises in 1994. Like in observations, the poor and low new production waters in the western Pacific are concomitant with the fresh warm pool waters.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, we use the same biogeochemical model as Stoens et al [1999] along with satellite and in situ data to better understand how changes in nitrate and new production respond to the variability of physical processes during the exceptionally strong 1997-1998 E1 Nifio and the subsequent La Nifia. In particular, we examine the destruction of the equatorial east-west biogeochemical asymmetry in 1997 and its swift recovery in 1998.…”

Section: Introductionmentioning

confidence: 99%

Modeled and observed impacts of the 1997–1998 El Niño on nitrate and new production in the equatorial Pacific

Radenac¹,

Menkès²,

Vialard³

et al. 2001

J. Geophys. Res.

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Abstract. The impact of the strong 1997-1998 E1Nifio event on nitrate distribution and new production in the equatorial Pacific is investigated, using a combination of satellite and in situ observations, and an ocean circulation-biogeochemical model. The general circulation model is forced with realistic wind stresses deduced from ERS-1 and ERS-2 scatterometers over the 1993-1998 period. Its outputs are used to drive a biogeochemical model where biology is parameterized as a nitrate sink. We first show that the models capture the essential circulation and biogeochemical equatorial features along with their temporal evolution during the 1997-1998 event, although the modeled variability seems underestimated. In particular, the model fails to reproduce unusual bloom conditions. This is attributed to the simplicity of the biological model. An analysis of the physical mechanisms responsible for the dramatic decrease of the biological equatorial production during E1 Nifio is then proposed. During the growth phase (November 1996 through June 1997), nitrate-poor waters of the western Pacific are advected eastward, and the vertical supply of nitrate is reduced due to nitracline deepening. These processes result in the invasion of the equatorial Pacific by nitrate-poor waters during the mature phase (November 1997 through January 1998). At that time, the central Pacific is nitrate limited and experiences warm pool oligotrophic conditions. As a result, the modeled new production over the equatorial Pacific drops by 40% compared to the mean 1993-1996 values. Then, while E1Nifio conditions are still present at the surface, the nitracline shallows over most of the basin in early 1998. Therefore the strengthening of the trade winds in May 1998 efficiently switches on the nitrate vertical supply over a large part of the equatorial Pacific, leading to a rapid return of high biological production conditions. Strong La Nifia conditions then develop, resulting in a biologically rich tongue extending as far west as 160øE for several months.

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“…As such, it characterizes the "biological pump" efficiency. Hence, new production has been widely studied in the equatorial Pacific, using both observation (Dugdale et al, 1992;McCarthy et al, 1996;Turk et al, 2001;Raimbault et al, 1999;Aufdenkampe et al, 2001; and modeling approaches (Laws, 2004;Chavez and Barber, 1987;Radenac et al, 2001;Wang et al, 2006b;Stoens et al, 1998Stoens et al, , 1999Jiang et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Nitrogen uptake and regeneration pathways in the equatorial Pacific: a basin scale modeling study

2009

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Abstract.It is well known that most primary production is fueled by regenerated nitrogen in the open ocean. Therefore, studying the nitrogen cycle by focusing on uptake and regeneration pathways would advance our understanding of nitrogen dynamics in the marine ecosystem. Here, we carry out a basin-scale modeling study, by assessing model simulations of nitrate and ammonium, and rates of nitrate uptake, ammonium uptake and regeneration in the equatorial Pacific. Model-data comparisons show that the model is able to reproduce many observed features of nitrate, ammonium, such as the deep ammonium maximum (DAM). The model also reproduces the observed de-coupling of ammonium uptake and regeneration, i.e., regeneration rate greater than uptake rate in the lower euphotic zone. The de-coupling largely explains the observed DAM in the equatorial Pacific Ocean. Our study indicates that zooplankton excretion and remineralization of organic nitrogen play a different role in nitrogen regeneration. Rates of zooplankton excretion vary from <0.01 mmol m −3 d −1 to 0.1 mmol m −3 d −1 in the upper euphotic zone while rates of remineralization fall within a narrow range (0.015-0.025 mmol m −3 d −1 ). Zooplankton excretion contributes up to 70% of total ammonium regeneration in the euphotic zone, and is largely responsible for the spatial variability of nitrogen regeneration. However, remineralization provides a steady supply of ammonium in the upper ocean, and is a major source of inorganic nitrogen for the oligotrophic regions. Overall, ammonium generation and removal are approximately balanced over the top 150 m in the equatorial Pacific.

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The coupled physical‐new production system in the equatorial Pacific during the 1992–1995 El Niño

Cited by 48 publications

References 72 publications

Abundance and diversity of prymnesiophytes in the picoplankton coμmunity from the equatorial Pacific Ocean inferred from 18S rDNA sequences

Abundance and diversity of prymnesiophytes in the picoplankton coμmunity from the equatorial Pacific Ocean inferred from 18S rDNA sequences

Modeled and observed impacts of the 1997–1998 El Niño on nitrate and new production in the equatorial Pacific

Nitrogen uptake and regeneration pathways in the equatorial Pacific: a basin scale modeling study

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