Estimates of vertical eddy diffusion through the thermocline from phytoplankton nitrate uptake rates in the mixed layer of the eastern tropical Pacific1

King, Frederick D.; Devol, Allan H.

doi:10.4319/lo.1979.24.4.0645

Cited by 88 publications

(28 citation statements)

References 13 publications

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“…Using integrated nitrate uptake rates measured in the SPG (60 µmoles m −2 d −1 ; Raimbault and Garcia, 2007) and nitrate gradients from the top of the thermocline (75.4±22 µmoles m −4 ), the Kz value is estimated (0.76±0.81 m 2 d −1 =0.09±0.1 cm 2 s −1 ). This value agrees with previous results obtained from oceanic waters (Eppely et al, 1979;King and Devol;Lewis et al, 1986) ranging from 0.06 to 0.75 cm 2 s −1 . The diffusive fluxes of inorganic and organic dissolved nutrients in the SPG calculated using this Kz value, are presented in Table 3.…”

Section: Discussionsupporting

confidence: 83%

“…Values for ε as well as for Kz are rarely experimentally available, especially in oceanic waters. However, assuming the only nitrate source for phytoplankton growth comes from deep water via turbulent diffusion, we can propose that the biological nitrate uptake is equal to this diffusive flux, as suggested by King and Devol (1979). Using integrated nitrate uptake rates measured in the SPG (60 µmoles m −2 d −1 ; Raimbault and Garcia, 2007) and nitrate gradients from the top of the thermocline (75.4±22 µmoles m −4 ), the Kz value is estimated (0.76±0.81 m 2 d −1 =0.09±0.1 cm 2 s −1 ).…”

Section: Discussionmentioning

confidence: 99%

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Distribution of inorganic and organic nutrients in the South Pacific Ocean − evidence for long-term accumulation of organic matter in nitrogen-depleted waters

2008

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Abstract. During the BIOSOPE cruise the RV Atalante was dedicated to study the biogeochemical properties in the South Pacific between the Marquesas Islands (141 • W-8 • S) and the Chilean upwelling (73 • W-34 • S). Over the 8000 km covered by the cruise, several different trophic situations were encountered, in particular strong oligotrophic conditions in the South Pacific Gyre (SPG, between 123 • W and 101 • W). In this isolated region, nitrate was undetectable between the surface and 160-180 m and only trace quantities (<20 nmoles l −1 ) of regenerated nitrogen (nitrite and ammonium) were detected, even in the subsurface maximum. Integrated nitrate over the photic layer, which reached 165 m, was close to zero. Despite this severe nitrogendepletion, phosphate was always present in significant concentrations (≈0.1 µmoles l −1 ), while silicic acid was maintained at low but classical oceanic levels (≈1 µmoles l −1 ). In contrast, the Marquesas region (MAR) to the west and Chilean upwelling (UPW) to the east were characterized by high nutrient concentrations, one hundred to one thousand fold higher than in the SPG. The distribution of surface chlorophyll reflected the nitrate gradient, the lowest concentrations (0.023 nmoles l −1 ) being measured at the centre of the SPG, where integrated value throughout the photic layer was very low (≈ 10 mg m −2 ). However, due to the relatively high concentrations of chlorophyll-a encountered in the DCM (0.2 µg l −1 ), chlorophyll-a concentrations throughout the photic layer were less variable than nitrate concentrations (by a factor 2 to 5). In contrast to chlorophyll-a, integrated particulate organic matter (POM) remained more or less constant along the study area (500 mmoles m −2 , 60 mmoles m −2 and 3.5 mmoles m −2 for particulate organic carbon, particulate organic nitrogen and particulate organic phosphorus, Correspondence to: P. Raimbault (patrick.raimbault@univmed.fr) respectively), with the exception of the upwelling, where values were two fold higher. The residence time of particulate carbon in the surface water was only 4-5 days in the upwelling, but up to 30 days in the SPG, where light isotopic δ 15 N signal noted in the suspended POM suggests that N 2 -fixation provides a dominant supply of nitrogen to phytoplankton. The most striking feature was the large accumulation of dissolved organic matter (DOM) in the SPG compared to the surrounding waters, in particular dissolved organic carbon (DOC) where concentrations were at levels rarely measured in oceanic waters (>100 µmoles l −1 ). Due to this large pool of DOM in the SPG photic layer, integrated values followed a converse geographical pattern to that of inorganic nutrients with a large accumulation in the centre of the SPG. Whereas suspended particulate matter in the mixed layer had a C/N ratio largely conforming to the Redfield stochiometry (C/N≈6.6), marked deviations were observed in this excess DOM (C/N≈16 to 23). The marked geographical trend suggests that a net in situ source exists, mainly due to biologic...

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Section: Discussionsupporting

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Distribution of inorganic and organic nutrients in the South Pacific Ocean − evidence for long-term accumulation of organic matter in nitrogen-depleted waters

2008

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“…Voyage-specific high-resolution NO 3 À data were derived from a third polynomial correlation between temperature and in situ NO 3 À bottle data [King and Devol, 1979;Kamykowski et al, 2002]. Water mass-specific r 2 for the polynomials for the Leeuwin Current (LC) waters were r 2 = 0.…”

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confidence: 99%

Sources of new nitrogen in the Indian Ocean

Raes

Thompson

McInnes

et al. 2015

Global Biogeochemical Cycles

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Quantifying the different sources of nitrogen (N) within the N cycle is crucial to gain insights in oceanic phytoplankton production. To understand the controls of primary productivity and the associated capture of CO 2 through photosynthesis in the southeastern Indian Ocean, we compiled the physical and biogeochemical data from four voyages conducted in assimilation rates (~530 μmol m À2 h À1 ) relative to NO 3 À assimilation rates (~375 μmol m À2 h À1 ) suggest that the assimilation dynamics of C are primarily regulated by microbial regeneration in our region. N 2 fixation rates did not decline when other source of dissolved inorganic nitrogen were available, although the assimilation of N 2 is a highly energetic process. Our data showed that the diazotrophic community assimilated~2 nmol N L À1 h À1 at relative elevated NH 4 + assimilation rates~12 nmol L À1 h À1 and NO 3 À assimilation rates~6 nmol L À1 h À1 . The small diffusive deep water NO 3 À fluxes could not support the measured NO 3 À assimilation rates and consequently point toward another source of dissolved inorganic NO 3 À . Highest NO 2 À values coincided consistently with shallow lower dissolved O 2 layers (100-200 m; 100-180 μmol L À1 ). These results suggest that nitrification above the pycnocline could be a significant component of the N cycle in the eastern Indian Ocean. In our analysis we provide a conceptual understanding of how NO 3 À in the photic zone could be derived from new N through N 2 fixation. We conclude with the hypothesis that N injected through N 2 fixation can be recycled within the photic zone as NH 4 + and sequentially oxidized to NO 2 À and NO 3 À in shallow lower dissolved oxygen layers.

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“…Estimates of vertical eddy diffusivities, K,, based on the slope of the increase in nitrate with depth in the nitracline and the rate of nitrate uptake measured with 15N (King and Devol 1979;Eppley et al 1979) suggest values off Hawaii of 2.8 + 1.3 cm2. s-l.…”

Section: Multiplyingmentioning

confidence: 99%

High phytoplankton growth and production rates in oligotrophic Hawaiian coastal waters1

Laws

Redalje

Haas³

et al. 1984

Limnology & Oceanography

151

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Estimates of vertical eddy diffusion through the thermocline from phytoplankton nitrate uptake rates in the mixed layer of the eastern tropical Pacific1

Cited by 88 publications

References 13 publications

Distribution of inorganic and organic nutrients in the South Pacific Ocean − evidence for long-term accumulation of organic matter in nitrogen-depleted waters

Distribution of inorganic and organic nutrients in the South Pacific Ocean − evidence for long-term accumulation of organic matter in nitrogen-depleted waters

Sources of new nitrogen in the Indian Ocean

High phytoplankton growth and production rates in oligotrophic Hawaiian coastal waters1

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