Physical and biological controls of nitrate concentrations in the upper subtropical North Pacific Ocean

Ascani, François; Richards, Kelvin J; Firing, Eric; Grant, Scott; Johnson, Kenneth S.; Jia, Yanli; Lukas, Roger; Karl, David M.

doi:10.1016/j.dsr2.2013.01.034

Cited by 50 publications

(69 citation statements)

References 41 publications

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“…The upward nitrate flux problem derives from budgeting analysis that concludes that nitrate introduced at the base of the euphotic zone must be transported upward many 10s of meters to zones of net community production and export (Ascani et al 2013;Johnson et al 2010). In order to assess the potential role of Rhizosolenia mats in the Pacific, and by inference, other migrating phytoplankton, we evaluated this using our new data and previously published models.…”

Section: Significance To Oceanic Nutrient Cyclesmentioning

confidence: 99%

“…Recent observations of isotopic anomalies in phytoplankton groups (Fawcett et al 2011) and unresolved nutrient inputs (Ascani et al 2013;Johnson et al 2010) have focused attention on phytoplankton sinking and ascent, and the role this may be playing in connecting deep nutrient pools with surface productivity. Nutrient budgets are key to constraining the "biological pump", the active removal of CO 2 from the surface ocean to the deep sea by biological processes (DeVries et al 2012).…”

Section: Preprintsmentioning

confidence: 99%

“…However, < 30 µm diameter eukaryotes cells are found with δ 15 N signatures of 4-5 at 30-60 m in the Sargasso Sea, suggesting sub-euphotic zone nitrate is reaching these depths (40+ m above the nutricline) (Fawcett et al 2011). Nitrate budgets using profiling floats and subsequent modeling have indicated that a biological transport of nitrate upward is the most likely mechanism for supply the upper euphotic zone (Ascani et al 2013;Johnson et al 2010) Phytoplankton migrating across this gradient could provide a mechanism for transport via subsurface uptake and subsequent shallow excretion (Singler & Villareal 2005). In the eastern N. Pacific gyre, vertical migration is estimated to account for an average of 14% of new production with maximum values up to 59% (Singler & Villareal 2005;Villareal et al 1999b).…”

Section: Introductionmentioning

confidence: 99%

“…Phytoplankton migrators are clearly transporting N (and presumably P) upward, but the significance of the process in oceanic nutrient budgets was hard to assess due to the limited geographic range of observations and abundance estimates (Emerson & Hayward 1995;Johnson et al 2010). Although this flora is endemic to all warm oceans, their large size and relatively low numbers (~10 0 -10 2 m -3) have made quantification uncommon as research efforts focused on the dominant nano and picoplankton that are 6-7 orders of magnitude more abundant.Recent observations of isotopic anomalies in phytoplankton groups (Fawcett et al 2011) and unresolved nutrient inputs (Ascani et al 2013;Johnson et al 2010) have focused attention on phytoplankton sinking and ascent, and the role this may be playing in connecting deep nutrient pools with surface productivity. Nutrient budgets are key to constraining the "biological pump", the active removal of CO 2 from the surface ocean to the deep sea by biological processes (DeVries et al 2012).…”

mentioning

confidence: 99%

“…Vertical migration is a consistent feature of their biology and occurs across the entire distributional range. A reassessment of the quantitative importance of mat N transport is required and is particularly timely given the urgent need to identify mechanisms capable of closing euphotic zone nitrate budgets (Ascani et al 2013;Johnson et al 2010). In the next section, we will consider the implications for nutrient cycling and the role of ascending motion in general in phytoplankton.…”

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confidence: 99%

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Upward nitrate transport by phytoplankton in oceanic waters: balancing nutrient budgets in oligotrophic seas

Villareal

Pilskaln

Montoya

et al. 2014

Preprint

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In oceanic gyres, primary producers are numerically dominated by small (1-5 µm diameter) pro-and eukaryotic cells that primarily utilize recycled nutrients produced by rapid grazing turnover in a highly efficient microbial loop. Continuous losses of nitrogen to depth by sinking, either as single cells, aggregates or fecal pellets, are balanced by both nitrate inputs at the base of the euphotic zone and nitrogen-fixation. This input of N (new nitrogen) to balance export losses (the biological pump) is a fundamental aspect of nitrogen cycling and central to understanding carbon fluxes in the ocean. In the Pacific Ocean, detailed nitrogen budgets at the time-series station HOT require upward transport of nitrate from the nutricline (80-100 m) into the surface layer (~0-40 m) to balance productivity and export needs. However, concentration gradients are negligible and cannot support the fluxes. Physical processes can inject nitrate into the base of the euphotic zone, but the mechanisms for transporting this nitrate into the surface layer across many 10s of m in highly stratified systems are unknown.In these seas, vertical migration by the very largest 10 2 -10 3 µm diameter) phytoplankton is common as a survival strategy to obtain nitrogen from sub-euphotic zone depths. This vertical migration is driven by buoyancy changes rather than by flagellated movement and can provide upward nitrogen transport as nitrate (mM concentrations) in the cells. However, the contribution of vertical migration to nitrate transport has been difficult to quantify over the required basin scales. In this study, we use towed optical systems and isotopic tracers to PrePrintsIntroduction Nitrogen in the euphotic zone of the open sea has long been recognized to partition into two distinct pools of availability (Dugdale & Goering 1967). New nitrogen represents introduction of N from outside the euphotic zone, either in the form of deep NO 3 -or nitrogenfixation, while regenerated N results from consumption and remineralization of dissolved or particulate N (Dugdale & Goering 1967). While regenerated N dominates the total phytoplankton uptake, new N is critical to balance losses due to vertical fluxes and is linked to total system productivity (Eppley & Peterson 1979). This has been expressed as the f ratio where 'f' = new/total N uptake and ranges from 0-1. On longer time scales, new N input must balance sedimentary losses or the system will experience net losses of nitrogen (Eppley & Peterson 1979). The surface waters of the open ocean are considered low 'f' ratio environments: N and P often occur at nM concentrations, and ammonium is the dominant form taken up by phytoplankton (Lipschultz et al. 1996;Raimbault et al. 2008;Wu et al. 2000). The f ratio increases in the light-limited lower depths of the euphotic zone due to the increased availability of nitrate at the nutricline, thus creating what has been recognized as a two-layered structure (Goldman 1988). This general pattern can be modified in regions of low iron input, where iron ava...

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Section: Significance To Oceanic Nutrient Cyclesmentioning

confidence: 99%

Section: Preprintsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Upward nitrate transport by phytoplankton in oceanic waters: balancing nutrient budgets in oligotrophic seas

Villareal

Pilskaln

Montoya

et al. 2014

Preprint

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Short‐term variability in euphotic zone biogeochemistry and primary productivity at Station ALOHA: A case study of summer 2012

Wilson

Barone

Ascani

et al. 2015

Global Biogeochemical Cycles

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Time-series observations are critical to understand the structure, function, and dynamics of marine ecosystems. The Hawaii Ocean Time-series program has maintained near-monthly sampling at Station ALOHA (22°45′N, 158°00′W) in the oligotrophic North Pacific Subtropical Gyre (NPSG) since 1988 and has identified ecosystem variability over seasonal to interannual timescales. To further extend the temporal resolution of these near-monthly time-series observations, an extensive field campaign was conducted during July-September 2012 at Station ALOHA with near-daily sampling of upper water-column biogeochemistry, phytoplankton abundance, and activity. The resulting data set provided biogeochemical measurements at high temporal resolution and documents two important events at Station ALOHA: (1) a prolonged period of low productivity when net community production in the mixed layer shifted to a net heterotrophic state and (2) detection of a distinct sea-surface salinity minimum feature which was prominent in the upper water column (0-50 m) for a period of approximately 30 days. The shipboard observations during July-September 2012 were supplemented with in situ measurements provided by Seagliders, profiling floats, and remote satellite observations that together revealed the extent of the low productivity and the sea-surface salinity minimum feature in the NPSG.

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Seasonal variability of nutrient concentrations in the Mediterranean Sea: Contribution of Bio‐Argo floats

Fommervault

D’Ortenzio

Mangin³

et al. 2015

JGR Oceans

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In 2013, as part of the French NAOS (Novel Argo Oceanic observing System) program, five profiling floats equipped with nitrate sensors (SUNA‐V2) together with CTD and bio‐optical sensors were deployed in the Mediterranean Sea. At present day, more than 500 profiles of physical and biological parameters were acquired, and significantly increased the number of available nitrate data in the Mediterranean Sea. Results obtained from floats confirm the general view of the basin, and the well‐known west‐to‐east gradient of oligotrophy. At seasonal scale, the north western Mediterranean displays a clear temperate pattern sustained by both deep winter mixed layer and shallow nitracline. The other sampled areas follow a subtropical regime (nitracline depth and mixed layer depth are generally decoupled). Float data also permit to highlight the major contribution of high‐frequency processes in controlling the nitrate supply during winter in the north western Mediterranean Sea and in altering the nitrate stock in subsurface in the eastern basin.

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Physical and biological controls of nitrate concentrations in the upper subtropical North Pacific Ocean

Cited by 50 publications

References 41 publications

Upward nitrate transport by phytoplankton in oceanic waters: balancing nutrient budgets in oligotrophic seas

Upward nitrate transport by phytoplankton in oceanic waters: balancing nutrient budgets in oligotrophic seas

Short‐term variability in euphotic zone biogeochemistry and primary productivity at Station ALOHA: A case study of summer 2012

Seasonal variability of nutrient concentrations in the Mediterranean Sea: Contribution of Bio‐Argo floats

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