Sources of new nitrogen in the Indian Ocean

Raes, Eric J.; Thompson, Peter A.; McInnes, Alison; Nguyễn, Hải Thủy; Hardman-Mountford, Nick J.; Waite, Anya M.

doi:10.1002/2015gb005194

Cited by 22 publications

(23 citation statements)

References 99 publications

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“…The mean difference in the mixed layer depth calculated using two independent criteria (the water depth at which vertical gradients in density and temperature become Δσ θ = 0.03 kg/m 3 and Δt = 0.2°C, respectively) resulted in a difference of ±0.1 Pg C per 8 months. Uncertainty associated with the horizontal C T flux depends on uncertainties about current velocities (assumed to be ±50% error, based on Quay & Stutsman, 2003) and the horizontal nC T gradient among pixels (±25%, estimated in this study from the fit between nC T and latitude or longitude). In combination, these uncertainties accounted for a difference of ±0.06 Pg C per 8 months in our global NCP N2fix estimate.…”

Section: Results and Error Analysismentioning

confidence: 98%

“…In the oligotrophic ocean, N limitation is ameliorated by a diverse assemblage of diazotrophs, which reduce strongly bonded N 2 to ammonia and dissolved organic nitrogen (DON) via an energy intensive process of N 2 fixation (Capone et al, 1997;Karl et al, 2002). This process is known to be a major source of N to the oligotrophic ocean, accounting for approximately 50% of the total external source of N (Galloway et al, 2004;Gruber & Galloway, 2008;Raes et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

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Carbon‐Based Estimate of Nitrogen Fixation‐Derived Net Community Production in N‐Depleted Ocean Gyres

Lee

Takahashi

et al. 2018

Global Biogeochemical Cycles

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Accurate estimation of net community production (NCP) in the ocean is important for determining the future trend for carbon dioxide concentrations in the atmosphere and thus for understanding the global carbon cycle and climate change. Most methods for measuring NCP rely on analysis of dissolved fixed inorganic nitrogen species (N), which are believed to be limiting factors for NCP. However, in the vast areas of the ocean gyres only low levels of N are available for phytoplankton during much of the year. In this study the NCP was estimated by summing the seasonal reduction in the concentration of dissolved inorganic carbon (CT) in the surface mixed layer, corrected for changes associated with salinity variation, net air‐sea CO2 flux, horizontal C advection, non‐Redfield diffusive C and N fluxes (deviations from the C:N ratio of 7), and anthropogenic nitrogen deposition. The mixed layer reduction in CT was calculated from an annual CT cycle, deduced from comprehensive records of surface pCO2 and total alkalinity, using an established thermodynamic model. This method yielded a value of 0.6 ± 0.2 Pg of C, which represents the NCP that occurred during the warming period (approximately 8 months) in the nitrate‐depleted (<0.2 μmol/kg) ocean. Our estimate is broadly consistent with the global N2 fixation rate estimated using the 15N‐based method and suggests that N2 fixation by microorganisms is a major driver for this NCP.

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Section: Results and Error Analysismentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Carbon‐Based Estimate of Nitrogen Fixation‐Derived Net Community Production in N‐Depleted Ocean Gyres

Lee

Takahashi

et al. 2018

Global Biogeochemical Cycles

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“…Regardless, the low δ 15 N (“oceanic”) individuals appeared to consistently depend on prey supported by nitrogen fixation (e.g., Raes et al. ) over months to years prior to sampling, perhaps in the central Pacific gyre where mid‐water particle δ 15 N values are at their minimum of close to −2‰ (Somes et al. ).…”

Section: Discussionmentioning

confidence: 99%

“…Evidence of TPs averaging markedly less than 3 (i.e., 2.4 AE 1) could suggest significant ingestion, incidental or otherwise, of phytoplankton or algal debris (e.g., herbivory; see Rohner et al [2013] and Leigh et al [2018]) but could also reflect the uncertainty in, or an overestimation of, D 15 N Glu-Phe . Regardless, the low d 15 N ("oceanic") individuals appeared to consistently depend on prey supported by nitrogen fixation (e.g., Raes et al 2015) over months to years prior to sampling, perhaps in the central Pacific gyre where mid-water particle d 15 N values are at their minimum of close to À2& (Somes et al 2010). This mid-ocean region is perhaps the only location with d 15 N low enough to explain the estimates of prey around 2& (Fig.…”

Section: Rhincodon Typus Foraging Specialization From Metabolically Cmentioning

confidence: 98%

Enhancing insights into foraging specialization in the world's largest fish using a multi‐tissue, multi‐isotope approach

Wyatt

Matsumoto

Chikaraishi

et al. 2019

Ecological Monographs

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Intra‐species variability in foraging strategies may be common, which has significant implications for efforts to understand and manage enigmatic species like the whale shark Rhincodon typus. The ecological relevance of differences in tissue isotopes within and between individuals in the context of foraging however depends on understanding tissue turnover times and carbon (Δ13C) and nitrogen (Δ15N) discrimination, which can vary with physiology, metabolism, and diet quality. Here, we examine isotope dynamics in captive R. typus as a basis for enhanced ecological insights into wild populations of the world's largest fish and other enigmatic species. A variable diet, principally consisting of two krill (Euphausia pacifica and Euphausia superba) provided an average of 48 ± 20 MJ/d (mean ± SD), or 2.7 ± 1.3 times basal metabolic requirements. On this diet, in agreement with allometric relationships, large body sizes (3,000–4,000 kg) were matched by slow plasma and cartilage turnover rates (empirically derived as 9 months and 3 yr, respectively), which provide tissue‐specific limits on the timescales over which we can isotopically detect diet changes in this species. Average diet‐to‐tissue discrimination showed significant variation between tissues (plasma and cartilage), and among growing and fasting individuals (Δ13C range, 1.5 to 5.5‰; Δ15N range, −0.1 to 2.9‰). Assimilation rates increased with temperature and were higher for the smaller E. pacifica (15 ± 2 mm) than E. superba (48 ± 2 mm). Growth significantly lowered both Δ15Nplasma and Δ15Ncartilage, with inappetence markedly reducing Δ15Nplasma and Δ13Cplasma, as well as significantly altering blood biochemistry. Captive findings facilitated the first robust multi‐tissue growth‐ and nutrition‐corrected isotope analysis of a wild R. typus population, suggesting individual foraging specialization on low trophic level mid‐ocean or coastal prey. Long‐term fasting during ocean‐basin‐scale migrations may be common and such metabolic effects should be carefully quantified when isotopically assessing intra‐species foraging differences. The metabolically constrained multi‐tissue, multi‐isotope approach described can facilitate ecological insights that are indispensable for effective conservation and management of globally threatened, but poorly understood, species by identifying differences in key foraging areas and target prey within and between individuals.

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“…NO 3 À : PO 4 3À ratio is ,4 AE 2. This is far below the Redfield ratio (Redfield 1958), indicating strong nitrate limitation for primary production Raes et al 2015).…”

Section: Oceanographymentioning

confidence: 87%

Baseline biogeochemical data from Australia's continental margin links seabed sediments to water column characteristics

Radke

Nicholas

Thompson

et al. 2017

Mar. Freshwater Res.

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Abstract. Surficial marine sediments are an important source of nutrients for productivity and biodiversity, yet the biogeochemistry of these sediments is poorly known in Australia. Seabed samples were collected at .350 locations in Australia's western, northern and eastern continental margins during Federal Government surveys . Parameters analysed included measures of organic matter (OM) source (d 13 C, d 15 N and C : N ratios), concentration (percentage total organic carbon, %TOC, and surface area-normalised TOC, OC : SA) and bioavailability (chlorin indices, total reactive chlorins, total oxygen uptake, total sediment metabolism (TSM), sediment oxygen demand (SOD) and SOD and TSM normalised against TOC). The aim of the present study was to summarise these biogeochemical 'baseline' data and make contextualised inferences about processes that govern the observed concentrations. The OM was primarily from marine sources and the OC : SA broadly reflected water column productivity (based on Moderate Resolution Imaging Spectroradiometer, MODIS). Approximately 40% of sediments were organic poor by global standards, reflecting seawater oligotrophy; ,12% were organic rich due to benthic production, high water column productivity and pockmark formation. OM freshness varied due to pigment degradation in water columns and dilution with refractory OM in reworked sediments. d 15 N values confirmed the importance of N 2 fixation to Timor Sea productivity, and point to recycling of fixed nitrogen within food chains in Western Australia.

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Sources of new nitrogen in the Indian Ocean

Cited by 22 publications

References 99 publications

Carbon‐Based Estimate of Nitrogen Fixation‐Derived Net Community Production in N‐Depleted Ocean Gyres

Carbon‐Based Estimate of Nitrogen Fixation‐Derived Net Community Production in N‐Depleted Ocean Gyres

Enhancing insights into foraging specialization in the world's largest fish using a multi‐tissue, multi‐isotope approach

Baseline biogeochemical data from Australia's continental margin links seabed sediments to water column characteristics

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