Euphotic zone nitrification in the California Current Ecosystem

Stephens, Brandon M.; Wankel, Scott D.; Beman, J. Michael; Rabines, Ariel; Allen, Andrew E.; Aluwihare, Lihini I.

doi:10.1002/lno.11348

Cited by 16 publications

(18 citation statements)

References 82 publications

(175 reference statements)

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“…This was calculated using trapezoidal integration of two values in the lower euphotic zone, potentially introducing error into the estimates; however, this error is likely minimal as values were integrated over a narrow depth range and nitrification decreases exponentially with depth below the euphotic zone. Estimates of the contribution of nitrification to phytoplankton N demand in this study are consistent with values previously reported for the CC system (6–36%; Wankel et al 2007; Stephens et al 2019). The higher contribution of nitrification to the euphotic zone nitrate reservoir in fall suggests that regenerated production is of greater importance during weak upwelling when both primary production and new production are expected to be at a minimum, consistent with a meta‐analysis of nitrification and primary production rates that found an inverse relationship between primary production and the fraction of phytoplankton N demand supplied by nitrification (Peng et al 2018).…”

Section: Discussionsupporting

confidence: 92%

“…Many studies report measurable rates of marine nitrification in the euphotic zone (Ward 2005; Clark et al 2007; Peng et al 2018), and nitrification is increasingly considered an important source of nitrate fueling primary production in the surface ocean (Yool et al 2007; Stephens et al 2019). Nitrification is often thought to be inhibited by light and to only occur in waters below the euphotic zone (Merbt et al 2012).…”

Section: Figmentioning

confidence: 99%

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Nitrification and nitrous oxide dynamics in the Southern California Bight

Laperriere

Morando

Capone

et al. 2020

Limnology & Oceanography

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The amount of primary production fueled by upwelled “new” nitrate can be used to estimate the amount of organic carbon available for export to the deep ocean. Nitrate production in the euphotic zone from the microbial process of nitrification affects these estimates, yet the controls on nitrification in the upper ocean are debated. This study examines how seasonal cycles in primary production influence rates of nitrification fueled by both ammonia and urea‐derived nitrogen (N), and how these processes relate to the distribution of the greenhouse gas nitrous oxide (N2O) using monthly rate measurements from the San Pedro Ocean Time‐series (SPOT) station. Nitrification rates were highest at the onset of upwelling and were correlated with depth‐integrated primary production in the lower euphotic zone. Similar ammonia and urea‐derived N oxidation rates suggest urea is a significant N source fueling nitrification, particularly below the euphotic zone. Nitrification supplied a large proportion of phytoplankton N demand in the lower euphotic zone, implying significant regenerated production. The Southern California Bight was always a source of N2O to the atmosphere, which likely was advected into the system from the eastern tropical North Pacific, rather than produced locally from nitrification, and ventilated to the atmosphere during upwelling. Together, the results suggest the coupling of N remineralization and primary production in the upper ocean have important implications for the amount of organic carbon available for export out of the surface ocean, but that transport may dominate over local production in explaining local N2O dynamics.

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Section: Discussionsupporting

confidence: 92%

Section: Figmentioning

confidence: 99%

Nitrification and nitrous oxide dynamics in the Southern California Bight

Laperriere

Morando

Capone

et al. 2020

Limnology & Oceanography

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“…New production was then computed as primary productivity/6.625 × f‐ratio. New production measurements based on 15

N O_{3}^{-}

uptake can overestimate true nitrate uptake if substantial euphotic zone nitrification occurs, although this issue appears to be minor in the CCE (Stephens et al., 2020; Yool et al., 2007) Sinking carbon vertical fluxes were measured using 238 U − 234 Th disequilibrium and surface‐tethered drifting sediment traps positioned at the base of the euphotic zone (Stukel & Barbeau, 2020; Stukel et al., 2019). Sinking particle flux was typically measured 20–40 m beneath the depth of the euphotic zone.…”

Section: Data Set and Methodsmentioning

confidence: 99%

“…Previous studies in the CCE have shown that new production (i.e., production based on upwelled nitrate) tends to exceed carbon exported vertically below the euphotic zone in the nearshore region, where new and primary production is maximal (Chavez et al., 1991; Kranz et al., 2020; Plattner et al., 2005; Stukel et al., 2011). This imbalance is reduced and possibly compensated further offshore (Stephens et al., 2020; Stukel et al., 2011), with lower than expected vertical carbon export close to shore and higher than expected vertical carbon export further offshore. A hypothesis that would explain this spatial imbalance is that inorganic carbon is fixed in the nearshore region and then exported by the cross‐shore circulation from nearshore sites of production to offshore sites of export.…”

Section: Introductionmentioning

confidence: 99%

Cross‐Shore Flow and Implications for Carbon Export in the California Current Ecosystem: A Lagrangian Analysis

et al. 2021

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In Eastern boundary upwelling systems (EBUS), winds blow alongshore during the upwelling season, causing nutrient-replete deep waters to come to the euphotic zone through divergence of Ekman transport at the coast, stimulating elevated net primary production (NPP) and inorganic carbon uptake. This primary production induces secondary production, the recycling of nutrients, and export of organic carbon into the aphotic zone. EBUSs are strongly advective systems: Ekman currents, as well as intense geostrophic mesoscale eddies and filaments, transport nearshore surface water offshore. The transport of organic matter (OM) from formation sites to export sites, occurs in three-dimensional space: the location of carbon export may be offset spatially from the region of elevated PP (

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“…Generally, nitrification in the surface layer is limited by the photoinhibition of nitrifying microorganisms and competition with phytoplankton for ammonia (Lomas and Lipschultz, 2006). Several studies have suggested the possibility of nitrification within the euphotic zone (Wankel et al, 2007;Rafter and Sigman, 2016;Stephens et al, 2020). Therefore, DN 2 O-AOU and NO − 3 correlations suggested that the slightly supersaturated N 2 O of the surface layer during this investigation may be due to the products derived from nitrification within the euphotic zone, and gradually increasing nitrification near the boundary of the euphotic zone.…”

Section: Hydrographic Conditions In the Stwnpomentioning

confidence: 99%

Distribution and Production of N2O in the Subtropical Western North Pacific Ocean During the Spring of 2020

et al. 2022

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Nitrous oxide (N2O) is an important greenhouse gas emitted in significant volumes by the Pacific Ocean. However, the relationship between N2O dynamics and environmental drivers in the subtropical western North Pacific Ocean (STWNPO) remains poorly understood. We investigated the distribution of N2O and its production as well as the related mechanisms at the surface (0–200 m), intermediate (200–1500 m), and deep (1500–5774 m) layers of the STWNPO, which were divided according to the distribution of water masses. We applied the transit time distribution (TTD) method to determine the ventilation times, and to estimate the N2O equilibrium concentration of water parcels last in contact with the atmosphere prior to being ventilated. In the surface layer, biologically derived N2O (ΔN2O) was positively correlated with the apparent oxygen utilization (AOU) (R2 = 0.48), suggesting that surface N2O may be produced by nitrification. In the intermediate layer, ΔN2O was positively correlated with AOU and NO3− (R2 = 0.92 and R2 = 0.91, respectively) and negatively correlated with nitrogen sinks (N*) (R2 = 0.60). Hence, the highest ΔN2O value in the oxygen minimum layer suggested N2O production through nitrification and potential denitrification (up to 51% and 25% of measured N2O, respectively). In contrast, the deep layer exhibited a positive correlation between ΔN2O and AOU (R2 = 0.92), suggesting that the N2O accumulation in this layer may be caused by nitrification. Our results demonstrate that the STWNPO serves as an apparent source of atmospheric N2O (mean air−sea flux 2.0 ± 0.3 μmol m-2 d-1), and that nitrification and potential denitrification may be the primary mechanisms of N2O production in the STWNPO. We predict that ongoing ocean warming, deoxygenation, acidification, and anthropogenic nitrogen deposition in the STWNPO may elevate N2O emissions in the future. Therefore, the results obtained here are important for elucidating the relationships between N2O dynamics and environmental changes in the STWNPO and the global ocean.

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Euphotic zone nitrification in the California Current Ecosystem

Cited by 16 publications

References 82 publications

Nitrification and nitrous oxide dynamics in the Southern California Bight

Nitrification and nitrous oxide dynamics in the Southern California Bight

Cross‐Shore Flow and Implications for Carbon Export in the California Current Ecosystem: A Lagrangian Analysis

Distribution and Production of N2O in the Subtropical Western North Pacific Ocean During the Spring of 2020

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