Half‐saturation Constants for Uptake of Nitrate and Ammonium by Marine Phytoplankton1

Eppley, Richard W.; Rogers, Jane N.; McCarthy, James J.

doi:10.4319/lo.1969.14.6.0912

Cited by 1,031 publications

(402 citation statements)

References 19 publications

(4 reference statements)

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“…Macronutrients (nitrate and ammonium, phosphate, and silicate) and the micronutrient iron limit phytoplankton growth and thus improve the representation of their dynamics (Aumont et al 2003;Aumont and Bopp 2006). PISCES has two sizes for phytoplankton (nanophytoplankton and diatoms), for which growth is parametrized using the Eppley et al (1969) formulation but limited by external availability of nutrients. Diatoms differ from nanophytoplankton because they need silicon and more iron (Sunda and Huntsman 1997) and because they have higher half-saturation constants due to their larger mean size.…”

Section: Marine Biogeochemistry Model: Piscesmentioning

confidence: 99%

Skill assessment of three earth system models with common marine biogeochemistry

et al. 2012

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We have assessed the ability of a common ocean biogeochemical model, PISCES, to match relevant modern data fields across a range of ocean circulation fields from three distinct Earth system models: IPSL-CM4-LOOP, IPSL-CM5A-LR and CNRM-CM5.1. The first of these Earth system models has contributed to the IPCC 4th assessment report, while the latter two are contributing to the ongoing IPCC 5th assessment report. These models differ with respect to their atmospheric component, ocean subgrid-scale physics and resolution. The simulated vertical distribution of biogeochemical tracers suffer from biases in ocean circulation and a poor representation of the sinking fluxes of matter. Nevertheless, differences between upper and deep ocean model skills significantly point to changes in the underlying model representations of ocean circulation. IPSL-CM5A-LR and CNRM-CM5.1 poorly represent deep-ocean circulation compared to IPSL-CM4-LOOP degrading the vertical distribution of biogeochemical tracers. However, their representations of surface wind, wind stress, mixed-layer depth and geostrophic circulations (e.g., Antarctic Circumpolar Current) have been improved compared to IPSL-CM4-LOOP. These improvements result in a better representation of large-scale structure of biogeochemical fields in the upper ocean. In particular, a deepening of 20-40 m of the summer mixed-layer depth allows to capture the 0-0.5 lgChl L -1 concentrations class of surface chlorophyll in the Southern Ocean. Further improvements in the representation of the ocean mixedlayer and deep-ocean ventilation are needed for the next generations of models development to better simulate marine biogeochemistry. In order to better constrain ocean dynamics, we suggest that biogeochemical or passive tracer modules should be used routinely for both model development and model intercomparisons.

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Section: Marine Biogeochemistry Model: Piscesmentioning

confidence: 99%

Skill assessment of three earth system models with common marine biogeochemistry

et al. 2012

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“…The half saturation constants for the uptake of ammonium and nitrate by phytoplankton were used to tune (optimize) the model. Thus they were set at values, which fall within the ranges reported for the uptake of ammonium and nitrate by phytoplankton at high nutrient concentrations (Collos et al, 2005;Eppley et al, 1969), reflecting the high nitrate and ammonium concentrations found at station CB3.3C throughout much of the year. The half saturation constants were also set so that the uptake affinity for ammonium of small phytoplankton is stronger than that of large phytoplankton (Stolte et al, 1994).…”

Section: Phytoplanktonmentioning

confidence: 99%

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

Keller

Hood

2011

Ecological Modelling

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a b s t r a c tIn this paper we investigate the seasonal autochthonous sources of dissolved organic carbon (DOC) and nitrogen (DON) in the euphotic zone at a station in the upper Chesapeake Bay using a new mass-based ecosystem model. Important features of the model are: (1) carbon and nitrogen are incorporated by means of a set of fixed and varying C:N ratios; (2) dissolved organic matter (DOM) is separated into labile, semi-labile, and refractory pools for both C and N; (3) the production and consumption of DOM is treated in detail; and (4) seasonal observations of light, temperature, nutrients, and surface layer circulation are used to physically force the model. The model reasonably reproduces the mean observed seasonal concentrations of nutrients, DOM, plankton biomass, and chlorophyll a. The results suggest that estuarine DOM production is intricately tied to the biomass concentration, ratio, and productivity of phytoplankton, zooplankton, viruses, and bacteria. During peak spring productivity phytoplankton exudation and zooplankton sloppy feeding are the most important autochthonous sources of DOM. In the summer when productivity peaks again, autochthonous sources of DOM are more diverse and, in addition to phytoplankton exudation, important ones include viral lysis and the decay of detritus. The potential importance of viral decay as a source of bioavailable DOM from within the bulk DOM pool is also discussed. The results also highlight the importance of some poorly constrained processes and parameters. Some potential improvements and remedies are suggested. Sensitivity studies on selected parameters are also reported and discussed.

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“…I hypothesize that cell size is this other factor. Half-saturation constants for nutrient uptake should increase with algal size due to surface-volume considerations (Hudson and Morel 1990), and there is theoretical (Hudson and Morel 1990;Aksnes and Egge 1991) and empirical (Eppley et al 1969;Moloney and Field 1991) evidence that this scaling should be allometric (power law). For ammonium, the allometric dependence of the half-saturation constant K on size can be written…”

Section: Origin Of the Wheeler-kokkinakis Patternmentioning

confidence: 99%

An optimization‐based model of iron—light—ammonium colimitation of nitrate uptake and phytoplankton growth

Armstrong

1999

Limnology & Oceanography

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The ability to model ''new'' (nitrate-based) production is crucial to predicting the ocean's role in the global carbon cycle. The ability to model the distribution of high-nutrient/low-chlorophyll (HNLC) areas is particularly important in this regard. Here I draw together three elements that appear to be necessary for constructing the required model: (1) iron limitation of algal growth rates as an ultimate cause of the HNLC condition; (2) ammonium inhibition of nitrate uptake and utilization as a proximate mechanism that leads to reduced nitrate use; and (3) the dependence of both processes on algal cell size. In the model, cells are postulated to maximize their growth rates by partitioning scarce iron between nitrogen-and carbon-related demands. The effect of iron limitation is postulated to depend on cell size through surface/volume effects on uptake efficiency; this dependence on cell size in turn affects phytoplankton community structure and community-level uptake of nitrate. The efficacy of the model is demonstrated by its ability to reproduce community-level curves of nitrate uptake versus ammonium concentration from both HNLC and non-HNLC areas. The partition formalism can be incorporated directly into ecosystem models; when implemented in an ecosystem model with multiple size classes, the model should produce HNLC versus non-HNLC conditions in appropriate locations and for appropriate reasons. In particular, the model's ability to produce iron-light and iron-light-nitrogen colimitation should be useful in understanding and predicting the HNLC condition in parts of the Southern Ocean. With suitable changes to parameter values, the postulated mechanism for iron partitioning may also prove useful in modeling iron and energy partitioning in nitrogen fixers. The ability to model the distribution of high-nutrient/lowchlorophyll (HNLC) areas, where concentrations of nitrate and phosphate remain high throughout the year, is critical to prognostic studies of the global carbon cycle. Empirical evidence suggests that the ability to model iron limitation of growth and nitrate uptake will be a key element in predicting HNLC conditions. As the prime example, a scarcity of iron has recently been shown to limit phytoplankton growth, biomass accumulation, and size and taxonomic structure in the equatorial Pacific, a major HNLC region (Coale et al. 1996). Addition of iron to surface waters of this region caused a massive phytoplankton bloom and drawdown of nitrate, accompanied by a marked reduction in the fugacity of CO 2 (Cooper et al. 1996). The possibility of similar conversion of the subarctic Pacific (La Roche et al. 1996) and the Southern Ocean (de Baar et al. 1995;Kumar et al. 1995) from HNLC to non-HNLC by the addition of iron is supported by more indirect evidence. AcknowledgmentsConversations with Richard Geider helped greatly in the development of these ideas, particularly in the realization that it could be extremely useful scientifically to have a single model of iron limitation that both biogeochem...

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Half‐saturation Constants for Uptake of Nitrate and Ammonium by Marine Phytoplankton1

Cited by 1,031 publications

References 19 publications

Skill assessment of three earth system models with common marine biogeochemistry

Skill assessment of three earth system models with common marine biogeochemistry

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

An optimization‐based model of iron—light—ammonium colimitation of nitrate uptake and phytoplankton growth

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