Darren R. Clark

Darren R. Clark
Plymouth Marine Laboratory | PML

About

50
Publications
10,394
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1,820
Citations
Citations since 2017
19 Research Items
678 Citations
2017201820192020202120222023020406080100120
2017201820192020202120222023020406080100120
2017201820192020202120222023020406080100120
2017201820192020202120222023020406080100120

Publications

Publications (50)
Article
Full-text available
The Lagrangian progression of a biological community was followed in a filament of the Mauritanian upwelling system, north-west Africa, during offshore advection. The inert dual tracers sulfur hexafluoride and helium-3 labelled a freshly upwelled patch of water that was mapped for 8 days. Changes in biological, physical, and chemical characteristic...
Article
Full-text available
N regeneration was measured on a transect of the North and South Atlantic, from the United Kingdom to the Falkland Islands, that included extreme oligotrophic conditions. NH4+ and NO2- oxidation rates were measured from the surface and base of the photic zone at 16 stations, using an isotope dilution technique in conjunction with gas chromatography...
Article
Full-text available
The flux of organic material sinking to depth is a major control on the inventory of carbon in the ocean. To first order, the oceanic system is at equilibrium such that what goes down must come up. Because the export flux is difficult to measure directly, it is routinely estimated indirectly by quantifying the amount of phytoplankton growth, or pri...
Article
Full-text available
Coccolithophorids are enigmatic plankton that produce calcium carbonate coccoliths, which over geological time have buried atmospheric CO 2 into limestone, changing both the atmosphere and geology of the Earth. However , the role of coccoliths for the proliferation of these organisms remains unclear; suggestions include roles in anti-predation, enh...
Article
Full-text available
The recycling of scarce nutrient resources in the sunlit open ocean is crucial to ecosystem function. Nitrification directs ammonium (NH4+) derived from organic matter decomposition towards the regeneration of nitrate (NO3-), an important resource for photosynthetic primary producers. However, the technical challenge of making nitrification rate me...
Article
Full-text available
(1) Rapid virus proliferation can strongly control phytoplankton host populations, playing a significant role in marine biogeochemistry and ecology. We explore how marine lytic viruses impact phytoplankton succession affecting host and non‐host populations. (2) Using an in silico food‐web we conducted simulation experiments under a range of differe...
Article
Full-text available
Human activities are changing the Arctic environment at an unprecedented rate resulting in rapid warming, freshening, sea ice retreat and ocean acidification of the Arctic Ocean. Trace gases such as nitrous oxide (N2O) and methane (CH4) play important roles in both the atmospheric reactivity and radiative budget of the Arctic and thus have a high p...
Preprint
Full-text available
The recycling of scarce nutrient resources in the sunlit open ocean is crucial to ecosystem function. Ammonium oxidation, the first stage of the nitrification process, directs ammonium derived from organic matter decomposition towards the regeneration nitrate, an important resource for photosynthetic primary producers. However, the technical challe...
Article
Full-text available
Fishing activities continue to decimate populations of marine mammals, fish, and their habitats in the coastal waters of the Kep Archipelago, a cluster of tropical islands on the Cambodia-Vietnam border. In 2019, the area was recognized as an Important Marine Mammal Area, largely owing to the significant presence of Irrawaddy dolphins (Orcaella bre...
Article
A mechanistic system dynamics description is developed of the interactions between a single lytic-virus – phytoplankton-host couple. The model has state variables for virus, uninfected and infected host biomass, and describes virus and host allometry and physiology. The model, analogous to experimental laboratory virus-host systems but more amenabl...
Article
Full-text available
Estimates of oceanic emissions of nitrous oxide (N2O) are surrounded by a considerable degree of uncertainty, particularly regarding the contribution of productive shelf regions, where assessments are based on limited observations. In this paper, we have applied a coupled hydrodynamic-biogeochemical model resolving N2O dynamics to estimate N2O emis...
Article
Full-text available
Physical and chemical characteristics of the marine environment are responding to climate change induced by anthropogenic activities. It is almost certain that the rate of change will accelerate over the coming decades in the absence of dramatic and immediate mitigation efforts. Existing evidence indicates that among these changes, global seawater...
Article
Full-text available
Observations made within a cold filament in the Mauritanian upwelling system demonstrate that intense submesoscale circulations at the peripheral edges of the filament are likely responsible for anomalously high levels of observed primary productivity by resupplying nutrients to the euphotic zone. Measurements made on the shelf within the recently...
Data
Appendix 1. Model description. (DOCX)
Article
Full-text available
The capacity of bacteria for degrading dissolved organic nitrogen (DON) and remineralising ammonium is of importance for marine ecosystems, as nitrogen availability frequently limits productivity. Here, we assess the capacity of a widely distributed and metabolically versatile marine bacterium to degrade phytoplankton-derived dissolved organic carb...
Article
Once fixed by photosynthesis carbon becomes part of the marine food web. The fate of this carbon has two possible outcomes, it may be respired and released back to the ocean and potentially to the atmosphere as CO 2 or retained in the ocean interior and/or marine sediments for extended time scales. The most important biologically mediated processes...
Article
Full-text available
The lagrangian progression of biogeochemical processes was followed in a filament of the Mauritanian upwelling system, North West Africa, during offshore advection. Inert duel tracers sulphur hexafluoride and helium-3 labelled a freshly upwelled patch of water that was mapped for 8 days. Changes in biological, physical and chemical characteristics...
Poster
Full-text available
The oligotrophic oceans are characterised by extremely low nutrient concentrations which constrain the rate and extent of primary productivity. It is likely that in these systems microbial processes associated with nutrient utilisation and regeneration are very tightly coupled and that nutrient recycling is highly efficient. A characteristic featur...
Article
Full-text available
Human activity causes ocean acidification (OA) though the dissolution of anthropogenically generated CO 2 into seawater, and eutrophication through the addition of inorganic nutrients. Eutrophication increases the phytoplankton biomass that can be supported during a bloom, and the resultant uptake of dissolved inorganic carbon during photosynthesis...
Article
Full-text available
The assimilation and regeneration of dissolved inorganic nitrogen, and the concentration of N 2 O, was investigated at stations located in the NW European shelf sea during June/July 2011. These observational measurements within the photic zone demonstrated the simultaneous regeneration and assimilation of NH + 4 , NO − 2 and NO − 3 . NH + 4 was ass...
Article
The combined consequences of the multi-stressors of pH and nutrient availability upon the growth of a marine diatom were investigated. Thalassiosira weissflogii was grown in N- or P-limited batch culture in sealed systems, with pH commencing at 8.2 (extant conditions) or 7.6 (ocean acidification [OA] conditions), and then pH was allowed to either d...
Article
Full-text available
The impact of light and nutrients (such as silicate and iron) availability on nitrogen uptake and primary production vary seasonally and regionally in the Southern Ocean. The seasonal cycle of nitrogen uptake by phytoplankton in the Southern Ocean is not fully resolved over an annual scale due to the lack of winter in situ measurements. In this stu...
Article
Full-text available
The assimilation and regeneration of dissolved inorganic nitrogen, and the concentration of N2O, was investigated at stations located in the NW European shelf sea during June/July 2011. These observational measurements within the photic zone demonstrated the simultaneous regeneration and assimilation of NH4+, NO2- and NO3-. NH4+ was assimilated at...
Article
Full-text available
Anthropogenically released CO2 is dissolving in the ocean, causing a decrease in bulk-seawater pH (ocean acidification). Projections indicate that the pH will drop 0.3 units from its present value by 2100 (ref. 1). However, it is unclear how the growth of plankton is likely to respond. Using simulations we demonstrate how pH and carbonate chemistry...
Article
Full-text available
Anthropogenically released CO2 is dissolving in the ocean, causing a decrease in bulk-seawater pH (ocean acidification). Projections indicate that the pH will drop 0.3 units from its present value by 2100 (ref. ). However, it is unclear how the growth of plankton is likely to respond. Using simulations we demonstrate how pH and carbonate chemistry...
Article
Full-text available
Concentrations of dissolved nitrous oxide (N2O) and N2O flux densities were determined during the Lagrangian investigation of two filaments advected from the Mauritanian upwelling. The ratio between remineralization and N2O production, predominantly through nitrification was 0.11 ± 0.01%. This was linked to the hydrodynamic character of each filame...
Article
N-regeneration and N-assimilation rates were investigated in surface waters of the Iberian Peninsula, northeast Atlantic, during a period of seasonal upwelling. Stations were selected on the basis of near-real-time remotely sensed data to provide a contrast between upwelling and oligotrophic conditions. Inorganic nitrogen (NO(3)(-) and NH(4)(+)) wa...
Article
Three models describing dissolved organic matter (DOM) flux and phytoplankton death, each of different levels of complexity, were constructed and tested against experimental data for a cyanobacterium, a chlorophyte, two diatoms, two dinoflagellates, and two prymnesiophytes. The simplest model described only bulk carbon (C) and nitrogen (N) forms of...
Article
Full-text available
The flux of organic material sinking to depth is a major control on the inventory of carbon in the ocean. To first order, the oceanic system is at equilibrium such that what goes down must come up. Because the export flux is difficult to measure directly, it is routinely estimated indirectly by quantifying the amount of phytoplankton growth, or pri...
Article
An isotope dilution method has been developed to determine by gas chromatography/mass spectrometry (GC/MS) the rates of ammonium and nitrite oxidation in severely oligotrophic marine waters. The method is based on the formation of sudan-1 from nitrite, or from nitrate following reduction to nitrite. Samples were collected by solid phase extraction...
Article
A method has been developed for the determination of ammonium concentration and isotopic enrichment in seawater samples at the low nanomolar range (10–100 nmol/kg). It is based on the reaction of phenol/hypochlorite with ammonium to form indophenol, with subsequent solid phase extraction, derivatisation and analysis by Gas Chromatography Mass Spect...
Article
Summary • The ability of the diatom Thalassiosira weissflogii to assimilate inorganic N in darkness is compared with that seen in flagellates. • Experiments were conducted with T. weissflogii grown in N-replete and in N-limiting cultures and the rates and capacity for ammonium and nitrate assimilation were determined. • High daily growth rates in t...
Article
Summary • Alternative strategies for the dark assimilation of ammonium and nitrate into microalgae are explored using a mechanistic model of algal physiology. • The standard diatom strategy, continuation of N assimilation at high rates in darkness as long as reserve C remains, is the most advantageous. The flagellate strategy, incorporating ammoniu...
Article
The capabilities of the diel vertically migrating flagellate Heterosigma carterae Hulburt for assimilating ammonium and nitrate into cell-N in light and in darkness were studied using cells of different N-status. Ammonium utilization in darkness, except by N-replete cells, attained>50% of use in the light. However, the capacity to use nitrate was p...
Article
The growth of the marine flagellate Isochrysis galbana was followed in batch cultures at four concentrations of dissolved inorganic carbon (DIC), from C- and N-replete lag phase into C- and/or N-deplete stationary phase. Organic buffers were omitted from the growth medium, and culture pH was maintained at 8.30±0.05 by the addition of acid or alkali...
Article
The abundance of various mesozooplankon taxa was measured in the NE Atlantic (36–64°N and 15–24°W) during June and July 1996 using a high-speed plankton sampler, the U-Tow. A total of 225 plankton samples were collected, each representing about 16.5km of tow. The abundance of mesozooplankton during 1996 was compared to the data that have been colle...
Article
The growth of two species of marine diatom, Thalassiosira weissflogii (Grunow) and Thalassiosira pseudonana (Hustedt), was followed in batch cultures at four concentrations of dissolved inorganic carbon from N- and C-replete lag phase into N- and/or C-deplete stationary phase. Results describe the relationship between carbon-specific growth rate (μ...
Article
Full-text available
Zooplankton samples were collected by a high speed sampler, the U-Tow, in the north-east Atlantic between 61.6 and 36.7°N during June and July 1996, and were used to examine the causality of spatial distributions along a 4000 km transect. Peak zooplankton abundance and biovolume estimations were associated with a frontal system at 48–52°N, which se...
Article
Full-text available
A range of marine phytoplankton was grown in closed systems in order to investigate the kinetics of dissolved inorganic carbon (DIC) use and the influence of the nitrogen source under conditions of constant pH. The kinetics of DIC use could be described by a rectangular hyperbolic curve, yielding estimations of KG(DIC) (the half saturation constant...

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Projects (2)
Project
To test, develop and validate new Earth Observation approaches to quantify input of marine plastic debris through rivers into the coastal areas of developing nations.