Photochemical vs. Bacterial Control of H2O2 Concentration Across a pCO2 Gradient Mesocosm Experiment in the Subtropical North Atlantic

Hopwood, Mark J.; Riebesell, Ulf; Arı́stegui, Javier; Ludwig, Andrea; Achterberg, Eric P.; Hernández, Nauzet

doi:10.3389/fmars.2018.00105

Cited by 5 publications

(14 citation statements)

References 51 publications

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“…Different pCO 2 levels were applied to each mesocosm in a random distribution: the gradient spanned from 400 µatm (the present-day level in the atmosphere and sea surface) up to 1450 µatm (simulating a future scenario of an acidified surface ocean). We chose the following four mesocosms for our study: M5, M6, M7, and M8 with target pCO 2 levels of 400, 1450, 700, and 1150 µatm, respectively, although actual values varied during the different phases of the experiment (see Hopwood et al, 2018).…”

Section: Experimental Design and Samplingmentioning

confidence: 99%

“…Over the last days (t25-t29), the sampling shifted again to every 2nd day (phase II: t18-t29). A wide variety of measurements were carried out in the mesocosms to study the effects of acidification on both ecological and biogeochemical processes (see Hopwood et al, 2018, for additional information on the water samplers and set up of the experiment).…”

Section: Experimental Design and Samplingmentioning

confidence: 99%

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Plankton Community Respiration and ETS Activity Under Variable CO2 and Nutrient Fertilization During a Mesocosm Study in the Subtropical North Atlantic

et al. 2018

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The enzymatic electron transport system (ETS) assay is frequently used as a proxy of respiratory activity in planktonic communities. It is thought to estimate the maximum overall activity of the enzymes associated with the respiratory ETS systems in both eukaryotic and prokaryotic organisms. Thus, in order to derive actual respiration rates (R) from ETS it is necessary to determine empirical R/ETS conversion algorithms. In this study we explore the temporal development of R and ETS activity in natural plankton communities (from bacteria to large phytoplankton) enclosed in mesocosms, treated with different CO 2 concentrations. The experiment lasted 30 days, during which abrupt changes in community structure and biomass occurred through a sharp transition from oligotrophy (phase I) to highly eutrophic conditions (phase II) after nutrient-induced fertilization (day 18). R and ETS did not show any response to CO 2 under oligotrophic conditions, but R increased significantly more in the two high CO 2 mesocosms after fertilization, coinciding with a sharp rise in large phytoplankton (mostly diatoms). R and ETS were significantly correlated only during the eutrophic phase. The R/ETS ranged more than threefold in magnitude during the experiment, with phase-averaged values significantly higher under oligotrophic conditions (0.7-1.1) than after nutrient fertilization (0.5-0.7). We did not find any significant relationship between R/ETS and community structure or biomass, although R correlated significantly with total biomass after fertilization in the four mesocosms. Multiple stepwise regression models show that large phytoplankton explains most of the variance in R during phases I (86%) and II (53%) and of ETS (86%) during phase II, while picophytoplankton contributes up to 73% to explain the variance in the ETS model during phase I. Our results suggest that R/ETS may be too variable in the ocean as to apply constant values to different communities living under contrasting environmental conditions. Controlled experiments with natural communities, like the present one, would help to constrain the range of variability of the R/ETS ratio, and to understand the factors driving it.

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Section: Experimental Design and Samplingmentioning

confidence: 99%

Section: Experimental Design and Samplingmentioning

confidence: 99%

Plankton Community Respiration and ETS Activity Under Variable CO2 and Nutrient Fertilization During a Mesocosm Study in the Subtropical North Atlantic

et al. 2018

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“…"DOC": dissolved organic carbon (glucose); "XRF": X-ray fluorescence spectroscopy. Designs are outlined in Hopwood et al (2020). A diluted Fe(II) stock solution (1-2 µM) was prepared daily.…”

Section: Trace Elementsmentioning

confidence: 99%

“…Concentrations of both DFe and H 2 O 2 (as per Hopwood et al, 2020) were measured at the highest resolution for the baseline treatments (no DOC addition, no zooplankton addition) during the mesocosm experiments. For MesoPat (Fig.…”

Section: General Trends In Fe Biogeochemistry; the Mesoarc And Mesopamentioning

confidence: 99%

Fe(II) stability in coastal seawater during experiments in Patagonia, Svalbard, and Gran Canaria

et al. 2020

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The speciation of dissolved iron (DFe) in the ocean is widely assumed to consist almost exclusively of Fe(III)-ligand complexes. Yet in most aqueous environments a poorly defined fraction of DFe also exists as Fe(II), the speciation of which is uncertain. Here we deploy flow injection analysis to measure in situ Fe(II) concentrations during a series of mesocosm/microcosm/multistressor experiments in coastal environments in addition to the decay rate of this Fe(II) when moved into the dark. During five mesocosm/microcosm/multistressor experiments in Svalbard and Patagonia, where dissolved (0.2 µm) Fe and Fe(II) were quantified simultaneously, Fe(II) constituted 24 %-65 % of DFe, suggesting that Fe(II) was a large fraction of the DFe pool. When this Fe(II) was allowed to decay in the dark, the vast majority of measured oxidation rate constants were less than calculated constants derived from ambient temperature, salinity, pH, and dissolved O 2 . The oxidation rates of Fe(II) spikes added to Atlantic seawater more closely matched calculated rate constants. The difference between observed and theoretical decay rates in Svalbard and Patagonia was most pronounced at Fe(II) concentrations < 2 nM, suggesting that the effect may have arisen from organic Fe(II) ligands. This apparent enhancement of Fe(II) stability under post-bloom conditions and the existence of such a high fraction of DFe as Fe(II) challenge the assumption that DFe speciation in coastal seawater is dominated by ligand bound-Fe(III) species. John, 2014), hydrothermal (Tagliabue et al., 2010;Resing et al., 2015) and shelf sources (Elrod et al., 2004;Severmann Published by Copernicus Publications on behalf of the European Geosciences Union. teams assisting with all aspects of experiment logistics and organization are thanked for their efforts. Labview software for operating the Fe(II) FIA system was designed by

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“…A 3 rd outdoor mesocosm experiment (Taliarte, Gran Canaria, March 2016) used 8 cylindrical polyurethane bags with a depth of approximately 3 m, a starting volume of ~8000 L and no lid or screen on top (for further details see Filella et al, 2018 andHopwood et al, 2018a). After filling with coastal seawater the bags were allowed to stand for 4 days.…”

Section: Mesocosm Set Up and Samplingmentioning

confidence: 99%

Fe(II) stability in seawater

Hopwood

Santana-González

Gallego-Urrea

et al. 2018

Preprint

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Abstract. The speciation of dissolved iron (DFe) in the ocean is widely assumed to consist exclusively of Fe(III)-ligand complexes. Yet in most aqueous environments a poorly defined fraction of DFe also exists as Fe(II). Here we deploy flow injection analysis to measure in-situ Fe(II) concentrations during a series of mesocosm/microcosm experiments in coastal environments in addition to the decay rate of this Fe(II) when moved into the dark. During 5 mesocosm/microcosm experiments in Svalbard and Patagonia, where dissolved (0.2&#8201;&#181;m) Fe and Fe(II) were quantified simultaneously, Fe(II) constituted 24&#8211;65&#8201;% of DFe suggesting that Fe(II) was a large fraction of the DFe pool. When this Fe(II) was allowed to decay in the dark, the vast majority of measured oxidation rate constants were retarded relative to calculated constants derived from ambient temperature, salinity, pH and dissolved O2. The oxidation rates of Fe(II) spikes added to Atlantic seawater more closely matched calculated rate constants. The difference between observed and theoretical decay rates in Svalbard and Patagonia was most pronounced at Fe(II) concentrations <&#8201;2&#8201;nM and attributed to a stabilising effect of cellular exudates upon Fe(II). This enhanced stability of Fe(II) under post-bloom conditions, and the existence of such a high fraction of DFe as Fe(II), challenges the assumption that DFe speciation is dominated by ligand bound-Fe(III) species.

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Photochemical vs. Bacterial Control of H2O2 Concentration Across a pCO2 Gradient Mesocosm Experiment in the Subtropical North Atlantic

Cited by 5 publications

References 51 publications

Plankton Community Respiration and ETS Activity Under Variable CO2 and Nutrient Fertilization During a Mesocosm Study in the Subtropical North Atlantic

Plankton Community Respiration and ETS Activity Under Variable CO2 and Nutrient Fertilization During a Mesocosm Study in the Subtropical North Atlantic

Fe(II) stability in coastal seawater during experiments in Patagonia, Svalbard, and Gran Canaria

Fe(II) stability in seawater

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