Posts Tagged 'methods'



Ocean acidification and marine microorganisms: responses and consequences

Ocean acidification (OA) is one of the global issues caused by rising atmospheric CO2. The rising pCO2 and resulting pH decrease has altered ocean carbonate chemistry. Microbes are key components of marine environments involved in nutrient cycles and carbon flow in marine ecosystems. However, these marine microbes and the microbial processes are sensitive to ocean pH shift. Thus, OA affects the microbial diversity, primary productivity and trace gases emission in oceans. Apart from that, it can also manipulate the microbial activities such as quorum sensing, extracellular enzyme activity and nitrogen cycling. Short-term laboratory experiments, mesocosm studies and changing marine diversity scenarios have illustrated undesirable effects of OA on marine microorganisms and ecosystems. However, from the microbial perspective, the current understanding on effect of OA is based mainly on limited experimental studies. It is challenging to predict response of marine microbes based on such experiments for this complex process. To study the response of marine microbes towards OA, multiple approaches should be implemented by using functional genomics, new generation microscopy, small-scale interaction among organisms and/or between organic matter and organisms. This review focuses on the response of marine microorganisms to OA and the experimental approaches to investigate the effect of changing ocean carbonate chemistry on microbial mediated processes.

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Coralline red algae: a proxy in climate and ocean acidification studies

Coralline red algae (Corallinaceae, Rhodophyta) play a major role in the ecology and structure of photic hard bottoms as well as many soft bottoms throughout the world oceans. As major calcifying organisms widely distributed in shallow marine systems and with an extensive fossil record, they can be used as an ideal proxy in environmental and (paleo)climate studies. This paper aims to be a short overview of the major characteristics of corallines as major important carbonate producers in shallow coastal marine areas worldwide and its value as a proxy in climate and ocean acidification research.

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Ocean acidification has different effects on the production of DMS and DMSP measured in cultures of Emiliania huxleyi and a mesocosm study: a comparison of laboratory monocultures and community interactions

The human-induced rise in atmospheric carbon dioxide since the industrial revolution has led to increasing oceanic carbon uptake and changes in seawater carbonate chemistry, resulting in lowering of surface water pH. In this study we investigated the effect of increasing pCO2 on concentrations of volatile biogenic dimethylsulphide (DMS) and its precursor dimethylsulphoniopropionate (DMSP), through monoculture studies and community pCO2 perturbation. DMS is a climatically important gas produced by many marine algae: it transfers sulphur into the atmosphere and is a major influence on biogeochemical climate regulation through breakdown to sulphate and formation of subsequent cloud condensation nuclei (CCN). Overall, production of DMS and DMSP by the coccolithophore Emiliania huxleyi strain RCC1229 was unaffected by growth at 900 µatm pCO2, but DMSP production normalised to cell volume was 12% lower at the higher pCO2 treatment. These cultures were compared with community DMS and DMSP production during an elevated pCO2 mesocosm experiment with the aim of studying E. huxleyi in the natural environment. Results contrasted with the culture experiments and showed reductions in community DMS and DMSP concentrations of up to 60% and 32% respectively at pCO2 up to 3000 µatm, with changes attributed to poorer growth of DMSP-producing nanophytoplankton species, including E. huxleyi, and potentially increased microbial consumption of DMS and dissolved DMSP at higher pCO2. DMS and DMSP production differences between culture and community likely arise from pH affecting the inter-species responses between microbial producers and consumers.

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LA-ICP-MS-derived U-concentrations and microstructural domains within biogenic aragonite of Arctica islandica shell

Understanding of the uranium uptake processes (both in vivo and post-mortem) into the skeletal structures of marine calcifiers is a subject of multi-disciplinary interest. U-concentration changes within the molluscan shell may serve as a paleoceanographic proxy of the pH history. A proxy of this type is needed to track the effects of fossil fuel emissions to ocean acidification. Moreover, attaining reliable U-series dates using shell materials would be a geochronological breakthrough. Picturing the high-resolution changes of U-concentrations in shell profiles is now possible by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). Here, we analyzed in situ U-concentration variations in sub-fossilized shells of ocean quahog (Arctica islandica), a commonly studied bivalve species in Quaternary geoscience, using LA-ICP-MS. Microstructural details of the shell profiles were achieved by the scanning electron microscopy (SEM). Comparison of the shell aragonite microstructure with the changes in U-concentration revealed that uranium of possibly secondary origin is concentrated into the porous granular layers of the shell. Our results reinforce the hypothesis that U-concentration variations can be linked with microstructural differences within the shell. A combination of LA-ICP-MS and SEM analyses is recommended as an interesting approach for understanding the U-concentration variations in similar materials.

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Shallow CO2 seeps for ocean acidification research: Geochemistry of two sites in Shikine Island and potential of the research in Japan

Shallow CO2 seeps, where CO2 gas is venting underwater, offer great potential for studies into the effects of ocean acidification at the ecosystem level. To our knowledge, only two tropical system and two temperate systems of such seeps have been described worldwide. Here we describe two new temperate systems: the Mikama Bay and Ashitsuke sites, located on Shikine Island, Japan. The Mikama Bay site is located in a shallow bay. Investigation of the gas and water chemistry showed that the gas contained 98% CO2 and up to 90 ppm H2S. Total alkalinity was constant in time and space with an average of 2265±10 μ mol kg−1. Mapping of Eh and pH showed that the low pH zones were the largest when currents were moderate. Under moderate currents, Eh values were globally higher and total sulfides concentration lower, supporting that a longer residence time of the bay water allow the oxidation of the sulfides to sulfates. Zones suitable for acidification studies: with a pH lower than 8.0, low saturation state of calcite and aragonite, and non-detectable sulfide concentration, can be defined a few meters from the main venting zone. The second site, Ashitsuke, is located in the inter-tidal zone on a shore composed of boulders. Several areas showed reduced pH sometimes restricted to a few meters and up to 20 m long along the shoreline. Temperature was higher in some of the reduced pH zones suggesting the presence of hot springs in addition to vents. This paper also highlights the need for discovering additional CO2 seeps, which by their nature often lack comparable replicates and can be confounded by factors other than CO2. In this regard, Japan offers great potential as it is home to numerous active volcanoes, representing potential venting sites in climates ranging from tropical to sub-polar.

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Experimental design in ocean acidification research: problems and solutions

Ocean acidification has been identified as a risk to marine ecosystems, and substantial scientific effort has been expended on investigating its effects, mostly in laboratory manipulation experiments. However, performing these manipulations correctly can be logistically difficult, and correctly designing experiments is complex, in part because of the rigorous requirements for manipulating and monitoring seawater carbonate chemistry. To assess the use of appropriate experimental design in ocean acidification research, 465 studies published between 1993 and 2014 were surveyed, focusing on the methods used to replicate experimental units. The proportion of studies that had interdependent or non-randomly interspersed treatment replicates, or did not report sufficient methodological details was 95%. Furthermore, 21% of studies did not provide any details of experimental design, 17% of studies otherwise segregated all the replicates for one treatment in one space, 15% of studies replicated CO2 treatments in a way that made replicates more interdependent within treatments than between treatments, and 13% of studies did not report if replicates of all treatments were randomly interspersed. As a consequence, the number of experimental units used per treatment in studies was low (mean = 2.0). In a comparable analysis, there was a significant decrease in the number of published studies that employed inappropriate chemical methods of manipulating seawater (i.e. acid–base only additions) from 21 to 3%, following the release of the “Guide to best practices for ocean acidification research and data reporting” in 2010; however, no such increase in the use of appropriate replication and experimental design was observed after 2010. We provide guidelines on how to design ocean acidification laboratory experiments that incorporate the rigorous requirements for monitoring and measuring carbonate chemistry with a level of replication that increases the chances of accurate detection of biological responses to ocean acidification.

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Proxy development and application for reconstructing the surface ocean carbonate system

Over the last two centuries, human activities have led to an unprecedented rate of carbon input into the atmosphere and oceans resulting in an alarmingly rapid decline in surface ocean pH, a process referred to as ocean acidification (OA). This process is leading to an observed decline in the carbonate ion concentrations ([CO32-]) in seawater – an ion that a large number of marine organisms (e.g. corals, foraminifera) utilize to secrete their skeletons and shells. The ability to identify past ocean acidification events using the marine sedimentary record can shed light on future impacts of the modern OA dilemma. Planktonic foraminifera have the ability to record the physical and chemical properties of the seawater in which they calcified, therefore the fossil shells of foraminifera serve as archives for past climatic and oceanographic conditions. Here, we present a new proxy surface ocean [CO32-] – planktonic foraminferal area density – and establish methods for a known proxy for surface ocean pH – the boron isotopic composition of foraminiferal calcite (δ11B). These proxies are used to reconstruct changes in the surface ocean carbonate system of the eastern equatorial Pacific over the last 35, 000 years using marine sediment core TR163-19 collected from the Cocos Ridge (2°16’N, 90°57’W, 2,348 m). The stable carbon and oxygen isotopic compositions of two morphotypes of planktonic foraminifer Orbulina universa collected from the Cariaco Basin, Venezuela are also investigated, with results suggesting that the two morphotypes record different environmental signals in the calcite shells and should not be used together during paleoceanographic reconstructions.

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How can present and future satellite missions support scientific studies that address ocean acidification?

Space-based observations offer unique capabilities for studying spatial and temporal dynamics of the upper ocean inorganic carbon cycle and, in turn, supporting research tied to ocean acidification (OA). Satellite sensors measuring sea surface temperature, color, salinity, wind, waves, currents, and sea level enable a fuller understanding of a range of physical, chemical, and biological phenomena that drive regional OA dynamics as well as the potentially varied impacts of carbon cycle change on a broad range of ecosystems. Here, we update and expand on previous work that addresses the benefits of space-based assets for OA and carbonate system studies. Carbonate chemistry and the key processes controlling surface ocean OA variability are reviewed. Synthesis of present satellite data streams and their utility in this arena are discussed, as are opportunities on the horizon for using new satellite sensors with increased spectral, temporal, and/or spatial resolution. We outline applications that include the ability to track the biochemically dynamic nature of water masses, to map coral reefs at higher resolution, to discern functional phytoplankton groups and their relationships to acid perturbations, and to track processes that contribute to acid variation near the land-ocean interface.

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Technology for ocean acidification research: needs and availability

Diverse instruments, both custom built and commercially available, have been used to measure the properties of the aqueous CO2 system in seawater at differing levels of autonomy (automated benchtop, continuous underway, autonomous in situ). In this review, we compare the capabilities of commercially available instruments with the needs of oceanographers in order to highlight major shortfalls in the state-of-the art instrumentation broadly available to the ocean acidification (OA) scientific community. In addition, we describe community surveys that identify needs for continued development and refinement of sensor and instrument technologies, expansion of programs that provide Certified Reference Materials, development of best practices documentation for autonomous sensors, and continued and expanded sensor intercomparison experiments.

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A metadata template for ocean acidification data

This paper defines the best practices for documenting ocean acidification (OA) data and presents a framework for an OA metadata template. Metadata is structured information that describes and locates an information resource. It is the key to ensuring that a data set will be accessible into the future. With the rapid expansion of studies on biological responses to OA, the lack of a common metadata template to document the resulting data poses a significant hindrance to effective OA data management efforts. In this paper, we present a metadata template that can be applied to a broad spectrum of OA studies, including those studying the biological responses to OA. The “variable metadata section”, which includes the variable name, observation type, whether the variable is a manipulation condition or response variable, and the biological subject on which the variable is studied, forms the core of this metadata template. Additional metadata elements, such as investigators, temporal and spatial coverage, and data citation, are essential components to complete the template. We explain the structure of the template, and define many metadata elements that may be unfamiliar to researchers.

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Oxygen metabolism and pH in coastal ecosystems: Eddy Covariance Hydrogen ion and Oxygen Exchange System (ECHOES)

An aquatic eddy covariance (EC) system was developed to measure the exchange of oxygen (O2) and hydrogen ions (H+) across the sediment-water interface. The system uses O2 optodes and a newly developed micro-flow cell H+ ion selective field effect transistor; these sensors displayed sufficient precision and rapid enough response times to measure concentration changes associated with turbulent exchange. Discrete samples of total alkalinity and dissolved inorganic carbon were used to determine the background carbonate chemistry of the water column and relate the O2 and H+ fluxes to benthic processes. The ECHOES system was deployed in a eutrophic estuary (Waquoit Bay), and revealed that the benthos was a sink for acidity during the day and a source of acidity during the night, with H+ and O2 fluxes of ± 0.0001 and ± 10 mmol m−2 h−1, respectively. H+ and O2 fluxes were also determined using benthic flux chambers, for comparison with the EC rates. Chamber fluxes determined in 0.25 h intervals co-varied with EC fluxes but were ∼ 4 times lower in magnitude. This difference was likely due to suppressed pore-water advection in the chambers and changes in the chemistry of the enclosed chamber overlying water. The individual H+ and O2 fluxes were highly correlated in each dataset (EC and chambers), and both methods yielded H+ fluxes that could not be explained by O2 metabolism alone. The ECHOES system provides a new tool for determining the influence of benthic biogeochemical cycling on coastal ocean acidification and carbon cycling.

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Best Practices for autonomous measurement of seawater pH with the Honeywell Durafet pH sensor

The California Current Acidification Network (C-CAN) is a collaboration dedicated to advancing understanding of ocean acidification (OA) and its effects on biological resources of the U.S. West Coast. C-CAN first convened in 2010 in response to a growing realization that declines in shellfish hatchery production corresponded to coastal upwelling of low pH waters. The initial workshop brought together leading shellfish industry representatives, coastal managers, researchers, Sea Grant programs, and Integrated Ocean Observing Systems to increase collective understanding of OA effects on the nearshore environment. C-CAN has since expanded to include other ocean-dependent industries, environmental advocacy groups, regulatory agencies, and tribal groups.

The overarching goal of C-CAN is to coordinate and standardize OA measurement and data collection practices, ensuring data accessibility, utility, and application. C-CAN provides shared guidelines and support for participating groups in implementation of high quality, compatible monitoring programs. C-CAN also facilitates application of the network’s data in developing tools that examine the causes of ecosystem impacts and predict future changes in ocean chemistry and biological communities. Finally, C-CAN communicates its findings to address management concerns about defining the ecological effects of OA for development of mitigation and adaptation strategies. Given the complexity of this emerging issue, and recognizing that advancing knowledge will require a concerted community effort, C-CAN is committed to serve as the region’s source of reliable, vetted scientific information on ocean acidification.

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The coordination and distribution of B in foraminiferal calcite

The isotopic ratio and concentration of B in foraminiferal calcite appear to reflect the pH and bicarbonate concentration of seawater. The use of B as a chemical proxy tracer has the potential to transform our understanding of the global carbon cycle, and ocean acidification processes. However, discrepancies between the theory underpinning the B proxies, and mineralogical observations of B coordination in biomineral carbonates call the basis of these proxies into question. Here, we use synchrotron X-ray spectromicroscopy to show that B is hosted solely as trigonal BO3 in the calcite test of Amphistegina lessonii, and that B concentration exhibits banding at the micron length scale. In contrast to previous results, our observation of trigonal B agrees with the predictions of the theoretical mechanism behind B palaeoproxies. These data strengthen the use of B for producing palaeo-pH records. The observation of systematic B heterogeneity, however, highlights the complexity of foraminiferal biomineralisation, implying that B incorporation is modulated by biological or crystal growth processes.

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Impact of CO2-driven acidification on the development of the sea cucumber Apostichopus japonicus (Selenka) (Echinodermata: Holothuroidea)

We evaluated the impact of ocean acidification on the early development of sea cucumber Apostichopus japonicus. The effect of pH-levels (pH 8.04, 7.85, 7.70 and 7.42) were tested on post-fertilization success, developmental (stage duration) and growth rates. Post-fertilization success decreased linearly with pH leading to a 6% decrease at pH 7.42 as compared to pH 8.1. The impact of pH on developmental time was stage-dependent: (1) stage duration increased linearly with decreasing pH in early-auricularia stage; (2) decreased linearly with decreasing pH in the mid-auricularia stage; but (3) pH decline had no effect on the late-auricularia stage. At the end of the experiment, the size of doliolaria larvae linearly increased with decreasing pH. In conclusion, a 0.62 unit decrease in pH had relatively small effects on A. japonicus early life-history compared to other echinoderms, leading to a maximum of 6% decrease in post-fertilization success and subtle effects on growth and development.

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Corrigendum to “Boron incorporation in the foraminifer Amphistegina lessonii under a decoupled carbonate chemistry” published in Biogeosciences, 12, 1753–1763, 2015

The authors regret that a typographical error appeared in the above paper on page 1756, first column, lines 8–9. The authors apologise for any inconvenience caused, and the correct lines should read as follows: Our estimate of δ11Bsw of 39.8 ± 0.4 ‰ (2 SD, n = 30) is independent of sample size and is in agreement with published values of 39.6 ± 0.2 ‰ (2 SD) (Foster et al., 2010) and 39.7 ± 0.6 ‰ (2 SD) (Spivack and Edmond, 1987).

Continue reading ‘Corrigendum to “Boron incorporation in the foraminifer Amphistegina lessonii under a decoupled carbonate chemistry” published in Biogeosciences, 12, 1753–1763, 2015’

Optimising methodology for determining the effect of ocean acidification on bacterial extracellular enzymes

To fully understand the impact of ocean acidification on biogeochemical cycles, the response of bacterial extracellular enzymes needs to be considered as they play a central role in the degradation and distribution of labile organic matter. This study investigates the methodology, and potential artefacts involved in determining the response of bacterial extracellular glucosidase and protease to ocean acidification. The effect of pH on artificial fluorophores and substrates was examined, as well as the impact of three different acidification methods. The results indicate that pH has a significant effect on the fluorescence of the artificial fluorophore 4-methylumbeliferone for glucosidase activity, and 7-amino-4-methylcoumarin for protease activity, while artificial aminopeptidase substrate alters the pH of seawater, confirming previous observations. Before use in ocean acidification research these enzyme assay components must be buffered in order to stabilise sample pH. Reduction of coastal seawater pH to 7.8 was shown to increase β-glucosidase activity rapidly (0.5 h), while no significant response was detected for leucine aminopeptidase, highlighting the need for short-term direct effects of pH on enzyme activities. Bubbling with CO2 gas resulted in higher β-glucosidase activity when compared to acidification using gas-permeable silicon tubing and acidification with HCl. Although bubbling showed variable effects between two experiments conducted at different times of the year. In addition, bacterial cell numbers were 15–40% higher with bubbling relative to seawater acidified with gas-permeable silicon tubing and HCl. Artefacts associated with bubbling may lead to the overestimation of extracellular enzyme activities, and interpretation of the impacts of ocean acidification on organic matter cycling.

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Effect of climate change on crustose coralline algae at a temperate vent site, White Island, New Zealand

Natural CO2 vents allow study of the effects of climate change on marine organisms on a different scale from laboratory-based studies. This study outlines a preliminary investigation into the suitability of natural CO2 vents near White Island, Bay of Plenty, New Zealand (37°31.19′S, 117°10.85′E) for climate change research by characterising water chemistry from two vent and three control locations on a seasonal basis, as well as examining their effects on skeletons of the local calcifying crustose coralline algae. pH measurements at vent sites, calculated from dissolved inorganic carbon and alkalinity, showed reduced mean pH levels (7.49 and 7.85) relative to background levels of 8.06, whereas mean temperatures were between 0.0 and 0.4°C above control. Increases in sulfur and mercury at sites near White Island were probably a result of volcanic unrest. Crustose coralline algae did not show significant variability in skeletal Mg-calcite geochemistry, but qualitative comparisons of calcite skeletons under scanning electron microscopy saw greater deformation and dissolution in coralline algae calcite crystals from vent sites compared to controls. Although additional monitoring of pH fluctuations and hydrogen sulphides is still needed, the low pH and increased temperatures indicate potential for studying multistressor effects of projected climate changes in a natural environment.

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New carbonate system proxies: foram culturing and pteropod potentials

Global climate change is one of the most pressing challenges our society is facing currently. Climate sensitivity due to atmospheric CO2 doubling will most likely increase global temperatures by 2.0 – 4.5 °C (IPCC 2007). While some direct effects of increasing CO2 are straightforward (e.g. ocean acidification, atmospheric temperature rise), the mid- and long-term impacts of increasing CO2 levels are less easily predicted due to poorly qualified contribution from various potential positive and negative feedbacks in the climate system. Palaeoreconstructions combining temperature reconstructions and atmospheric paleo-CO2 levels are necessary to validate models that aim at predicting future global temperature increases. Reconstructions of atmospheric CO2 from ice-cores are confined to the last 800 ka (Lüthi et al. 2008), while reconstruction of atmospheric pCO2 on longer timescales rely largely on marine sedimentary archives (e.g. Hönisch et al. 2012). Within the latter, foraminifera play a central role, since the chemical and isotopic composition of their shells reflect the physicochemical properties of the seawater that these organisms grew in (Emiliani 1955). Palaeo atmospheric CO2 concentrations can be estimated from past seawater CO2 (aq), which in turn can be reconstructed when two out of six parameters are known of the oceans carbonate system (“C-system”; CO2,HCO3–, CO32–, pH, DIC [dissolved inorganic carbon] and total alkalinity). (…)

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Carbonate chemistry co-variation with temperature and oxygen in coastal environments and the design of ecologically relevant ocean acidification experiments

Ocean acidification (OA) is expected to have major impacts on marine ecosystems by directly influencing organismal performance (e.g., growth, development, survival) and indirectly through shifts in food web structure or competitive interactions. Our ability to predict the effects of OA on most species is currently limited but growing, and CO2 exposure experiments are central to efforts to increase understanding.

Typically, experiments include control conditions that attempt to simulate contemporary or preindustrial seawater CO2 concentrations and acidified treatments that correspond to potential future CO2 uptake by the oceans. For studies focused on organisms from low productivity, open-ocean surface waters, researchers can rely on IPCC simulations of future atmospheric CO2 partial pressure (pCO2) to identify potential carbonate chemistry treatments because assumptions of air-sea pCO2 equilibrium are often nearly met (1). In contrast, pCO2 can be far from air-sea equilibrium in many coastal systems, and considerable spatial and temporal variation can exist due to multiple processes, including high rates of primary production and respiration, freshwater inputs, and upwelling (2, 3). To estimate the potential impact of OA on organisms from these regions, control pCO2 levels that reflect contemporary ambient conditions are needed. Recognition of this issue has led researchers to use data from coastal seawater chemistry monitoring programs to inform treatment levels in several recent OA experiments. (…)

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Boron incorporation in the foraminifer Amphistegina lessonii under a decoupled carbonate chemistry (update)

A number of studies have shown that the boron isotopic composition (δ11B) and the B / Ca ratio of biogenic carbonates (mostly foraminifers) can serve as proxies for two parameters of the ocean’s carbonate chemistry, rendering it possible to calculate the entire carbonate system. However, the B incorporation mechanism into marine carbonates is still not fully understood and analyses of field samples show species-specific and hydrographic effects on the B proxies complicating their application. Identifying the carbonate system parameter influencing boron incorporation is difficult due to the co-variation of pH, CO32- and B(OH)4-. To shed light on the question which parameter of the carbonate system is related to the boron incorporation, we performed culture experiments with the benthic symbiont-bearing foraminifer Amphistegina lessonii using a decoupled pH–CO32- chemistry. The determination of the δ11B and B / Ca ratios was performed simultaneously by means of a new in situ technique combining optical emission spectroscopy and laser ablation MC-ICP-MS. The boron isotopic composition in the tests gets heavier with increasing pH and B / Ca increases with increasing B(OH)4- / HCO3- of the culture media. The latter indicates that boron uptake of A. lessonii features a competition between B(OH)4- and HCO3-. Furthermore, the simultaneous determination of B / Ca and δ11B on single specimens allows for assessing the relative variability of these parameters. Among different treatments the B / Ca shows an increasing variability with increasing boron concentration in the test whereas the variability in the isotope distribution is constant.

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