Posts Tagged 'methods'

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Characterization of the nonlinear salinity dependence of glass pH electrodes: A simplified spectrophotometric calibration procedure for potentiometric seawater pH measurements at 25 °C in marine and brackish waters: 0.5 ≤ S ≤ 36

Published 3 February 2020 Science Closed
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Highlights

• Calibration parameters for glass pH electrodes are highly nonlinear at salinities <5.

• These nonlinearities can lead to pH measurement errors of 0.12 to 0.24 at S < 5.

• A method is presented to calibrate pH electrodes over a river-to-sea range of S.

• Such calibrations require <3 h.

• These calibrations allow for quantitative electrode pH measurements over 0.5 < S < 36.1.

Abstract

Glass electrodes are commonly used to measure the pH of natural waters over various, sometimes wide, ranges of salinity (S). For such applications, the electrodes must be calibrated against solutions of known pH and salinity identical to those of the sample solutions. Well-characterized buffer solutions may be used for these calibrations, but if a wide range of salinity is to be encountered in the samples (e.g., as in estuarine transects), this approach is quite laborious. Previous work has demonstrated that for 28.5 < S < 36.1, pH electrodes can be efficiently calibrated spectrophotometrically in seawater because electrode intercept potential E0 (a key calibration parameter) varies linearly with salinity over that range. The present work (a) characterizes pH electrode calibration parameters in seawater over a wider range of salinity (0.5 < S < 36) and (b) provides a simple and efficient method for creating and maintaining “river-to-sea” electrode calibrations over periods of months. Electrode calibration slope (g’) was found to be insensitive to salinity, as expected. The value of this parameter, measured at S > 5, was reliably consistent with theoretical expectations, such that repeat verification needs to be conducted only occasionally. Electrode intercept potential (E0), in contrast, was found to depend substantially on salinity: approximately linearly for 5 ≤ S ≤ 36 and substantially nonlinearly for 0.5 ≤ S < 5. Ignoring this dependence of E0 on S can lead to pH misestimates as large as 0.24, with the problem being most severe at lower salinities. Based on these observations, a method was developed by which the dependence of E0 on S can be rapidly ascertained by simultaneously measuring pH (spectrophotometrically) and electromotive force (potentiometrically) in seawater that is serially diluted to produce the full range of salinities to be encountered in sampling. Because no acid titrations are required, a full river-to-sea calibration can be acquired in <3 h. With occasional (daily to weekly) one-point checks/corrections for electrode drift, this calibration is stable for weeks to months.

Continue reading ‘Characterization of the nonlinear salinity dependence of glass pH electrodes: A simplified spectrophotometric calibration procedure for potentiometric seawater pH measurements at 25 °C in marine and brackish waters: 0.5 ≤ S ≤ 36’

pH electrodes based on iridium oxide films for marine monitoring

Published 3 February 2020 Science Closed
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Highlight

• The preparation method of the IROFs pH electrode is systematically introduced.

• The IROFs pH electrode methods are compared with the traditional pH value analysis and monitoring methods in the marine environment.

• Innovative trend of pH analysis and monitoring is expanded in marine organization, seawater and sediment pore water.

Abstract

The pH is an important parameter that affects the growth and development of marine organisms, environmental changes, and industrial and agricultural production processes. Nowadays, important trends in pH detection and analysis are higher stability, adaptation to extreme environmental conditions, miniaturization, portability, and digital intelligence. Several studies have focused on the application of the iridium oxide film (IROF) pH electrodes in water quality monitoring and physiological analysis. The central aim of this work was to review the preparation techniques of the IROF pH electrodes and to expand their application in the field of marine monitoring. The studied methods include electrochemical deposition, electrochemical growth, sputtering deposition, heat treatment, and novel preparation methods. The IROF pH electrodes prepared via these methods are more sensitive, have a wider pH measurement ranges, and can be miniaturized further than traditional glass and pH photometer. Hence, in environmental analysis, combining IROF pH electrodes with wireless technology for the physiological and biochemical analysis of marine organisms, seawater, and sediment pore water is an important development tendency.

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Measurement of feeding rates, respiration, and pH regulatory processes in the light of ocean acidification research

Published 31 January 2020 Science Closed
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The physiology of marine larvae has received considerable attention in the context of anthropogenic ocean acidification (OA). Many marine larvae including those of echinoderms, hemichordates, and mollusks are characterized by a developmental delay when exposed to reductions in seawater pH with the underlying mechanisms being largely unexplored.

A key task in the frame of OA research lies in the identification of unifying physiological principles that may explain reductions in growth and development. The sea urchin larva has been identified as a good model organism, and energy allocations toward compensatory processes were found to be key factors affecting development. However, physiological approaches to assess the animal’s energy budget, as well as methods to characterize energy consuming processes (e.g., gut pH homeostasis and biomineralization) were scarce. During the last decade, a suite of physiological techniques was developed, to accurately determine the larval energy budget including feeding and metabolic rate measurements. To identify and characterize energy consuming processes, gastroscopic pH measurements in the larval gut and intracellular pH measurements of primary mesenchyme cells were developed.

These techniques helped to understand fundamental processes of gut homeostasis and biomineralization in the developing sea urchin larva and their interaction with the environment. Using the sea urchin larva as a model these methods were successfully transferred to other echinoderm and hemichordate early developmental stages. This chapter explains and provides the methodological basis for the determination of feeding and metabolic rates as well as intracellular and extracellular pH measurements using the sea urchin larva as an example.

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Equipping smart coasts with marine water quality IoT sensors

Published 24 January 2020 Science Closed
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Highlights

• This micro-manuscript describes a university/industry collaboration to study water quality at a shellfish hatchery.

• We designed a real-time communications system including hardware, firmware, and web visualization/analysis software.

• A dashboard is located at sccoos.org/ocean-acidification/ and code at github.com/SUPScientist/Equipping-Smart-Coasts.

Abstract

Ocean acidification, the decrease in seawater pH as a result of increasing carbon dioxide, has been shown to be an important driver of oyster mortality in West Coast shellfisheries [1]. Yet carbon chemistry is only sparsely measured, especially relative to its high variability in coastal ecosystems, due to the complexity and cost of appropriate sensors and their maintenance. Worse, data are rarely communicated in real time to water quality or aquacultural managers. In the Agua Hedionda Lagoon (AHL) in Carlsbad, CA, researchers from Scripps Institution of Oceanography and industry representatives from the Carlsbad Aquafarm have come together through a NOAA-facilitated project to alleviate this data shortage using a combination of cutting-edge research technology alongside off-the-shelf and easy-to-implement IoT communications packages.

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Use of high-frequency noninvasive electromagnetic biosensors to detect ocean acidification effects on shellfish behavior

Published 17 January 2020 Science Closed
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Although ocean acidification studies related to marine animal behavior have increased in recent years, the behavioral effects of ocean acidification on shellfish are relatively understudied, even though marine shellfish exhibit a wealth of behaviors that can modify organismal interactions and biological community functioning. Furthermore, detecting acute behavioral changes may provide a biological indicator of ecosystem stress and/or an early warning system for aquaculture operations. This article highlights a new and emerging technology—high-frequency noninvasive (HFNI) electromagnetic biosensors—that can be used to document acute and long-term effects of elevated CO2 on the valve-gaping behavior of marine bivalves. An overview of the technology is presented, and the current and potential uses of these biosensors in ocean acidification research are highlighted, along with current limitations and next steps. Although a handful of studies have used these biosensors to test for effects of acidification on bivalve valve-gaping behavior, their potential for testing critical and novel hypotheses regarding ocean acidification effects in a broader range of shellfish taxa is currently underused. Ultimately, this article provides a basis for expanding ocean acidification research on shellfish behavior through the use of HFNI electromagnetic biosensors.

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Coral reef pH altered in situ

Published 16 January 2020 Media coverage , Science Closed
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A Free Ocean Carbon Enrichment experiment that manipulates seawater pH on a coral reef flat shows that the level of ocean acidification at which net dissolution of corals occurs may arrive much sooner than expected.

Coral reefs are at the forefront of public perception about the impacts of climate change in the world’s oceans. Along with warming, which induces coral bleaching and mortality, the decreasing pH of seawater due to ocean acidification is expected to have dire consequences for coral reefs as we know them, in part through lower availability of carbonate ions (CO32–), which are used in combination with calcium ions (Ca2+) by corals for skeletal growth. Writing in Nature Ecology & Evolution, Kline et al. report their use of Free Ocean Carbon Enrichment (FOCE) technology to investigate coral calcification and dissolution in an in situ ocean acidification experiment on a coral reef flat on the Great Barrier Reef, over a period of 200 d. Although their study is of a single coral species in a single location, the realistic setting makes this study particularly relevant.

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The development and validation of a profiling glider deep ISFET-based pH sensor for high resolution observations of coastal and ocean acidification

Published 30 October 2019 Science Closed
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Coastal and ocean acidification can alter ocean biogeochemistry, with ecological consequences that may result in economic and cultural losses. Yet few time series and high resolution spatial and temporal measurements exist to track the existence and movement of water low in pH and/or carbonate saturation. Past acidification monitoring efforts have either low spatial resolution (mooring) or high cost and low temporal and spatial resolution (research cruises). We developed the first integrated glider platform and sensor system for sampling pH throughout the water column of the coastal ocean. A deep ISFET (Ion Sensitive Field Effect Transistor)-based pH sensor system was modified and integrated into a Slocum glider, tank tested in natural seawater to determine sensor conditioning time under different scenarios, and validated in situ during deployments in the U.S. Northeast Shelf (NES). Comparative results between glider pH and pH measured spectrophotometrically from discrete seawater samples indicate that the glider pH sensor is capable of accuracy of 0.011 pH units or better for several weeks throughout the water column in the coastal ocean, with a precision of 0.005 pH units or better. Furthermore, simultaneous measurements from multiple sensors on the same glider enabled salinity-based estimates of total alkalinity (AT) and aragonite saturation state (ΩArag). During the Spring 2018 Mid-Atlantic deployment, glider pH and derived AT/ΩArag data along the cross-shelf transect revealed higher pH and ΩArag associated with the depth of chlorophyll and oxygen maxima and a warmer, saltier water mass. Lowest pH and ΩArag occurred in bottom waters of the middle shelf and slope, and nearshore following a period of heavy precipitation. Biofouling was revealed to be the primary limitation of this sensor during a summer deployment, whereby offsets in pH and AT increased dramatically. Advances in anti-fouling coatings and the ability to routinely clean and swap out sensors can address this challenge. The data presented here demonstrate the ability for gliders to routinely provide high resolution water column data on regional scales that can be applied to acidification monitoring efforts in other coastal regions.

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A photonic pH sensor based on photothermal spectroscopy

Published 24 October 2019 Science Closed
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Although the determination of pH is a standard laboratory measurement, new techniques capable of measuring pH are being developed to facilitate modern technological advances. Bio-industrial processing, tissue engineering, and intracellular environments impose unique measurement requirements on probes of pH. We describe a fiber optic-based platform, which measures the heat released by chromophores upon absorption of light. The optical fibers feature fiber Bragg gratings (FBG) whose Bragg peak redshifts with increasing temperature. Using anthocyanins (pH-sensitive chromophores found in many plants), we are able to correlate visible light absorption by a solution of anthocyanins to heat released and changes in FBG signal over a pH range of 2.5–10. We tested the ability of this platform to act as a sensor coating the fiber within a layer of crosslinked polyethylene glycol diacrylate (PEG-DA). Incorporating the anthocyanins into the PEG, we find that the signal magnitude increases over the observed signal at the same pH in solution. Our results indicate that this platform is viable for assessing pH in biological samples and point at ways to optimize performance.

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Intercomparison of four methods to estimate coral calcification under various environmental conditions

Published 23 October 2019 Science Closed
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Coral reefs are constructed by calcifiers that precipitate calcium carbonate to build their shells or skeletons through the process of calcification. Accurately assessing coral calcification rates is crucial to determine the health of these ecosystems and their response to major environmental changes such as ocean warming and acidification. Several approaches have been used to assess rates of coral calcification but there is a real need to compare these approaches in order to ascertain that high quality and intercomparable results can be produced. Here, we assessed four methods (total alkalinity anomaly, calcium anomaly, 45Ca incorporation and 13C incorporation) to determine coral calcification of the reef-building coral Stylophora pistillata. Given the importance of environmental conditions on this process, the study was performed under two pH (ambient and low level) and two light (light and dark) conditions. Under all conditions, calcification rates estimated using the alkalinity and calcium anomaly techniques as well as 45Ca incorporation were highly correlated. Such a strong correlation between the alkalinity anomaly and 45Ca incorporation techniques has not been observed in previous studies and most probably results from improvements described in the present paper. The only method which provided calcification rates significantly different from the other three techniques was 13C incorporation. Calcification rates based on this method were consistently higher than those measured using the other techniques. Although reasons for these discrepancies remain unclear, the use of this technique for assessing calcification rates in corals is not recommended without further investigations.

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New methods for imaging and quantifying dissolution of pteropods to monitor the impacts of ocean acidification

Published 14 October 2019 Science Closed
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Large-scale changes in climate and ocean ecosystems demand innovative and cost-effective ways to track changes in the marine environment and its living resources. During the past decade, ocean acidification has become recognized as a major threat to the biodiversity of marine ecosystems during the 21st century. However, an important constraint on modern ocean acidification research is the lack of accessibility to effective imaging techniques, as well as accurate analytical methods. Here, we compare several different microscopic techniques to evaluate the relative merits of each. Additionally, a new dissolution quantification method is developed that more completely assesses damage over an entire shell. These findings can help expand the toolbox for scientists engaged in studying the impacts of ocean acidification on marine invertebrates and enable more researchers to participate in this vital field.

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Precision pH sensor based on WO3 nanofiber-polymer composites and differential amplification

Published 7 October 2019 Science Closed
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We report a new type of potentiometric pH sensor with sensitivity exceeding the theoretical Nernstian behavior (−59.1 mV/pH). For the pH-sensitive electrode, 1D tungsten oxide (WO3) nanofibers (NFs) were prepared to obtain large surface area and high porosity. These NFs were then stabilized in a reactive porous chloromethylated triptycene poly(ether sulfone) (Cl-TPES) binder, to facilitate proton diffusion into the polymer membrane. The measurements were performed with a differential amplifier using matched MOSFETs and providing a 10-fold amplified signal over a simple potentiometric determination. A high pH sensitivity of −377.5 mV/pH and a linearity of 0.9847 were achieved over the pH range of 6.90–8.94. Improved signal-to-noise ratios with large EMF signal changes of 175 mV were obtained in artificial seawater ranging pH 8.07–7.64 (ΔpH = 0.43), which demonstrates a practical application for pH monitoring in ocean environments.

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Automated alkalinity sensing system

Published 1 October 2019 Science Closed
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Ocean Acidification is a reduction in pH caused by the absorption of atmospheric CO2. Low pH decreases the availability of calcium carbonate to shell and skeleton secreting marine animals such as mollusks and corals reducing their growth rates and even causing death. Thus, monitoring oceanic conditions has become more and more important, in particular there is a need for extensive measurements of carbonate chemistry parameters over both space and time. This paper presents a low-cost, automated benchtop measuring system for total alkalinity, one of the important parameters for monitoring marine carbonate chemistry. This system addresses the need for a low-cost alkalinity sensing system that can be deployed in great numbers to provide the large data sets needed for to measure and predict the impact of ocean acidification on the marine ecosystem. It is based on a two-point acid titration method. Tests of the prototype have shown that the system gives acceptable results comparable to manual measurements. With hermetic repackaging, the system could be field deployed on platforms such as AUVs or buoys.

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Evaluating the planktic foraminiferal B/Ca proxy for application to deep time paleoceanography

Published 30 September 2019 Science Closed
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Highlights

  • Paleocene seawater chemistry affects planktic foraminifer boron/calcium proxy sensitivity.
  • T. sacculifer and O. universa shell boron content is similar to that of Paleogene species.
  • We present a new framework for applying B/Ca calibrations to the early Cenozoic.
  • Our new approach allows application of calibrations from modern species to extinct ones.

Abstract

The Cenozoic Era has been characterized by large perturbations to the oceanic carbon cycle and global climatic changes, but quantifying the magnitude and cause of these shifts is still subject to considerable uncertainty. The boron/calcium (B/Ca) ratio of fossil planktic foraminifera shells is a promising tool for reconstructing surface ocean carbonate chemistry during such events. Previous studies indicate that symbiont-bearing, planktic foraminiferal B/Ca depends on the [B(OH)4− /DIC] ratio of seawater and potentially, when combined with foraminiferal δ11 B proxy reconstructions of B(OH)4− , an opportunity to reconstruct surface ocean DIC in the geologic past. There are, however, two barriers towards interpreting records from the pre-Pleistocene era: (1) changes in seawater major ion chemistry in the past might have affected foraminiferal B/Ca; and (2) modern foraminifera species show variable B/Ca calibration sensitivities that cannot be constrained in now-extinct species. Here we address these challenges with new experiments in which we have cultured modern, symbiont-bearing foraminifera Globigerinoides ruber (pink) and Trilobatus sacculifer in seawater with simulated early Cenozoic seawater chemistry (high [Ca], low [Mg], and low [B]T). We explore mechanisms that can account for the inter-species trends that are observed in foraminiferal B/Ca, and propose a framework that can be used to apply B/Ca calibrations to now-extinct species for reconstructing climate perturbations under varying seawater chemistries.

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Present and future adaptation of marine species assemblages: DNA-based insights into climate change from studies of physiology, genomics, and evolution

Published 26 September 2019 Science Closed
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Marine species live in a dynamic physical and biological environment that demands frequent physiological adjustment and can result in strong natural selection or shifts in species ranges. We illustrate the patterns and processes of adaptation to environmental change with genetic-based examples that range from a focus on single proteins to whole genomes to whole communities. This work shows how single amino acid changes adapt proteins to function at different temperatures. It shows how acidification impacts expression of proteins in energy pathways in adults and exerts natural selection on many genes in larvae. Whole genome surveys along coastlines are now possible, and they reveal unexpected patterns of genetic differentiation even in highly dispersive species. Genetic surveys of over 70 species along the North American west coast show high levels of genetic diversity and genetic structure clustered at headlands and capes known to mark species range boundaries. Finally, new surveys of DNA variation in whole communities show promise for rapid monitoring that can augment and complement traditional dive surveys. Overall, dynamics in the physical environment have a strong effect on organism physiology, which results in diverse patterns of population growth and persistence, as well as of species range and evolutionary capacity. The high level of adaptive genetic variation shown here suggests an ability for marine populations to adapt in the face of climate change, but many questions remain about how fast, complete, and effective this evolution will be.

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Purification and characterization of thymol blue for spectrophotometric pH measurements in rivers, estuaries, and oceans

Published 17 September 2019 Science Closed
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Highlights

  • Thymol blue (TB) was purified using flash chromatography.
  • TB is useful for pH measurements above the range of meta-cresol purple (mCP).
  • Paired pH measurements directly link the equilibrium characteristics of TB and mCP.

Abstract

Thymol blue (TB) is one of a suite of indicator dyes appropriate for spectrophotometric determinations of the pH of aqueous solutions. For measurements of seawater pH, meta-cresol purple (mCP) is most often used, but TB is especially well suited for measurements in surface or shallow waters where the pH may exceed the optimal indicating range of mCP (e.g., due to photosynthesis). This work presents flash chromatography procedures for purifying commercially available TB and describes physical–chemical characteristics of the purified dye, thus enabling the acquisition of spectrophotometric pH measurements over a wide range of practical salinities (SP) and temperatures (T). The essential TB characteristics for 0 ≤ SP ≤ 40 and 278.15 ≤ T ≤ 308.15 K are described by:

pHT=−(log(K2Te2))+log((R−e1)/(1−Re4))TB

“>pHT=−(log(K2Te2))+log((R−e1)/(1−Re4))TB

(log(K2Te2))TB=6.6942-0.001129Sp0.5T-0.5926T-0.5Sp+619.40/T+0.1441SP-0.02591Sp1.5+0.0034Sp2-0.0001754Sp2.5

“>(log(K2Te2))TB=6.6942-0.001129Sp0.5T-0.5926T-0.5Sp+619.40/T+0.1441SP-0.02591Sp1.5+0.0034Sp2-0.0001754Sp2.5

e1 = −0.00132 + 0.00001600T

e4 = −0.005042 + 0.0002094T + 0.01916SP0.5/T

where pHT is pH determined on the total hydrogen ion concentration scale; R is the ratio of TB absorbances (A) at 435 and 596 nm (596A/435A); K2T is the equilibrium constant for the second TB dissociation step on the total scale; and e1, e2, and e4 are TB molar absorptivity ratios. This characterization was developed in a manner that ensures consistency with the primary TRIS buffer standards used in previously published characterizations of mCP. With this characterization, TB joins mCP as a sulfonephthalein indicator that has been characterized over the ranges of salinity and temperature required to make high-quality pH measurements in rivers, estuaries, and the open ocean. The full characterization of purified TB reported here extends the upper range of pHT that can be accessed with precise spectrophotometric measurements by approximately 0.50 pH units.

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Metered reagent injection into microfluidic continuous flow sampling for conductimetric ocean dissolved inorganic carbon sensing

Published 11 September 2019 Science Closed
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Continuous and autonomous measurement of total dissolved inorganic carbon (TCO2) in the oceans is critical for modelling important climate change factors such as ocean uptake of atmospheric CO2 and ocean acidification. Miniaturised chemical analysis systems are therefore required which are small enough for integration into the existing Argo ocean float network for long-term unattended depth profiling of dissolved CO2 with the accuracy of laboratory bench analysers. A microfluidic conductivity-based approach offers the potential for such miniaturisation. Reagent payload for >3 yr operation is a critical parameter. The precise injection of acid into sample, liberating CO2 from seawater, is addressed here. Laser etched microfluidic snake channel restrictors and asymmetric Y meters were fabricated to adjust the metering ratio between seawater and acid simulants. Laser etching conditions were varied to create a range of channel dimensions down to ~75 microns. Channel flow versus pressure measurements were used to determine hydrodynamic resistances which were compared with finite element simulations using a range of cross-section profiles and areas. Microfluidic metering circuits were constructed from variable resistance snake channels and dimensionally symmetric or asymmetric Y-junctions. Sample to acid volume ratios (meter ratio) up to 100:1 have been achieved with 300 microns wide snake channel for lengths > 1m. At the highest pattern resolution, this would require a footprint of > 600 mm2 (6 x10-4 m2). Circuits based solely on asymmetric Y-junctions gave meter ratios up to 16:1 with a footprint cost of < 40 mm2 and precision values of ~0.2%. Further design and fabrication refinements will be required to ensure the structural and dimensional integrity of such small channels in future integration of metering units into full TCO2 analysis microfluidic circuits.

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CO2 and HCl-induced seawater acidification impair the ingestion and digestion of blue mussel Mytilus edulis

Published 10 September 2019 Science Closed
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Highlights

1. The effect of two acidifying treatments, CO2 enrichment and HCl addition, on Mytilus edulis manifests different degrees of damage.

2. The effect of seawater acidification on mussels is not from a single factor (H+) but other action factors related to CO2.

3. Seawater acidification might inhibit the energy intake of mussels through interfering with the processes of ingestion and digestion.

Abstract

Anthropogenic CO2 emissions lead to seawater acidification that reportedly exerts deleterious impacts on marine organisms, especially on calcifying organisms such as mussels. A 21-day experiment focusing on the impacts of seawater acidification on the blue mussel, Mytilus edulis, was performed in this study, within which two acidifying treatments, CO2 enrichment and HCl addition, were applied. Two acidifying pH values (7.7 and 7.1) and the alteration of the key physiological processes of ingestion and digestion were estimated. To thoroughly investigate the impact of acidification on mussels, a histopathological study approach was adopted. The results showed that: (1) Seawater acidification induced either by CO2 enrichment or HCl addition impaired the gill structure. Transmission electron microscope (TEM) results suggested that the most obvious impacts were inflammatory lesions and edema, while more distinct alterations, including endoplasmic reticulum edema, nuclear condensation and chromatin plate-like condensation, were placed in the CO2-treated groups compared to HCl-treated specimens. The ciliary activity of the CO2 group was significantly inhibited simultaneously, leading to an obstacle in food intake. (2) Seawater acidification prominently damaged the structure of digestive glands, and the enzymatic activities of amylase, protease and lipase significantly decreased, which might indicate that the digestion was suppressed. The negative impacts induced by the CO2 group were more severe than that by the HCl group. The present results suggest that acidification interferes with the processes of ingestion and digestion, which potentially inhibits the energy intake of mussels.

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Characterization of a novel autonomous analyzer for seawater total alkalinity: results from laboratory and field tests

Published 2 September 2019 Science Closed
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High‐quality seawater total alkalinity (AT) measurements are essential for reliable ocean carbon and acidification observations. Well‐established manual multipoint potentiometric titration methods already fulfill these requirements. The next step in the improvement of these observations is the increase of the spatial and temporal measuring resolution with minimal personnel and instrumental effort. For this, a rapid, automated underway analyzer meeting the same high requirements as the traditional method is necessary. In this study, we carried out a comprehensive characterization of the flow‐through analyzer CONTROS HydroFIA® TA (Kongsberg Maritime Contros GmbH, Kiel, Germany) for automated seawater AT measurements in the laboratory and in field with overall more than 5000 measurements. Under laboratory conditions, the analyzer featured a precision of ± 1.5 μmol kg−1 and an accuracy of ± 1.0 μmol kg−1, combined in an uncertainty of 1.6 – 2.0 μmol kg−1. High precision (± 1.1 μmol kg−1) and accuracy (−0.3 ± 2.8 μmol kg−1), and low uncertainty (2.0 – 2.5 μmol kg−1) were also achieved during field trials of 4 and 6 weeks duration. Although a linear drift appears to be the typical behavior of the system, this can be corrected for by regular reference measurements giving consistent measurement results. Another advantage of regular reference measurements is the early detection of any kind of malfunction due to its direct impact on the measurement performance. Based on the present study, recommendations for automated long‐term deployments are provided in order to gain optimal performance characteristics, aiming at the requirements for AT measurements.

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Established and emerging techniques for characterising the formation, structure and performance of calcified structures under ocean acidification

Published 2 September 2019 Science Closed
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Ocean acidification (OA) is the decline in seawater pH and saturation levels of calcium carbonate (CaCO3) minerals that has led to concerns for calcifying organisms such as corals, oysters and mussels because of the adverse effects of OA on their biomineralisation, shells and skeletons. A range of cellular biology, geochemistry and materials science approaches have been used to explore biomineralisation. These techniques have revealed that responses to seawater acidification can be highly variable among species, yet the underlying mechanisms remain largely unresolved. To assess the impacts of global OA, researchers will need to apply a range of tools developed across disciplines, many of which are emerging and have not yet been used in this context. This review outlines techniques that could be applied to study OA-induced alterations in the mechanisms of biomineralisation and their ultimate effects on shells and skeletons. We illustrate how to characterise, quantify and monitor the process of biomineralisation in the context of global climate change and OA. We highlight the basic principles, as well as the advantages and disadvantages, of established, emerging and future techniques for OA researchers. A combination of these techniques will enable a holistic approach and better understanding of the potential impact of OA on biomineralisation and its consequences for marine calcifiers and associated ecosystems.

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Observing the global ocean with Biogeochemical-Argo

Published 28 August 2019 Science Closed
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Biogeochemical-Argo (BGC-Argo) is a network of profiling floats carrying sensors that enable observation of as many as six essential biogeochemical and bio-optical variables: oxygen, nitrate, pH, chlorophyll a, suspended particles, and downwelling irradiance. This sensor network represents today’s most promising strategy for collecting temporally and vertically resolved observations of biogeochemical properties throughout the ocean. All data are freely available within 24 hours of transmission. These data fill large gaps in ocean-observing systems and support three ambitions: gaining a better understanding of biogeochemical processes (e.g., the biological carbon pump and air–sea CO2 exchanges) and evaluating ongoing changes resulting from increasing anthropogenic pressure (e.g., acidification and deoxygenation); managing the ocean (e.g., improving the global carbon budget and developing sustainable fisheries); and carrying out exploration for potential discoveries. The BGC-Argo network has already delivered extensive high-quality global data sets that have resulted in unique scientific outcomes from regional to global scales. With the proposed expansion of BGC-Argo in the near future, this network has the potential to become a pivotal observation system that links satellite and ship-based observations in a transformative manner.

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