Posts Tagged 'methods'



Coral reef pH altered in situ

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

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.

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

A photonic pH sensor based on photothermal spectroscopy

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

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.

Continue reading ‘Intercomparison of four methods to estimate coral calcification under various environmental conditions’

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

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

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.

Continue reading ‘Precision pH sensor based on WO3 nanofiber-polymer composites and differential amplification’

Automated alkalinity sensing system

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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Ocean acidification in the IPCC AR5 WG II

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