Posts Tagged 'methods'

Pressure compensated pH sensor (United States Patent)

Inventors: Daryl Allen Carlson, Jesse John Bauman, David Dahl Walter, Matthew Eric D’Asaro

An embodiment a pressure compensated pH sensor apparatus, including: a pH sensing component comprising a sensing portion that is exposed to a fluid source when in use; a pressure chamber located in a position under the sensing portion and that envelopes all of the sensing portion not exposed to the fluid source when in use; and a pressure compensation mechanism located within the pressure chamber, wherein the pressure compensation mechanism reacts to pressure from an environment outside the apparatus, thereby support the sensing portion.

Continue reading ‘Pressure compensated pH sensor (United States Patent)’

Ultrasensitive seawater pH measurement by capacitive readout of potentiometric sensors

Potentiometric pH probes remain the gold standard for the detection of pH but are not sufficiently sensitive to reliably detect ocean acidification at adequate frequency. Here, potentiometric probes are made dramatically more sensitive by placing a capacitive electronic component in series to the pH probe while imposing a constant potential over the measurement circuit. Each sample change now triggers a capacitive current transient that is easily identified between the two equilibrium states, and is integrated to reveal the accumulated charge. This affords dramatically higher precision than with traditional potentiometric probes. pH changes down to 0.001 pH units are easily distinguished in buffer and seawater samples, at a precision (standard deviation) of 28 μpH and 67 μpH, respectively, orders of magnitude better than what is possible with potentiometric pH probes.

Continue reading ‘Ultrasensitive seawater pH measurement by capacitive readout of potentiometric sensors’

Shallow coral reef free ocean carbon enrichment: novel in situ flumes to manipulate pCO2 on shallow tropical coral reef communities

Given the severe implications of climate change and ocean acidification (OA) for marine ecosystems, there is an urgent need to quantify ecosystem function in present‐day conditions to determine the impacts of future changes in environmental conditions. For tropical coral reefs that are acutely threatened by these effects, the metabolism of benthic communities provides several metrics suitable for this purpose, but the application of infrastructure to manipulate conditions and measure community responses is not fully realized. To date, most studies of the effects of OA on coral reefs have been conducted ex situ, and while greater ecological relevance can be achieved through free ocean carbon enrichment (FOCE) experiments on undisturbed areas of reef, such approaches have been deterred by technical challenges (e.g., spatial scale and duration, stable maintenance of conditions). In this study, we describe novel experimental infrastructure called shallow coral reef (SCoRe) FOCE to overcome these challenges and present data from a proof of concept application in Mo’orea, French Polynesia. Our objectives were to (1) implement an autonomous system that could be deployed kilometers from shore, (2) regulate the chemical (pCO2) and physical properties of seawater over undisturbed, shallow (∼2–5‐m depth) coral reef over multiple weeks, and (3) measure the metabolic response of the coral community to the treatment conditions. We describe the design, function, and application of the SCoRe FOCE, and present data demonstrating its efficacy. This infrastructure has great potential for advancing ecologically relevant studies of the effects of changing environmental conditions on coral reefs.

Continue reading ‘Shallow coral reef free ocean carbon enrichment: novel in situ flumes to manipulate pCO2 on shallow tropical coral reef communities’

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

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 for this process, the study was performed under two starting pH levels (ambient: 8.05 and low: 7.2) 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 (update)’

Autonomous, ISFET-based total alkalinity and pH measurements on a barrier reef of Kāneʻohe Bay

Here we present first of its kind high frequency Total Alkalinity (AT) and pH data from a single solid-state autonomous sensor collected during a 6-day deployment at a barrier reef in Kāneʻohe Bay on the CRIMP-2 buoy. This dual parameter sensor is capable of rapid (<60 s), near simultaneous measurement of the preferred seawater carbonate system parameters, pH and AT without requiring any external reagents or moving parts inherent to the sensor. Its solid state construction, low power consumption, and low titrated volume (nanoliters) requirement make this sensor ideal for in situ monitoring of the aqueous carbon dioxide system. Through signal averaging, we estimate the pH-AT sensor is capable of achieving 2-10 μmol kg-1 precision in AT and 0.005 for pH. The CRIMP-2 site in Hawaiʻi provided an excellent means of validation of the prototype pH-AT sensor due to the extensive observations routinely collected at this site and large daily fluctuations in AT (~116 μmol kg-1) driven primarily by high calcification during the day and occasional CaCO3 mineral dissolution at night. High frequency sampling by the pH-AT sensor reveals details in the diurnal cycle that are nearly impossible to observe by discrete sampling. Greater temporal resolution of the aqueous carbon dioxide system is essential for differentiating various drivers of coral reef health and the response to external influences such as ocean warming and acidification.

Continue reading ‘Autonomous, ISFET-based total alkalinity and pH measurements on a barrier reef of Kāneʻohe Bay’

The ebb and flow of protons: a novel approach for the assessment of estuarine and coastal acidification


• Proton production and transport are responsible for estuarine acidification.

• Proton fluxes (mmol/h) were quantified between an estuary and bay.

• Fluxes calculated using high frequency [H+] and tidal discharge measurements.

• Non-tidal proton fluxes are directed upstream with seasonal changes in magnitude.

• Delaware Bay contributes to the acidification of the Murderkill Estuary.


The acidification of coastal waters is a consequence of both natural (e.g., aerobic respiration) and anthropogenic (e.g., combustion of fossil fuels, eutrophication) processes and can negatively impact the surrounding ecosystems. Until recently it was difficult to accurately measure estuarine pH, and thus total proton concentrations (), when salinities vary significantly and rapidly as a consequence of tidal mixing. Proton production and transport are ultimately responsible for acidification in coastal environments, and the uncertainty surrounding proton concentrations measured at high frequency has hindered our understanding of the net impact of global and local processes on estuarine acidification. Here, we quantify the rate of proton exchange between an estuary and bay to assess the extent of acidification by using the novel combination of high frequency pHT (total hydrogen ion concentration scale) data from an autonomous SeapHOx™ sensor and continuous tidal discharge measurements made between the eutrophic Murderkill Estuary and Delaware Bay. Proton fluxes reverse with each tide. However, the net non-tidal proton fluxes are directed upstream and display seasonal changes in magnitude. Our results indicate that Delaware Bay contributes to the acidification of the Murderkill Estuary, yet the degree of acidification is reduced in the summer. Using proton concentrations measured at high temporal resolution to calculate proton fluxes provides a new and relatively simple approach for quantifying the acidification of dynamic nearshore environments.

Continue reading ‘The ebb and flow of protons: a novel approach for the assessment of estuarine and coastal acidification’

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


• 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.


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’

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Ocean acidification in the IPCC AR5 WG II

OUP book