Posts Tagged 'methods'

An ocean acidification-simulated system and its application in coral physiological studies

Due to the elevated atmospheric carbon dioxide, ocean acidification (OA) has recently emerged as a research theme in marine biology due to an expected deleterious effect of altered seawater chemistry on calcification. A system simulating future OA scenario is crucial for OA-related studies. Here, we designed an OA-simulated system (OASys) with three solenoid-controlled CO2 gas channels. The OASys can adjust the pH of the seawater by bubbling CO2 gas into seawaters via feedback systems. The OASys is very simple in structure with an integrated design and is new-user friendly with the instruction. Moreover, the OASys can monitor and record real-time pH values and can maintain pH levels within 0.02 pH unit. In a 15-d experiment, the OASys was applied to simulate OA in which the expected target pH values were 8.00, 7.80 and 7.60 to study the calcifying response of Galaxea fascicularis. The results showed daily mean seawater pH values held at pH 8.00±0.01, 7.80±0.01 and 7.61±0.01 over 15 d. Correspondingly, the coral calcification of G. fascicularis gradually decreased with reduced pH.

Continue reading ‘An ocean acidification-simulated system and its application in coral physiological studies’

A continuous-flow and on-site mesocosm for ocean acidification experiments on benthic organisms

Mesocosm experiments conducted for ecological purposes have become increasingly popular because they can provide a holistic understanding of the biological complexities associated with natural systems. This paper describes a new outdoor mesocosm designed for CO2 perturbation experiments of benthos. Manipulated the carbonate chemistry in a continuous flow-through system can be parallelized with diurnal changes, while irradiance, temperature, and nutrients can vary according to the local environment. A target hydrogen ion activity (pH) of seawater was sufficiently stabilized and maintained within 4 h after dilution, which was initiated by the ratio of CO2-saturated seawater to ambient seawater. Specifically, pH and CO2partial pressure (pCO2) levels gradually varied from 8.05–7.28 and 375–2,691 μatm, respectively, over a range of dilution ratios. This mesocosm can successfully manipulate the pH and pCO2 of seawater, and it demonstrates suitability for ocean acidification experiments on benthic communities.

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The carbon dioxide vents of Ischia, Italy, a natural system to assess impacts of ocean acidification on marine ecosystems: an overview of research and comparisons with other vent systems

As the ocean continues to take up carbon dioxide (CO2), it is difficult to predict the future of marine ecosystems. Natural CO2 vent sites, mainly of volcanic origin, that provide a pH gradient are useful as a proxy to investigate ecological effects of ocean acidification.

Continue reading ‘The carbon dioxide vents of Ischia, Italy, a natural system to assess impacts of ocean acidification on marine ecosystems: an overview of research and comparisons with other vent systems’

Carbonate ion concentrations in seawater: Spectrophotometric determination at ambient temperatures and evaluation of propagated calculation uncertainties


• A new model is presented for direct determination of [CO32−] in seawater.
• The model is appropriate for temperature 3 to 40 °C and salinity 20 to 40.
• Measured [CO32−] is best paired with CT and AT in CO2 system calculations.
• Measured [CO32−] alone can yield reliable estimates of CaCO3 saturation states.
• [CO32−] can be used in a variety of ways as a fifth measured CO2 system variable.


In ocean waters, the carbonate ion is of crucial importance to benthic and pelagic organisms that build their physical support structures out of calcium carbonate (CaCO3). Marine carbonate ion concentrations ([CO32−]) are measurable through spectrophotometric observations of the ultraviolet (UV) light absorbed by lead carbonate in Pb-enriched seawater, but previous characterizations of the Pb UV-absorption model have been applicable only at a fixed temperature of 25 °C. In this paper, the model is extended to a temperature range of 3 to 40 °C and a salinity range of 20 to 40. This advancement allows for determinations of [CO32−] with temperature measurement rather than temperature control, thus decreasing the required financial investment and instrumental complexity. The extended model also represents a significant step toward the development of automated inline or in situ [CO32−] sensors and promotes the utility of [CO32−] as a fifth measured variable for inclusion in studies of the marine carbon dioxide (CO2) system. Therefore, a quantitative evaluation of propagated uncertainties in CO2 system calculations based on [CO32−] as an input variable was also performed. The results show that total dissolved inorganic carbon (CT) and total alkalinity (AT) are the most suitable measured variables to pair with measured [CO32−] as input to such calculations. Pairing [CO32−] with the partial pressure of CO2 yields relatively low uncertainty in calculated pH — comparable to that resulting from conventional input pairs — but relatively high uncertainties in calculated AT and CT. Pairing [CO32−] with pH results in relatively high uncertainties in all calculated variables. CaCO3 saturation states (Ω) determined from measured [CO32−] (alone) can circumvent some sources of uncertainty inherent to conventional (two-variable) calculations. Simpler, more direct ways of measuring [CO32−] open up new opportunities for marine researchers and others interested in monitoring CaCO3 saturation states in seawater.

Continue reading ‘Carbonate ion concentrations in seawater: Spectrophotometric determination at ambient temperatures and evaluation of propagated calculation uncertainties’

Fast and stable optical pH sensor materials for oceanographic applications


• 4 novel optical sensor materials for pH measurements in seawater.
• 3 strategies for covalent immobilization of pH indicator into a hydrogel.
• Fast response times, excellent stability and low cross sensitivities to temperature and salinity.
• Successful application demonstration in several deployments.


The study reports preparation and detailed comparison of four new pH sensor materials for seawater measurements. The composition of the sensors is optimized in several iterations to ensure optimal dynamic range, fast response time at low temperatures, low cross-sensitivities to temperature (dpKa/dT ∼ -0.013 pH units/K) and negligible cross sensitivity to ionic strength above salinity 15 PSU. The first generation (material “pH-1″) utilizes a pH indicator which is physically entrapped into a polyurethane hydrogel. This material shows satisfactory performance only at comparably high temperatures with response times being extremely long at low temperatures (t95 > 2 h at 5 °C). The three other materials utilize cross-linked hydrophilic polymers based on poly(acryloylmorpholine) with indicator dye covalently coupled to the polymer. They feature fast response times at low temperatures (t90 < 1 min at 5 °C). Moreover, the last two generations (“pH-3″ and “pH-4″) showed no drift over 54 days at 10 °C and only a drift of 0.003 pH units/day at 25 °C. Although the stability and the sensing properties of these materials are rather similar, the synthetic effort varies considerably. The material of the fourth generation “pH-4″ explores a novel approach of covalent coupling via B–O linkage and is characterized by low synthetic effort and the pKa value optimal for seawater measurements (8.05 at 20 °C). Importantly, all new sensor materials are spectrally compatible to a recently presented seawater optode system for combined pH, pO2 and pCO2 measurements which facilitates their application in marine environment.

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Planar optode observation method for the effect of raindrop on dissolved oxygen and pH diffusion of air–water interface

The air–water interface is an important boundary where material exchanges, it has important influence on ecosystem and biogeochemical cycle. The rain can change the balance of interface, improve the exchange rate of gas flux, and make the distribution of dissolved oxygen and pH around the interface change in horizontal and vertical direction. Based on planar sensing film with highly spatial and temporal resolution which can provide the characteristics of two-dimensional distribution information, we carry out the simulation experiment of raindrops about oxygen and pH distribution in air–water interface using double parameters planar optode. The experimental data are analyzed from the gas transfer velocity, the kinetic energy flux and the sea-air flux of oxygen. The results show that rainfall process plays an important role in adjusting dissolved oxygen and pH of the surface water, the raindrop can break the balance of micro surface of water–gas interface mechanism, increase the gas transfer velocity and promote the dissolution of oxygen in the atmosphere in water to make a average increase of about 2.3 mg/L in vertical direction 23 mm. The impact of rainfall on pH of the water surface within 12 mm is relatively obvious, the pH value decreased by an average of 0.2–0.4 units, indicating that the raindrop promoted the migration of the atmosphere in the air–water interface, and the dissolved CO2 caused the surface water acidification. This study provides a novel technical method for understanding the influence of raindrops on the dissolved oxygen concentration and pH of the surface water in low wind-impacting area and static-water area.

Continue reading ‘Planar optode observation method for the effect of raindrop on dissolved oxygen and pH diffusion of air–water interface’

Routine uncertainty propagation for the marine carbon dioxide system


• Add ons to four public packages used to make CO2 system calculations were developed to make uncertainty propagation easy.

• A new type of diagram further simplifies propagating and interpreting uncertainties.

• Large changes in the uncertainties in the measured input pair of CO2 system variables often have little effect on propagated uncertainties because they are dominated by uncertainties from the equilibrium constants, particularly K1 and K2.

• Relative uncertainties for the saturation states of aragonite and calcite are larger than for the carbonate ion concentration, being dominated by the contribution of their respective solubility products.


Pairs of marine carbonate system variables are often used to calculate others, but those results are seldom reported with estimates of uncertainties. Although the procedure to propagate these uncertainties is well known, it has not been offered in public packages that compute marine carbonate chemistry, fundamental tools that are relied on by the community. To remedy this shortcoming, four of these packages were expanded to calculate sensitivities of computed variables with respect to each input variable and to use those sensitivities along with user-specified estimates of input uncertainties (standard uncertainties) to propagate uncertainties of calculated variables (combined standard uncertainties). Sensitivities from these packages agree with one another and with analytical solutions to within 0.01%; similar agreement among packages was found for the combined standard uncertainties. One package was used to quantify how propagated uncertainties vary among computed variables, seawater conditions, and the chosen pair of carbonate system variables that is used as input. The relative contributions to propagated uncertainties from the standard uncertainties of the input pair of measurements and various other input data (equilibrium constants etc) were explored with a new type of diagram. These error-space diagrams illustrate that further improvement beyond today’s state-of-the-art measurement uncertainties for the input pair would generally be ineffective at reducing the combined standard uncertainties because the contribution from the constants is larger. Likewise, using much more uncertain measurements of the input pair does not always substantially worsen combined standard uncertainty. The constants that contribute most to combined standard uncertainties are generally K1 and K2, as expected. Yet more of the propagated uncertainty in the computed saturation states of aragonite and calcite comes from their solubility products. Thus percent relative combined standard uncertainties for the saturation states are larger than for the carbonate ion concentration. Routine propagation of these uncertainties should become standard practice.

Continue reading ‘Routine uncertainty propagation for the marine carbon dioxide system’

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Ocean acidification in the IPCC AR5 WG II

OUP book