Posts Tagged 'methods'

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’

A validation and comparison study of new, compact, versatile optodes for oxygen, pH and carbon dioxide in marine environments


• New optical sensors for oxygen, pH and carbon dioxide are deployed in various marine environments
• The data collected by the optical sensors are in very good agreement with the values obtained with commercially available reference systems
• Anti-biofouling strategy with copper guard is shown to be efficient for long term monitoring in highly active environments
• Compact and low cost device with autonomous logging and interchangeable sensing caps is proved to be promising for oceanographic applications


Continuous monitoring of dissolved oxygen, pH and carbon dioxide are of great importance in oceanography. Sensors are the optimal tools for in situ measurements from mobile platforms, like Autonomous Underwater Vehicles (AUVs) or Argo profiling floats, and for shipboard deployments. A validation study of small, versatile, easy-to-use, stand-alone optodes is presented. Each analyte can be read out with the identical optoelectronics which greatly minimizes the costs of the hardware needed. Several deployments were performed to evaluate the applicability of the sensors. The deployments varied in terms of duration (profiling, long-term monitoring 5 days to 8 weeks) and environmental conditions (salinity: 6–33 PSS; temperature: 9–25 °C). A set of sensors was successfully deployed at a mooring buoy, in an aquaculture facility and in the Monterey Bay Aquarium Open Sea Exhibition. They were also integrated in an AUV and a profiling float. The performance of the optodes was evaluated in comparison with commercially available sensors for dissolved oxygen (Aanderaa Data Instruments AS, Sea-Bird Scientific, OxyGuard®), pH (Hach, Satlantic) and carbon dioxide (Turner design). The data collected by our optodes and the commercially available sensors is generally in good agreement showing that the new, compact sensor device in combination with sensor foils (pO2, pH, pCO2) can be a valuable tool for many applications in oceanography. The data also revealed the importance of the calibration strategy since inappropriate calibration resulted in an offset in the measured parameter. The efficiency of simple biofouling protection strategy (copper guard) for prolong measurements in highly dynamic environments was also demonstrated.

Continue reading ‘A validation and comparison study of new, compact, versatile optodes for oxygen, pH and carbon dioxide in marine environments’

Henry’s law constant for CO2 in aqueous sodium chloride solutions at 1 atm and sub-zero (Celsius) temperatures


• Henry’s Law constant for CO2 was determined in NaCl solutions at temperatures from −1 to −10 °C.
• CO2 solubility in cold seawater and sea ice-brines is higher than previously estimated.
• Air-sea exchange of CO2 and climate modeling need to revisit the solubility of CO2 at sub-zero temperatures.


The solubility of CO2 in seawater is known to increase at colder temperatures, but few studies have examined the CO2 solubility in seawater and in sea-ice brines at sub-zero (Celsius) temperatures. The thermodynamic Henry’s Law constant (KH) for CO2 in concentrated NaCl solutions was determined for the first time at sub-zero temperatures and salinities resembling those of the cryospheric seawater and sea-ice brine environments in polar and sub-polar oceans. The temperature (T, in Kelvin) dependence of the KH within the temperature and salinity ranges of this study (263 ≤ T ≤ 272 K and 35 ≤ S ≤ 152) is described by the following best-fit equation: ln KH = −2.484 + 2.775 × 10−2(274 − T) − 9.854 × 10−2/(274 − T) − 1.009 × 10−1 ln (274–T). The results show that the general practice, in geochemical and coupled climate‑carbon cycling models, of extrapolating KH values from above-zero to sub-zero temperatures underestimates the solubility of CO2 by up to 19%.

Continue reading ‘Henry’s law constant for CO2 in aqueous sodium chloride solutions at 1 atm and sub-zero (Celsius) temperatures’

High resolution pH measurements using a lab-on-chip sensor in surface waters of northwest european shelf seas

Increasing atmospheric CO2 concentrations are resulting in a reduction in seawater pH, with potential detrimental consequences for marine organisms. Improved efforts are required to monitor the anthropogenically driven pH decrease in the context of natural pH variations. We present here a high resolution surface water pH data set obtained in summer 2011 in North West European Shelf Seas. The aim of our paper is to demonstrate the successful deployment of the pH sensor, and discuss the carbonate chemistry dynamics of surface waters of Northwest European Shelf Seas using pH and ancillary data. The pH measurements were undertaken using spectrophotometry with a Lab-on-Chip pH sensor connected to the underway seawater supply of the ship. The main processes controlling the pH distribution along the ship’s transect, and their relative importance, were determined using a statistical approach. The pH sensor allowed 10 measurements h−1 with a precision of 0.001 pH units and a good agreement with pH calculated from a pair of discretely sampled carbonate variables dissolved inorganic carbon (DIC), total alkalinity (TA) and partial pressure of CO2 (pCO2) (e.g., pHDICpCO2). For this summer cruise, the biological activity formed the main control on the pH distribution along the cruise transect. This study highlights the importance of high quality and high resolution pH measurements for the assessment of carbonate chemistry dynamics in marine waters.

Continue reading ‘High resolution pH measurements using a lab-on-chip sensor in surface waters of northwest european shelf seas’

New developments in biogeochemistry sensors: an autonomous optical sensor for high accuracy pH measurement

Ocean acidification is known to affect the growth of entire groups of species that are basic to the trophic chain, such as some zooplankton and shellfish larvae, and as such is an increasing threat for the entire ecosystem [1]. Ocean acidity is also directly related to the absorption of carbon dioxide (CO2), a major greenhouse gas and one of the key variables of the carbon cycle equation in the ocean [2]. As the concentration of CO2 in the atmosphere has increased with the advent of the industrial age, the ocean continues to play an important role in absorbing it and reducing the impact on global warming, yet at the cost of increasing ocean acidity. There are, therefore, several reasons why monitoring acidity in the ocean is essential, and several initiatives are now in place to ensure pH measurements are made on a continuous basis. For example, the Global Carbon Observing System (GCOS) provides guidance for the coordination of regional carbon-observing systems (e.g., Integrated Carbon Observation System [ICOS]), whether terrestrial, atmospheric, or oceanic, acidity being an essential variable. Tracking the decrease of ocean pH requires high-precision measurements, with sensitivity of the order of a thousandth of a pH unit (mpH) [3]. Reaching such precision is highly challenging, in particular because the stability and accuracy of most sensing techniques depend on the accurate measurement of other variables (e.g., temperature, as illustrated later). When it comes to the development of autonomous systems, additional constraints are added, like compactness, low energy consumption, and low maintenance. This chapter is engineering focused, and the authors recommend consulting the extensive scientific literature for more background on ocean carbon system science, e.g., Refs. [1–3]. The objective of the chapter is to focus on a practical solution based on optics that has been deployed successfully on moorings in the Atlantic and the Mediterranean. The system presented in this chapter has demonstrated its reliability as a high-accuracy solution for open-ocean monitoring. A detailed description of concepts of operation is provided, followed by results and analysis of future work, such as the emerging need for multifunctional capabilities.

Continue reading ‘New developments in biogeochemistry sensors: an autonomous optical sensor for high accuracy pH measurement’

Preparation and optimization of optical pH sensor based on sol-gel

Making use of the sol-gel technique, an optical pH sensor was prepared, which was made from an organic carrier with four indictors including congo red, bromophenol blue, cresol red, and chlorophenol red, cross-linked by tetraethyl orthosilicate (TEOS) and cellulose acetate. The actual detection range of the optical pH sensor is 2.5–11.0. The optimal ratio of ethyl orthosilicate, absolute ethanol, deionized water, and hydrochloric acid in glue precursor of the sensor-sensitive membrane was explored. The orthogonal experiment was designed to optimize the dosage of cellulose acetate, N,N-dimethylformamide (DMF), indicator, hydrochloric acid, and precursor glue in preparing the sensor-sensitive membrane. The linearity, measurement accuracy, repeatability, stability, and response time of the prepared pH sensor were tested. The measurement results were analyzed using a support vector machine and linear regression. The experimental results show that the optical pH sensor has a measurement accuracy of up to 0.2 pH and better stability and repeatability than the traditional pH glass electrode.

Continue reading ‘Preparation and optimization of optical pH sensor based on sol-gel’

Robust constraints on past CO2 climate forcing from the boron isotope proxy

The atmospheric concentration of the greenhouse gas carbon dioxide, CO2, is intimately coupled to the carbon chemistry of seawater, such that the radiative climate forcing from CO2 can be changed by an array of physical, geochemical and biological ocean processes. For instance, biological carbon sequestration, seawater cooling and net CaCO3 dissolution are commonly invoked as the primary drivers of CO2 change that amplify the orbitally‐paced ice age cycles of the late Pleistocene. Based on first‐principle arguments with regard to ocean chemistry we demonstrate that seawater pH change (∆pH) is the dominant control that effectively sets CO2 radiative forcing (∆F) on orbital timescales, as is evident from independent late Pleistocene reconstructions of pH and CO2. In short, all processes relevant for CO2 on orbital timescales, including temperature change, cause pH to change to bring about fractional CO2 change so as to yield a linear relationship of ∆pH to CO2 climate forcing. Further, we show that ∆pH and CO2 climate forcing can be reconstructed using the boron isotope pH‐proxy more accurately than absolute pH or CO2, even if seawater boron isotope composition is poorly constrained and without information on a second carbonate system parameter. Thus, our formalism relaxes otherwise necessary assumptions to allow the accurate determination of orbital timescale CO2 radiative forcing from boron isotope‐pH reconstructions alone, thereby eliminating a major limitation of current methods to estimate our planet’s climate sensitivity from the geologic record.

Continue reading ‘Robust constraints on past CO2 climate forcing from the boron isotope proxy’

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Ocean acidification in the IPCC AR5 WG II

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