CADICA: Continuous Automated Dissolved Inorganic Carbon Analyzer with application to aquatic carbon cycle science (original) (raw)
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ISO-CADICA: Isotopic Continuous Dissolved Inorganic Carbon Analyser
RATIONALE: Quantifying the processes that control dissolved inorganic carbon (DIC) dynamics in aquatic systems is essential for progress in ecosystem carbon budgeting. The development of a methodology that allows high-resolution temporal data collection over prolonged periods is essential and is described in this study. METHODS: A novel sampling instrument that sequentially acidifies aliquots of water and utilises gas-permeable ePTFE tubing to measure the dissolved inorganic carbon (DIC) concentration and d13CDIC values at sub-hourly intervals by Cavity Ring-down spectrometry (CRDS) is described. RESULTS: The minimum sensitivity of the isotopic, continuous, automated dissolved inorganic carbon analyser (ISOCADICA) system is 0.01 mM with an accuracy of 0.008 mM. The analytical uncertainty in d13CDIC values is proportional to the concentration of DIC in the sample. Where the DIC concentration is greater than 0.3 mM the analytical uncertainty is 0.1 % and below 0.2 mM stability is < _ 0.3 %. The isotopic effects of air temperature, water temperature and CO2 concentrations were found to either be negligible or correctable. Field trials measuring diel variation in d13CDIC values of coral reef associated sea water revealed significant, short-term temporal changes and illustrated the necessity of this technique. CONCLUSIONS: Currently, collecting and analysing large numbers of samples for d13CDIC measurements is not trivial, but essential for accurate carbon models, particularly on small scales. The ISO-CADICA enables on-site, high-resolution determination of DIC concentration and d13CDIC values with no need for sample storage and laboratory analysis. The initial tests indicate that this system can offer accuracy approaching that of traditional IRMS analysis.
The processing, storage, and flux of inorganic carbon in rivers and streams play an influential role in the lateral transfer of atmospheric and terrestrial carbon to the marine environment. Quantifying and understanding this transfer requires a rapid and accurate means of measuring representative concentrations of dissolved inorganic carbon (DIC) and CO 2 in field settings. This paper describes a field method for the determination of DIC based on the direct measurement of dissolved CO 2 using a commercial carbonation meter. A 100-mL water sample is combined with 10 mL of a high ionic strength, low-pH, citrate buffer, mixed well, and the dissolved CO 2 concentration is measured directly. The DIC is then calculated based on the dissolved CO 2 concentration, buffer-controlled ionic strength, pH, and temperature of the mixture. The method was accurate, precise, and comparable to standard laboratory analytical methods when tested using prepared sodium bicarbonate solutions up to 40 mM DIC, North Atlantic seawater, commercial bottled waters, and carbonate spring waters. Coal mine drainage waters were also tested and often contained higher DIC concentrations in the field than in subsequent laboratory measurements; the greatest discrepancy was for the high-CO 2 samples, suggesting that degassing occurred after sample collection. For chemically unstable waters and low-pH waters, such as those from high-CO 2 mine waters, the proposed field DIC method may enable the collection of DIC data that are more representative of natural settings.
Rapid Communications in Mass Spectrometry, 2006
We present here an improved and reliable method for measuring the concentration of dissolved inorganic carbon (DIC) and its isotope composition (δ13CDIC) in natural water samples. Our apparatus, a gas chromatograph coupled to an isotope ratio mass spectrometer (GCIRMS), runs in a quasi-automated mode and is able to analyze about 50 water samples per day. The whole procedure (sample preparation, CO2(g)–CO2(aq) equilibration time and GCIRMS analysis) requires 2 days. It consists of injecting an aliquot of water into a H3PO4-loaded and He-flushed 12 mL glass tube. The H3PO4 reacts with the water and converts the DIC into aqueous and gaseous CO2. After a CO2(g)–CO2(aq) equilibration time of between 15 and 24 h, a portion of the headspace gas (mainly CO2+He) is introduced into the GCIRMS, to measure the carbon isotope ratio of the released CO2(g), from which the δ13CDIC is determined via a calibration procedure. For standard solutions with DIC concentrations ranging from 1 to 25 mmol · L−1 and solution volume of 1 mL (high DIC concentration samples) or 5 mL (low DIC concentration samples), δ13CDIC values are determined with a precision (1σ) better than 0.1‰. Compared with previously published headspace equilibration methods, the major improvement presented here is the development of a calibration procedure which takes the carbon isotope fractionation associated with the CO2(g)–CO2(aq) partition into account: the set of standard solutions and samples has to be prepared and analyzed with the same ‘gas/liquid’ and ‘H3PO4/water’ volume ratios. A set of natural water samples (lake, river and hydrothermal springs) was analyzed to demonstrate the utility of this new method. Copyright © 2006 John Wiley & Sons, Ltd.
Assessing carbon dynamics in natural and perturbed boreal aquatic systems
Journal of Geophysical Research, 2012
1] Most natural freshwater lakes are net greenhouse gas (GHG) emitters. Compared to natural systems, human perturbations such as watershed wood harvesting and long-term reservoir impoundment lead to profound alterations of biogeochemical processes involved in the aquatic cycle of carbon (C). We exploited these anthropogenic alterations to describe the C dynamics in five lakes and two reservoirs from the boreal forest through the analysis of dissolved carbon dioxide (CO 2 ), methane (CH 4 ), oxygen (O 2 ), and organic carbon (DOC), as well as total nitrogen and phosphorus. Dissolved and particulate organic matter, forest soil/litter and leachates, as well as dissolved inorganic carbon were analyzed for elemental and stable isotopic compositions (atomic C:N ratios, d 13 C org , d 13 C inorg and d 15 N tot ). We found links between the export of terrestrial organic matter (OM) to these systems and the dissolved CO 2 and O 2 concentrations in the water column, as well as CO 2 fluxes to the atmosphere. All systems were GHG emitters, with greater emissions measured for systems with larger inputs of terrestrial OM. The differences in CO 2 concentrations and fluxes appear controlled by bacterial activity in the water column and the sediment. Although we clearly observed differences in the aquatic C cycle between natural and perturbed systems, more work on a larger number of water bodies and encompassing all four seasons should be undertaken to better understand the controls, rates, and spatial as well as temporal variability of GHG emissions, and to make quantitatively meaningful comparisons of GHG emissions (and other key variables) from natural and perturbed systems.
Limnology and Oceanography: Methods, 2019
We report results of an intercomparison of stable carbon isotope ratio measurements in seawater dissolved inorganic carbon (δ 13 C-DIC) which involved 16 participating laboratories from various parts of the world. The intercomparison involved distribution of samples of a Certified Reference Material for seawater DIC concentration and alkalinity and a preserved sample of deep seawater collected at 4000 m in the northeastern Atlantic Ocean. The between-lab standard deviation of reported uncorrected values measured with diverse analytical, detection, and calibration methods was 0.11‰ (1σ). The multi-lab average δ 13 C-DIC value reported for the deep seawater sample was consistent within 0.1‰ with historical measured values for the same water mass. Application of a correction procedure based on a consensus value for the distributed reference material, improved the between-lab standard deviation to 0.06‰. The magnitude of the corrections were similar to those used to correct independent data sets using crossover comparisons, where deep water analyses from different cruises are compared at nearby locations. Our results demonstrate that the accuracy/ uncertainty target proposed by the Global Ocean Observing System (AE0.05‰) is attainable, but only if an aqueous phase reference material for δ 13 C-DIC is made available and used by the measurement community. Our results imply that existing Certified Reference Materials used for seawater DIC and alkalinity quality control are suitable for this purpose, if a "Certified" or internally consistent "consensus" value for δ 13 C-DIC can be assigned to various batches. The concentration and stable carbon isotope composition of dissolved inorganic carbon in ocean waters, referred to henceforth as DIC and δ 13 C-DIC, respectively, are influenced by several important physical and biogeochemical processes including biological uptake and release of inorganic carbon, mixing of water masses and air-sea CO 2 exchange. This makes δ 13 C-DIC a useful tracer for which the geographic and temporal distribution contains information about ocean carbon cycle processes as well
Environmental Science & Technology, 2015
A new, in-situ sensing system, Channelized Optical System (CHANOS), was recently developed to make high-resolution, simultaneous measurements of total dissolved inorganic carbon (DIC) and pH in seawater. Measurements made by this single, compact sensor can fully characterize the marine carbonate system. The system has a modular design to accommodate two independent, but similar measurement channels for DIC and pH. Both are based on spectrophotometric detection of hydrogen ion concentrations. The pH channel uses a flowthrough, sample-indicator mixing design to achieve near instantaneous measurements. The DIC channel adapts a recently developed spectrophotometric method to achieve flow-through CO 2 equilibration between an acidified sample and an indicator solution with a response time of only ~90s. During laboratory and in-situ testing, CHANOS achieved a precision of ±0.0010 and ±2.5 µmol kg-1 for pH and DIC, respectively. In-situ comparison tests indicated that the accuracies of the pH and DIC channels over a three-week time-series deployment were ±0.0024 and ±4.1 µmol kg-1 , respectively. This study demonstrates that CHANOS can make in-situ, climatology-quality measurements by measuring two desirable CO 2 parameters, and is capable of resolving the CO 2 system in dynamic marine environments.