Total Inorganic Carbon Measurements Research Articles

Measurements of the dissolved inorganic carbon system and associated biogeochemical parameters in the Canadian Arctic, 1974–2009

Abstract. We have assembled and conducted primary quality control on previously publicly unavailable water column measurements of the dissolved inorganic carbon system and associated biogeochemical parameters (oxygen, nutrients, etc.) made on 26 cruises in the subarctic and Arctic regions dating back to 1974. The measurements are primarily from the western side of the Canadian Arctic, but also include data that cover an area ranging from the North Pacific to the Gulf of St. Lawrence. The data were subjected to primary quality control (QC) to identify outliers and obvious errors. This data set incorporates over four thousand individual measurements of total inorganic carbon (TIC), alkalinity, and pH from the Canadian Arctic over a period of more than 30 years and provides an opportunity to increase our understanding of temporal changes in the inorganic carbon system in northern waters and the Arctic Ocean. The data set is available for download on the CDIAC (Carbon Dioxide Information Analysis Center) website: http://cdiac.ornl.gov/ftp/oceans/IOS_Arctic_Database/ (doi:10.3334/CDIAC/OTG.IOS_ARCT_CARBN).

Estimation of Chlorella vulgaris growth rate in a continuous photobioreactor

AbstractMicroalgae consume carbon dioxide for their growth and to produce secondary metabolites. One of the control system challenges is to maximize this carbon dioxide consumption by controlling microalgae growth, and by maintaining its growth rate at an optimal value. However, there is no such thing as a microalgae growth rate sensor. This paper proposes a software sensor for the specific growth rate and biomass concentration of a microalgae culture in a continuous photobioreactor using the measurements of Total Inorganic Carbon in the medium. Numerical simulations are included to illustrate the performance of the proposed estimation strategy.

Spectrophotometric measurement of total inorganic carbon in aqueous solutions using a liquid core waveguide

This work describes spectrophotometric procedures for direct measurements of total inorganic carbon in aqueous solutions. The procedures used for these measurements involve CO 2 equilibration across the permeable wall of a Teflon AF-2400 liquid core waveguide. The waveguide acts as both an equilibration membrane and an optical cell in which spectrophotometric pH measurements, obtained via measurements of absorbance ratios, are used to determine the CO 2 fugacity and total carbon in acidified solutions surrounding the waveguide. Total carbon concentrations ( C T) a in the acidified external medium are calculated using the equation: log(C T ) a = log (K 0) a (K 0) i +B(t)− log R−e 1 1−Re 3/e 2 where B( t) is an empirically derived constant, ( K 0) a and ( K 0) i are Henry’s law constants appropriate to the acidified external solution (a) and a solution inside the waveguide (i) whose total alkalinity is known, R is an absorbance ratio of bromocresol purple (BCP) at 589 and 432 nm, and both e 1 and e 3/ e 2 are molar absorptivity ratios appropriate to bromocresol purple. Spectrophotometric ( C T) a measurements of natural riverine samples obtained using the procedures described in this work are in good agreement with C T measurements obtained via coulometry.

Coulometric total carbon dioxide analysis for marine studies: assessment of the quality of total inorganic carbon measurements made during the US Indian Ocean CO2 Survey 1994–1996

Two single-operator multiparameter metabolic analyzers (SOMMA)-coulometry systems (I and II) for total carbon dioxide (TCO2) were placed on board the R/V Knorr for the US component of the Indian Ocean CO2 Survey in conjunction with the World Ocean Circulation Experiment-WOCE Hydrographic Program (WHP). The systems were used by six different measurement groups on 10 WHP Cruises beginning in December 1994 and ending in January 1996. A total of 18,828 individual samples were analyzed for TCO2 during the survey. This paper assesses the analytical quality of these data and the effect of several key factors on instrument performance. Data quality is assessed from the accuracy and precision of certified reference material (CRM) analyses from three different CRM batches. The precision of the method was 1.2 μmol/kg. The mean and standard deviation of the differences between the known TCO2 for the CRM (certified value) and the CRM TCO2 determined by SOMMA-coulometry were −0.91±0.58 (n=470) and −1.01±0.44 (n=513) μmol/kg for systems I and II, respectively, representing an accuracy of 0.05% for both systems. Measurements of TCO2 made on 12 crossover stations during the survey agreed to within 3 μmol/kg with an overall mean and standard deviation of the differences of −0.78±1.74 μmol/kg (n=600). The crossover results are therefore consistent with the precision of the CRM analyses. After 14 months of nearly continuous use, the accurate and the virtually identical performance statistics for the two systems indicate that the cooperative survey effort was extraordinarily successful and will yield a high quality data set capable of fulfilling the objectives of the survey.

Procedure for calibration of a coulometric system used for total inorganic carbon measurements of seawater

A calibration procedure is described for measurements of total inorganic carbon (C T) in seawater using a coulometric system. In contrast to a previously published protocol which is based on pure CO 2 gas as a calibration standard, the present procedure is based on measurements of standard solutions treated similarly to seawater samples. We show that standard solutions for C T measurements can be easily prepared both in the laboratory and at sea from distilled water and preweighed sodium carbonate salt. With reasonable care, 1 l of standard solution can be used regularly over a period of a week. The precision of this calibration procedure ranges from ± 0.02 to ± 0.06%, allowing measurements of seawater samples to within ± 0.3 to ± 1.3 μmol C kg −1; such precision is necessary for detection of any increase in C T as a result of anthropogenic input. A preliminary comparison to assess the accuracy of these measurements when compared with an established manometric method performed on the same seawater shows close agreement, with a mean of 1978.4 ± 1.3 μmol C kg −1 for the coulometric method and 1978.8 μmol C kg −1 for the manometric analysis. The difference between these measurements (0.4 μmol C kg −1) is within the precision of either method. These standard solutions are simple, practical and inexpensive to prepare and measure, making them ideal for measurements at sea.

Sulfate reduction in the presence of low oxygen levels in the water column of the Cariaco Trench1,2

Precise and closely spaced alkalinity and total inorganic carbon measurements from the water column of the Cariaco Trench indicate an intense zone of sulfate reduction within the oxic waters above the O2‐H2S interface. The chemical data suggest that sulfate reduction occurs in the presence of low oxygen levels. The resulting sulfide is subsequently oxidized to S0. Although it is not clear whether or how these processes are coupled, the kinetics of redox reactions above the oxic‐anoxic interface modify the chemical distributions expected from the normal constraints of chemical equilibrium.

Seasonal effects of temperature and salinity on the partial pressure of CO2 in seawater

The exchange of CO2 between the atmosphere and the sea is of major importance to our understanding of the climatic consequences of anthropogenic CO2. Because the solubility of CO2 and the dissociation of carbonic acid in seawater are modulated by temperature and salinity, the detection of long-term changes in the oceanic carbonate system, first requires that the comparatively large short-term variations in the partial pressure of CO2 should be characterized. We present here the first direct observations of seasonal variations in the partial pressure of CO2 in the subtropical gyres of the North and South Pacific Ocean. These variations compare well with the variations predicted from observed changes in temperature and salinity using empirical equations which do not require the determination of alkalinity or total inorganic carbon, and the agreement is improved by the inclusion of air–sea exchange in the model calculations. Thus we predict that specific alkalinity within the two gyres remains extremely constant, which is confirmed by carbonate equilibrium calculations based on our measurements of total inorganic carbon.