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Inorganic Carbon

Overview

Inorganic carbon samples will be weighed and directly acidified in our Sample Prep Lab.

Coral

Coral Pieces

Corals, like tree-rings, and sometimes molluscs, have annual growth bands and can be sampled according to the years of growth. A good sample size for carbonates is approximately between 8 and 12 milligrams.

To estimate the milligrams of carbon in carbonate, use the formula mg C = mg CaCO3/8.33 then multiply by 0.9 to account for impurities. When requested, a 10 % split of the CO2 generated is taken for in-line stable isotope measurement. Process used Acidification.

Foraminifera

Microscopic photo of a mixed assemblage of foraminifera

If pure, a 4 mg sample will conservatively yield approximately 430 micrograms of carbon (0.004g * 0.9 yield / 8.33 MW carbonate). When requested, a 10% split of the CO2 generated is taken for in-line stable isotope measurement (430-43 µg ). Samples that yield < 100 micrograms of carbon will require small sample processing.

If there is sediment on and in the forams that contains carbonate of a different age than the forams, it will skew the radiocarbon result. Some submitters sonicate forams in a 3% peroxide and sodium hexametaphosphate solution and rinse with DH2O to clean tests. Take care to inspect the sample immediately prior to submitting and to remove anything that is not a foram, including fibers, hair or quartz grains. The smaller the sample, the larger the potential impact of small bits of contamination on the isotope concentration. Process used Acidification.

Dissolved Inorganic Carbon

DIC samples undergoing "water-stripping" process

Ocean, lake, pond, ground or pore water.

Beginning with sample collection, it is extremely important that all of the materials coming into contact with the water are as 14C-free as possible. Post-collection biological activity can alter the carbon isotopic concentration of the samples. Addition of a saturated mercuric chloride solution will kill all bacteria (typically used for seawater samples), but this may not be appropriate for your sampling situation. Other poisons should be discussed with us if you choose not to use HgCl2. If the sulphur content in the water is greater than that of standard seawater, then you may need additional poison.

DIC Sample Bottles

Our preferred DIC sample collection vessel is a Wheaton 29/22, 100 ml borosilicate glass bottle (VWR bottle#W216015 ) with a high-quality ground-glass stopper (54 x 110 mm). The stopper is lubricated prior to collection with Apiezon grease to prevent exchange with the atmosphere. We may be able to supply bottles for your sample collection - please contact us for more information and refer to the collection protocols for full specifications. A shipping account number will be required to return sample bottles.

The DIC concentration must be supplied or estimated in order for us to extract an appropriate mass of carbon from a water sample. Process used Water Stripping or REDICS.

Related Files

Mollusc

Mollusc

Mollusc samples are typically quite large and require subsampling to prepare an AMS sample. When there is the luxury of excess material, use it to prepare a pristine portion of the inner shell by scraping, cutting or grinding away the sometimes chalky outer portions of the shell that are most susceptible to recrystallization. Consider sampling across growth-bands for a representative sample, or using the inner or outer year growth parts only for a more age-constrained sample.

Treating carbonates with a mild acid leach prior to submission is not recommended because this procedure is best done immediately prior to the full acid hydrolysis. Over time, an etched surface may adsorb CO2 from the air. If there is enough material and you want to remove the surface portion of your shell, an acid etch/leach may be requested on the submittal form. Process used Acidification.

Sediment (carbonates)

Ground, dried sediment

The inorganic carbon content of sediments can vary considerably. We need at least an approximate idea of the %CaCO3 of sediment before we can treat it. Without this information, we will not be able to process the samples.

Submit dry sediment samples in well-labeled, clean glass or plastic containers. We assume samples are homogeneous. Some submitters dry and grind sediment samples prior to submission to ensure homogeneity. Process used Acidification.