Dataset: GN01 d13C-DIC

The seawater samples were collected by transferring water from a Niskin bottle into a pre-washed and pre-baked Pyrex 250ml bottle with a ground glass top. The water was overflowed for at least one bottle volume. The sample was poisoned by adding 100uL of saturated HgCl2 solution. A greased glass stopper was inserted and rotated to insure an air tight seal. The bottle was stored at room temperature. Tests in the lab have indicated that a sample collected correctly can be stored for more than 1 year without significant offset in the d13C value.

The d13C value of dissolved inorganic carbon (DIC) in seawater was measured by: (i) drawing the seawater sample into an evacuated gravimetrically calibrated burette; (ii) transferring the sample to a helium bubbler; (iii) acidifying with 50% phosphoric acid; (iv) stripping with 99.999% pure He at a flow rate of 40 cubic cm per minute for 30 minutes and collecting the CO2 at -196 °C, after trapping out water at -78 °C. The d13C of the CO2 gas was measured on a Thermo Scientific MAT253 isotope ratio mass spectrometer. The N2O correction was less than 0.02 ‰ based on the measured mass 30/44 ratio. The d13C value is reported in per mil units (‰) relative to PDB based on working lab standards calibrated against NBS-19. The overall precision of d13C measurement was ±0.03 ‰ based on measured duplicate samples.

For complete sampling and analytical methodologies, refer to Quay et al. 2003.