Dataset: The ratio of 13C to 12C of dissolved inorganic carbon (DIC) measured during the GEOTRACES Arctic cruise (HLY 1502, ARC01) during Fall 2015

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.