Dataset: d13C of Dissolved Inorganic Carbon (DIC) measured on bottle cast samples from Leg 1 (Seattle, WA to Hilo, HI) of the US GEOTRACES Pacific Meridional Transect (PMT) cruise (GP15, RR1814) on R/V Roger Revelle from September to October 2018

Niskin seawater samples were collected in 250 ml bottles and poisoned with 100 µl of mercuric chloride. In the lab, approximately 100 ml was transferred from the bottle to a bubbler attached to a high vacuum line. Samples were acidified with 1 ml of 50% phosphoric acid before stripping with He gas at 200 ml min⁻¹. CO₂ gas was collected cryogenically in a liquid nitrogen cold trap after removal of water vapor. CO₂ yield was calculated manometrically (1σ = 5 µmol kg⁻¹) before transfer to a vacuum flask for isotopic analysis.