Dataset: Helium isotope with helium and neon concentration data 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

Water samples were transferred from Niskin bottles and stored in crimped copper tubing. Gases were extracted from the water samples in a shore-based vacuum system and stored in aluminosilicate glass ampoules. The extracted gases were analyzed for helium and neon concentrations using ion counting in a quadrupole mass spectrometer and for helium isotopes using a magnetic sector dual-collecting isotope ratio mass spectrometer. Details are given in Jenkins et al. (2019) and Stanley et al. (2007).

Note: Natural and bomb tritium will decay to 3He in the copper tubing water sample container between the time the water sample was acquired and when the gases were extracted. We account for this using tritium concentrations estimated from a prior (2015) cruise occupation extrapolated in time and interpolated in space to the sample location and time. The size of this effect is significant in shallow, northern waters and vanishingly small in deeper and more southerly waters.