Data Report Tritium and Helium Isotopes: 2015 U.S. GEOTRACES Arctic Cruise GN01 (HLY1502)

A total of 400 seawater samples from 31 hydrographic stations were collected aboard the U.S.C.G. Icebreaker HEALY between August 12, 2015, and October 7, 2015. He and Ne isotope measurements were conducted in the Noble Gas Laboratory of the Lamont-Doherty Earth Observatory on a dedicated, fully automated VG5400 mass spectrometer following the procedures described by Ludin et al., 1998. He and Ne samples were collected in copper tubes (40 ml) sealed by stainless steel pinch-off clamps. The seawater samples were first degassed in a vacuum extraction unit with an efficiency of ca. 99.9%. Gas extraction procedures are described in detail in Jenkins et al. (1991). Helium isotopes (3He and 4He) were measured using a dedicated He isotope mass spectrometer (MM5400). Air samples and blanks were used to calibrate and monitor the sensitivity changes of the instrument during operation. Measurement precision of He and Ne (units cm3 STP g-1) is ±1% of the measured values. Helium isotope ratios are reported as a δ3He or the percent deviation of the 3He/4He ratio of a sample from that of an air standard (Ratm = 1.386 x 106, Clarke et al., 1976). For high precision 3H water samples were collected in 1 liter glass bottles and analyzed by the 3He ingrowth method. 3H measurements are accurate to ± 2% or 0.05. Shipboard sampling was done by Angelica Pasqualini. Extraction work by Anthony Dachille and Richard Perry. Isotopic analysis by Tobias (Toby) Koffman.