Field sampling
A total of 145 seawater samples were collected from 23 hydrographic stations aboard the Alkor (AL510) cruise from June 6 to June 11, 2018. Samples were secured in 40 milliliter copper tubes 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% to extract the dissolved gases helium (He) and neon (Ne). He and Ne were then isolated by cold trapping on activated charcoal.

Laboratory measurements
Helium (He) and Neon (Ne) gas samples were analyzed at the Lamont-Doherty Earth Observatory (LDEO) Noble Gas Laboratory on a dedicated, fully automated VG5400 quadrupole mass spectrometer following the procedures described by Ludin et al. (1998). A fraction of the helium and neon was admitted into a quadrupole analyzer for helium and neon measurements. Separation of neon from helium was achieved using a cryogenic trap, and the separated helium was admitted into the isotope mass spectrometer for isotopic analysis. Air samples and blanks were used to calibrate and monitor the sensitivity changes of the instrument during operation. He and Ne are reported in units of cubic centimeters at standard temperature and pressure per gram (cm3 STP g-1) where standard temperature and pressure is 0 degrees, 101.325 kPa. The precision of the helium and neon concentrations is ±1% of the measured value. Helium isotope ratios were measured with precision of ca. 0.2% and reported as d3He or the percent deviation of the 3He/4He ratio of a measured sample from that of an air standard (Ratm = 1.386 x 106; Clarke et al., 1976).

Processing DRIs (directly responsible individuals):
Shipboard sampling was done by Tobias (Toby) Koffman.
Helium extraction work and isotopic analysis by Tobias (Toby) Koffman.
Data processing by Peter Schlosser.

Problems/Issues
Some samples (indicated in the data table) contained excess air trapped in the copper tube during sampling.
Station 31, AL510_CTD_043, 3100007
Station 31, AL510_CTD_042, 3100006
Station 44, AL510_CTD_107, 4400011
Station 52, AL510_CTD_135, 5200003
Station 54, AL510_CTD_155, 5400011
Station 68, AL510_CTD_227, 6800011
Station 70, AL510_CTD_233, 7000005