Dataset: SF6 and helium data from a tracer release experiment conducted June 2018 in the coastal Baltic Sea during FS Alkor cruise AL510

A tracer release experiment was conducted in the coastal Baltic Sea during cruise AL510 aboard the research vessel FS Alkor. On June 4th, 2018, we injected 3He and SF6 into the surface ocean (~5 m depth). After the injection, near the center of the SF6 patch, depth profiles of temperature and salinity were measured using a conductivity, temperature, and depth (CTD) sonde and water samples were collected in Niskin bottles.

Discrete SF6 samples (and replicates) were drawn from the Niskin bottles using 550 ml glass bottles with ground-glass stoppers. For discrete 3He samples, ~40 milliliters of seawater were collected in copper tubes mounted in aluminum channels and sealed at the ends with stainless steel clamps.

SF6 samples were taken at the same stations and measured on board the FS Alkor. Concentration of SF6 was measured using a purge-and-trap SF6 analysis system designed following Law et al. (1994). In this system, SF6 was separated from other gases and measured with a gas chromatography electron capture detector (GC-ECD).

3He samples were measured at the Lamont-Doherty Earth Observatory (LDEO) Noble Gas Laboratory.  In the laboratory, 3He samples were extracted from the copper tubes using a vacuum extraction system (Ludin et al., 1998) and measured on a VG-5400 He isotope mass spectrometer. Precision is about 0.5 to 1% in δ3He for samples with high δ3He values (100% < δ3He < 1000%), and 0.2 to 0.5% for samples with lower δ3He values (-1.7% < δ3He < 100%).