Dataset: GN01 Silicon Stable Isotopes
Deployment: HLY1502

Samples collected from Niskin bottles using the GEOTRACES ODF CTD-rosette system. (Note on niskin trip depths reported in dataset: multiple bottles were tripped to collect sample water; these samples were linked to the Niskin number having both oxygen and salinity bottle data.)

Seawater samples for δ30Si measurements were collected using a Oceanographic Data Facilitiy’s (ODF, Scripps Institution of Oceanography) CTD-rosette mounted with Niskin samplers and a Sea-Bird Electronics CTD (SBE9plus). Seawater was gravity filtered into polypropylene containers through in-line Supor filter capsules (0.8/0.45 µm) attached directly to each Niskin bottle. Sample bottles were capped and stored without preservative in the dark.

Back in the laboratory, the silicon from seawater was precipitated of as trimethylamine silicomolybdate using a high purity triethlyamine ammonium molybdate solution (TEA-Moly). The precipitate was isolated by filtration onto a polycarbonate filter and purified by high temperature combustion to produce solid silicon dioxide. SiO2 was then converted to solid Cs2SiF6 by dissolution in HF and addition of CsCl. The Cs2SiF6 was rinsed with ethanol, dried and dissolved in high purity (>18MΩ) water. BaSiF6 was precipitated by the addition of BaCl, rinsed with ethanol and dried.

Isotopic ratio analysis was performed using a Nu Perspective isotope ratio mass spectrometer equipped with a Nu Sil inlet system. Samples as BaSiF6 are loaded into sample vials that are placed in a sample carousel in the Nu Sil. Samples are sequentially heated to 590°C.

Isotope delta values are normalized against the international standard NBS28.

For more information, see the Protocol document (under Supplemental Files).