Mass Spectrometer

Measurements of dissolved gas concentrations such as carbon dioxide, methane, and hydrogen sulfide are critical to understanding volcanic, chemical, and biological processes in submarine environments. Carbon dioxide in magma chambers helps drive seafloor eruptions, and, along with methane and hydrogen sulfide, is key to supporting the subseafloor biosphere. Until recently, however, it has been impossible for scientists to measure these gases in situ for long-periods of time. Scientists depended on taking individual samples from vents and seeps, and then analyzing them back in land-based laboratories.

Two novel mass spectrometers, developed by Peter Girguis at Harvard University, are installed on the Cabled Array, providing real-time measurements of gases with live transmission of the data to shore. One was installed in the diffuse vent site called El Gordo from 2014-2017 in the International District hydrothermal vent field at the summit of Axial Seamount. During the summer of 2017, it was moved to the Tiny Village site, also in the International District. A second mass spectrometer has been deployed at Southern Hydrate Ridge since 2014. In concert, these instruments will provide the first, real-time long-term measurements of gases in both vent and seep environments, providing critical new information about gas evolution in these dynamic systems.

The mass spectrometer instrument class produces two core data products on OOI: Level 1 Dissolved Gas Concentrations (DISSGAS) and Level 2 Total Gas Concentration (TOTLGAS). The data for the computation of the L1 core data product are derived from the Residual Gas Analyzer (RGA) integrated in the mass spectrometer instrument. The resulting L1 DISSGAS core data product is calculated from the L0 Mass Spectral Intensities and the sample temperature, also measured by the mass spectrometer instrument, and is composed of the dissolved concentrations (uM) of the individual gases: methane, ethane, hydrogen, argon, hydrogen sulfide, oxygen and carbon dioxide. The L2 TOTLGAS core data product is calculated from the individual dissolved gas concentrations, the inlet fluid temperature, and the pH of the fluid also measured by the mass spectrometer, and is composed of the total concentrations (uM) of the individual gases: hydrogen sulfide and carbon dioxide.

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