Sampling Gases from the Seafloor: Rock-Microbe Linkages

Clues to Earth’s Early History?
During this mission, we will be learning about the gas compositions of the vent fluids. These gases may be very important for energy and cell building in the organisms living in and around the vents. Our samples may provide hints as to what some of the gases were like in hydrothermal systems operating very early on in the Earths history.

Collecting Samples for Gas Analysis and Extraction
We will be using specialized titanium gas-tight samplers to collect hydrothermal vent fluids for gas extraction and analyses. These samplers are evacuated prior to use to minimize the contamination by air in any sample and they remain sealed after sampling to prevent loss of gas if the fluids degas on ascent for some reason (cooling and/or shrinking occur with high-temperature hydrothermal vent samples). In the past, we have found that traditional vent sampling syringes (“major samplers”) can lose gas as they depressurize on ascent.

In the Shipboard Lab
In the lab the samplers are connected to a vacuum extraction line and the fluids are dumped from the sampler into a flask where all gases are “boiled” (low temperature vacuum extraction) out of the fluid. This “whole” gas sample is dried (of water vapor) and moved to calibrated volumes for a pressure measurement. That allows calculation of a “total gas” number for the sample which is used with later component analyses to determine dissolved concentrations for the various gas species.

Shore-based Analysis
The gas mix is then sub-sampled into glass ampules (small glass tubes that are sealed by melting the glass using a very hot flame after the gas is transported into them) for later analyses onshore. The water is saved for elemental analyses by the fluid chemists.

Back in the shore-based laboratories a number of different analyses take place on the gas sub-samples. A measurement is made of the different components in the gas mix by gas chromatography. We are able to analyze for Ne,H2,N2,O2,Ar,CO,CH4 and CO2 routinely and generally estimate H2S as the unanalyzed remainder.

Onshore Mass Spectrometry
Mass spectrometry is used for analysis of helium isotopes. These isotopes are important indicators of magmatic processes happening below the sea-floor. Onshore laboratories will also be using mass spectrometry to look at Carbon 13 and Carbon 14 isotope values in the dissolved gases from these vents. These isotopes can provide some age and process information.