The In-Spectr was recently deployed at Saanich Inlet, Canada. As is common in fjords, the bottom layer of the inlet is isolated from the ocean by a shallow sill at the entrance. Deep water in the inlet is only partially replenished every 2-3 years by conditions that develop during neap tides in the late summer. Due to degradation of organic material, the inlet’s deep water is typically anoxic, and rich in methane, carbon dioxide, and sulfur compounds.

The instrument was deployed on a cable and lowered to depths slightly in excess of 200m. While the intention of the deployment was to demonstrate the instrument’s response to methane, profiles of several gases were obtained simultaneously.  Photographs show the method of deployment. The yellow tether provides power and communication to the mass spectrometer, and a Conductivity-Temperature-Depth sensor provides conjugate real-time determinations of general environmental conditions.

In the graph below, a time series plots numerous gases showing strong variations through time. Instrument response was smoothed to remove high frequency noise. Strong changes in m/z 15 (methane) were detected at various depths below 100m, while other species were homogenous in the Saanich Inlet bottom layer.

Finally, depth profiles were obtained for multiple gases during a single cast, and correlated with depth. Data collection times were offset by 270s to account for the period between sample acquisition and subsequent transfer of gas across the membrane. Data were interpolated at a frequency of 1Hz and binned into 1m depth increments.

Visible in the graph on the next page, a thermocline was detected at 100m as the the instrument entered the anoxic bottom water. This produced a sharp decline in m/z 32 (oxygen) to background levels. Conversely, m/z 44 (carbon dioxide) had a very sharp increase, which included a reproducible maximum at 120m. Beginning at 100m, m/z 15 (methane) increased steadily with depth. Profiles for m/z 34 were highly correlated with m/z 32 (oxygen), until a depth of 140m. Below this depth a significant increase in m/z 34 is attributed to hydrogen sulfide concentrations. At depths below 140m an increase in m/z 48 pointed to the production of sulfur dioxide.

Please click here for a *.pdf document providing full details of the results of the In-Spectr Saanich Inlet methane studies.