The high-resolution ocean laser-spectrometer demonstrates major technological advances in water column measurements. A new study published in Ocean Science details its first use at a site with vigorous methane release.
Text: Jessica Green
In October of 2015, Pär Jansson and his team from the Centre for Arctic Gas Hydrates, Environment, and Climate (CAGE) at UiT The Arctic University of Norway joined forces with Jack Triest, Roberto Grilli and Jerome Chappellaz from IGE at University of Grenoble Alpes in France, to examine the continental slope west of Svalbard aboard the R/V Helmer Hanssen. This wasn’t just any research cruise; they were testing out a new fast-response underwater membrane-inlet laser spectrometer sensor capable of revealing decametre-scale (10-meter) changes in methane concentrations over a 400 m deep methane seepage site.
Former misconceptions addressed
Standard measurements of the past did not allow for such specific results, so there were some inaccurate assumptions made about methane seep areas. One of these was that the concentration of methane throughout a seep was uniform, making it unnecessary to take multiple samples at various depths.
Thanks to the information obtained by Jansson et al. using the new spectrometer, we now know that methane concentrations can vary wildly across very short distances in seep zones, and many samples must be taken in order to get a complete picture of methane seepage activity.
New findings supported by further testing
The acquired measurements proved to be repeatable, and were reconstructed with a new numerical model for bubble dissolution. They were also confirmed through discrete sampling and acoustic surveys. Such technology can provide better insights into the processes that influence methane distribution, potentially affecting our oceans and climate, and may also be able to detect gas leaks for the fossil fuel industry.
For a full account of the study, see Jansson et al.’s article in Ocean Science entitled, ‘High-resolution underwater laser spectrometer sensing provides new insights into methane distribution at an Arctic seepage site.’
Recommended reading: Grilli, R. et al. Sub-Ocean: Subsea Dissolved Methane Measurements Using an Embedded Laser Spectrometer Technology