Volcanic degassing is the main pathway of carbon release from the Earth's interior to the atmosphere. In order to constrain Earth's deep carbon cycle, there is a crucial need to quantify the relative contribution from various sources of volcanic origin. Quantitative knowledge of the isotopic composition of outgassed CO2, and specifically 12CO2/13CO2 ratio, contributes to identify carbon sources and therefore to validate degassing models. Identifying, quantifying and understanding carbon fluxes of volcanic origin through isotopic analysis aligns well with the overarching aim of the Deep Carbon Observatory's (DCO) Reservoirs and Fluxes community.
One important enabler to achieve these scientific goals relates to the development of technologies and instrumentation delivering data at relevant cost, temporal, and spatial scales. Within this framework, we developed a novel concept of real-time monitoring of carbon isotope ratio enabling compact, rugged and portable deployment. High resolution middle infrared (2-20 µm) laser spectroscopy is used to precisely fingerprint isotopologues, which owing to their slight mass difference, vibrate with different frequencies that can be resolved by lasers. The advantages of this approach include precision, non-contact measurements, large immunity to interferences, limited sample preparation, real time measurements in a compact format, and possibility for absolute concentration measurements.
The project consists of evolving a laboratory demonstrator into a field deployable instrument and conducts a first sortie to a volcanic field (La Solfatara, Campi Flegrei). To this end, the instrument was shrunk and ruggedized, without loss of sensitivity. Dedicated field electronics was also designed to allow operation using portable power sources. Lastly, a specific gas handling system was designed and implemented to sustain the chemical mixture expected from the Solfatara's fumaroles.
After the instrument preparation, the Laser Isotope Ratio-meter was deployed for one week to the Solfatara, in collaboration with Stephano Caliro from the Italian INGV, Naples. During the campaign all aspect of the system were tested in real conditions and were found to be operating very well, in a very stable fashion. A series of isotopic measurements were made using different sampling approaches, whilst Stephano Caliro was simultaneously taking samples in the usual way for subsequent isotope mass spectrometry analysis. All data are currently being scrutinized, but the instrument deployment was a great success as it operated and collected data smoothly for an entire week.
The campaign, supported and funded by the Sloane Foundation Deep Carbon Observatory (DCO), has allowed a clear validation of the LIR instrument concept in the field. We are currently working to improve the instrument based on the experience gathered and hope to participate in additional deployment campaigns in the near future. In the long term, we are working on ultra-miniaturization of the system using integrated optics technologies, in order to develop unattended, autonomous, miniature LIR that produce high-quality, real time, streaming data on the isotopic composition of CO2, with the objective to have several sites instrumented with such a system.
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