In situ characterization of naturally occurring methane and ethane at sites of active serpentinization by tunable diode laser spectroscopy

Abstract

We describe recent field and lab. measurements of methane and ethane gases from two sites of active serpentinization: The Cedars in Northern California, and Cabeco de Vide in Central Portugal. Tunable diode laser spectroscopy is discussed as a means for identifying and rapidly quantifying fluxes of light hydrocarbons, and for understanding their mechanisms of prodn. The Carbon Isotope Laser Spectrometer (CILS), developed at the Jet Propulsion Lab. provides ppm or better sensitivity to both methane and ethane, with a thousand-fold greater sensitivity to the latter, appropriate to its lower abundance in Earth's atm. We describe methods for sampling these gases from naturally exsolved gases, and directly from fluids.