In situ carbon isotope exploration of an active submarine volcano

The geologic and biogeochemical cycling of carbon in deep ocean environments has important implications for our understanding of the functioning of Earth systems across a wide range of spatial and temporal scales. To improve our ability to study the cycling and fluxes of carbon in the deep ocean, new technologies are emerging for making in situ measurements of carbon compounds over a range of environmental contexts. Within many of these deep-sea environments, fluxes of carbon compounds often occur as either venting fluids or rising gas bubbles. Key compounds of interest include methane (CH4), dissolved inorganic carbon (DIC), and carbon dioxide (CO2) – a component of DIC. In particular, measurement of the carbon isotopic composition (δ13C) of these pools can offer a better understanding of the nature of sources, fluxes, and cycling processes involving these compounds. Here we present the advancement of an in situ laser spectrometer (initially developed for measurement of δ13CCH4 only) into a sensor that can measure δ13C of both CH4 and CO2 in both deep-sea bubble plumes as well as geologic fluids. We present results of a 2014 telepresence-enabled investigation of a back arc submarine volcano (Kick’em Jenny) in the Caribbean Sea. In situ isotopic analysis of both bubbles and fluids suggest a primarily thermogenic origin for CH4 and a magmatic origin for CO2, yet highlight the occurrence of some heterogeneities indicating locally elevated contribution of organic matter to DIC fluxes.