A novel membrane inlet-infrared gas analysis (MI-IRGA) system for monitoring of seawater carbonate system

Increased atmospheric CO₂ concentrations are driving changes in ocean chemistry at unprecedented rates resulting in ocean acidification, which is predicted to impact the functioning of marine biota, in particular of marine calcifiers. However, the precise understanding of such impacts relies on an analytical system that determines the mechanisms and impact of elevated pCO₂ on the physiology of organisms at scales from species to entire communities. Recent work has highlighted the need within experiments to control all aspects of the carbonate system to resolve the role of different inorganic carbon species on the physiological responses observed across taxa in real-time. Presently however, there are limited options available for continuous quantification of physiological responses, coupled with real-time calculation of the seawater carbonate chemistry system within microcosm environments. Here, we describe and characterise the performance of a novel pCO₂ membrane equilibrium system (the Membrane Inlet Infra-Red Gas Analyser, MI-IRGA) integrated with a continuous pH and oxygen monitoring platform. The system can detect changes in the seawater carbonate chemistry and determine organism physiological responses, while providing the user with real-time control over the microcosm system. We evaluate the systems control, response time and associated error, and demonstrate the flexibility of the system to operate under field conditions and within a laboratory. We use the system to measure physiological parameters (photosynthesis and respiration) for the corals Pocillipora damicornis and Porites cylindrica; in doing so we present a novel dataset examining the interactive role of temperature, light and pCO₂ on the physiology of P. cylindrica.