Toward In-situ Measurements of the CO2 System in Deep Ocean



Oceanography has entered a new technology era where observatories and in-situ measurements are gradually taking shape to form a global observing network.  This technology revolution in oceanography will significantly improve our ability to monitor and study the ocean at an unprecedented spatial and temporal resolution.  However, there is clearly a gap between observing platforms (e.g. buoys, cabled observatories, Remotely Operated Vehicles or ROVs, and water profilers) in operation and biogeochemical in-situ sensors that can be deployed on them.  Development of these sensors is mostly lagging behind deployment of observing platforms, and the demand for sensors has been increasing in recent years.  This is especially the case for measurements of the marine CO2 system, which is represented by four primary parameters (pH, pCO2, total dissolved inorganic carbon or DIC, and total alkalinity or TAlk).  High quality measurements of the marine CO2 system with sufficient temporal and spatial coverage serve as a foundation for studying the marine carbon cycle, and predicting future global climate change and effects of ocean acidification.  However, we still largely rely on shipboard bottle sampling and discrete analyses of the four CO2 parameters to cover all depths in the ocean.  This cost-inefficient process severely limits the scope of temporal and spatial observation.  

We herein request funding to initialize development of an in-situ spectrophotometric sensor package that simultaneously measures seawater pH and DIC at full ocean depths (0 – 5000 m).  It is targeted for sub-surface deployment on ROVs and in-situ profilers. Compared to previous developments, this in-situ pH-DIC sensor package will be deployed deeper in the ocean, cover greater measurement ranges, and be able to fully characterize the seawater CO2 system with high spatial resolution.  This proposed study will result in construction of a prototype benchtop version of the pH-DIC sensor, which will then be used to establish calibrations and optimize measurement conditions for pH and DIC measurements that are suited for a wide range of temperature, salinity, pressure and concentration gradients to be encountered in sub-surface deployment.  We will also explore new sensor design and resolve technical challenges that we may face during in-situ development.  The success of this study will thus provide invaluable preliminary data and pave the way for future sensor development in this direction.

Development of the sub-surface in-situ pH-DIC sensor will enable in-situ exploration of the CO2 system near deep ocean phenomena, such as hydrothermal vents and submarine volcanoes.  Studying the CO2 system dynamics of these environments may have significant implications for the ecosystems of these life-rich habitats and the marine carbon cycle.  The developed technology will also have great potential to be deployed on ocean observatories to study carbon cycle and ocean acidification.