A Buoy Sensor Technology for Long-term Submerged Observation of the Marine Carbon Dioxide System and Isotopic Composition
The marine CO2 (carbonate or inorganic carbon) system, represented by four primary parameters – partial pressure of CO2 (pCO2) or CO2 fugacity (fCO2), total dissolved inorganic carbon (DIC or TCO2), pH, and total alkalinity (AT), is central to the marine carbon cycle, which plays a critical role in regulating the world’s oceans as CO2 sinks or sources to the atmospheric reservoir. Study of this system is critical to understanding its dynamics. In addition, investigation of δ13C variability in the world’s oceans can provide valuable insight as to the provenance, magnitude, transport and eventual fate of CO2 inputs.
The aim of the project is to develop and deploy a buoy-based technology for long-term measurement of the seawater CO2 system (pH and total inorganic carbon or DIC) and inorganic carbon isotopic composition in subsurface marine environments. We focus our in-situ sensor development to achieve high-frequency, concurrent measurement with sufficient long-term accuracy for use in climate studies. The pH and DIC measurements will be based on spectrophotometric principles using pH sensitive indicators, and carbon isotopic measurements will be made by underwater isotope ratio mass spectrometry (IRMS). Our design strategy involves use of low power components and minimization of reagent volumes. Measurement will be achieved without sacrificing sensitivity available with the existing instruments. This integrated sensor package will also provide connectivity to various commercially available peripheral sensors, including an in-situ O2 optode and CTD.
Simultaneous measurement of pH and DIC allow the seawater CO2 system to be fully characterized via thermodynamic calculation with minimal error. Integration of this bulk CO2 measurement with δ13C CO2 isotopic analysis is not only a fundamental advancement in in-situ chemical sensing technology, but will also provide a means of obtaining valuable information such as origin, distribution, dynamics, biogeochemical role, and eventual fate of CO2 within marine ecosystems. This technology is well aligned with the implementation goals of the on-going Ocean Observatories Initiative (OOI).