Development of an oceanic in situ carbon dioxide sensor for high spatial and temporal resolution measurements

We propose to develop and trial a novel high performance fluorescence lifetime based technology for sensing of carbon dioxide (CO2) concentrations in the marine atmosphere and surface ocean. The technology promises a significant step in scientific capability in climate research, similar if not greater than that enabled by the advent of robust and accurate oxygen sensors based on fluorescence lifetime indicators. CO2 is the main vector for global warming and ocean acidification. Since the industrial revolution, ca. 30% of the global anthropogenic CO2 emissions have been taken up by the oceans. The continued ability of the oceans to act as a sink is of critical importance for future trends in atmospheric CO2, climate and ocean acidification. Crucially, CO2 data from the surface zone immediately above and below the air-sea interface, is of scientific interest for flux studies. Such studies enable estimation of current transfer rates of CO2 between the atmosphere and the oceans. There is evidence that the driving force behind the air-sea flux of CO2 is decreasing and that this is partly responsible for the acceleration of atmospheric CO2 concentration annual growth rate. The overall aim of this PhD project is to develop the next generation of marine in situ pCO2 sensors that will utilise fluorescence life-time technology, using advanced dual lifetime referenced indicators and optical interrogation techniques employing high frequency photon counting and fluorescence decay curve fitting. The sensor will use the acidic character of CO2 to determine CO2-dependent change of pH inside a commercially available (Presens GmbH) indicator material. The sensors are built from a pH sensitive fluorescence indicator, a CO2 sensitive buffer, a CO2 insensitive reference indicator and a supporting gas-permeable (but ion impermeable) membrane matrix. The objectives of the PhD project are to 1) optimise the fluorescence interrogation approach, 2) determine precision/accuracy of sensor, 3) determine temperature and salinity dependency of sensor, 4) develop temperature compensation algorithm, 5) package sensor in miniaturised housing, 6) trial the CO2 sensor on coastal/oceanic voyages. This study will provide an important contribution to UK research on marine sensor development, air-sea exchange of CO2, ocean acidification, marine biogeochemistry, and the proposed research will strengthen our international position in climate change research. The PhD student will utilise the established laboratories for Marine Microsystem technology at NOCS and the UK Ocean Acidification Carbonate Chemistry Facilities (set-up using NERC and EPSRC Capital Grants), and therefore will work in excellent analytical facilities. The PhD student will receive an excellent hands-on training in analytical chemistry, sensor development, carbonate chemistry and marine biogeochemistry, and will undertake appropriate courses in analytical chemistry and marine biogeochemistry. The Centre for Marine Microsystems at the National Oceanography Centre, Southampton [NOCS] combines skills and scientific resources from across the University of Southampton with the Natural Environment Research Council sensor section at NOCS to provide an internationally known research group working at the leading edge of marine sensor technology [see www.soton.ac.uk/rmst]. This large group with interests extending from micro fluidics and micromechanical expertise to studies on biofouling, provides an excellent environment for the training of a research student in the proposed area. Several marine in situ sensors from the group are already at technology readiness levels 4-6, and additional chemical analytical and biogeochemical skills are provided through the PI Achterberg for the proposed project. The research team will facilitate NERC funded leading technology to be developed by the PhD student to answer crucial environmental questions, in addition to key skills training.