Fluorescence Lifetime In situ Carbon Dioxide Sensors for Oceanic Flux and Acidification Studies at High Spatial and Temporal Resolution

This project will investigate high performance sensors for making high quality measurements of carbon dioxide (CO2) concentrations in both ocean waters and the atmosphere close to the ocean surface. This technology could equally be used in other applications including freshwater studies. The sensor technology is based on an indicator material that changes its optical properties in the presence of CO2. Specifically the indicator is fluorescent (i.e. when exposed to a high frequency light it emits lower frequency light). This fluorescence persists for a short time after the high frequency light is turned off. The length of time that the fluorescence persists (the fluorescence lifetime) changes with the concentration of CO2. Fluorescence techniques are particularly well suited to low level and high performance measurement. Currently such indicators have not been evaluated for use in the surface ocean, and can suffer from long-term drift. To combat this the proposed research will investigate novel techniques for the optical measurement used to measure fluorescence lifetime (that reduce bleaching of the indicator), will investigate novel methods of accounting for sensor drift even when operated remotely, and will comprehensively evaluate this new technology for this new application. This is the first step towards the creation of robust and low cost in situ CO2 sensing technology suitable for widespread use in this application. Carbon dioxide (CO2) is the main cause of global warming and also dissolves in seawater, increasing the acidity of the oceans which can have further negative consequence on marine life and the environment. The accurate determination of CO2 concentration in a number of locations and with short intervals between measurements, particularly in the surface ocean and lower oceanic atmosphere, is critical for assessing the response of the oceans to increasing atmospheric CO2 concentrations. Crucially data from immediately above and below the air-sea interface is of critical scientific interest particularly for predicting how much CO2 is absorbed or emitted by the oceans. Current measurement techniques using ship based systems or large complex submersible systems are too expensive and bulky to enable widespread repeated measurements. This requires accuracy of one part CO2 in ten million parts air (in air) and a similar performance for measurement of dissolved CO2 in water. We propose to evaluate the technology in conditions representative of common ocean going vehicles such as floats, profiling floats (i.e. periodically sinking to depth and then surfacing), and using opportunistic deployments on commercial ships (e.g. by analysing engine coolant water on ferries and cargo vessels). This includes measurements in the atmosphere where wash-over and spray are common, and in water whilst subject to vibration and large pressure changes. The potential commercial value of this research will be explored with Chelsea Technologies Group (a UK company).