Carbonate Chemistry Autonomous Sensor System (CarCASS)

Humans release approximately 10 petagrams of carbon per year into the atmosphere, mainly through combustion of fossil fuels, about half of which is absorbed by the ocean. As CO2 enters the ocean it dissolves to form carbonic acid (H2CO3), a weak acid which readily dissociates to bicarbonate (HCO3-) and carbonate (CO32-) ions, and H+ lowering the pH of seawater. This process, defined as Ocean Acidification, has been documented in several oceanic reservoirs through time series observations and is expected to have adverse consequences on marine life and especially marine calcifiers (crustaceans, shellfish, some plankton species, corals etc.) which form hard structures from CaCO3. Ocean acidification is expected to cost the world economy 1 trillion USD annually by 2100 through negative impacts on ecosystem services. In the UK, four of the ten most valuable marine species are calcifying shellfish or crustaceans with an annual worth around £250m. Furthermore, aquaculture of shellfish is worth annually about £30m. High spatial and temporal resolution measurements of carbonate chemistry parameters are therefore needed to concurrently characterise variability in space and time to better understand biological tolerances and societal responses to ocean acidification. Although efforts have been made to increase the availability of high resolution carbonate chemistry observations in the ocean, the lack of automated high performance low cost carbonate sensors continues to hold back continuous and spatially extensive carbonate chemistry measurements using autonomous vehicles. Developing sensors capable of fulfilling future Marine Autonomous System (MAS) deployment goals, is therefore a matter of urgency for deciphering knowledge gaps and uncertainties in our understanding of the global ocean carbon cycle and optimisation of global models of ocean acidification and its impacts. At the Ocean Technology and Engineering Group (OTEG) of the National Oceanography Centre (NOC) we develop sensors for in situ measurements of biogeochemical, physical and biological parameters in the ocean including Dissolved Inorganic Carbon (DIC), Total Alkalinity (TA) and pH. Currently these sensors are still at a relatively early developmental stage (Technology Readiness Level (TRL) 4-6). In this proposal we request funds to advance the TRL of these technologies and integrate them into a small autonomous device we call Carbonate Chemistry Autonomous Sensor System (CarCASS). The CarCASS will also incorporate an award winning fast measuring pH sensor, developed by our partners ANB Sensors, which as part of this work we will advance from TRL 6 to TRL 8. The CarCASS will be small enough for integration on most MAS including the Autosub Long Range (ALR), Kongsberg Seaglider, C-Enduro ASV, Wave Glider and Argo floats. As an integrated system, CarCASS will be the first device capable of autonomous complete characterisation of the seawater carbonate chemistry from surface to full ocean depth. Each sensor component will be fully autonomous and capable of being deployed independently. The DIC and TA sensors will be the first devices capable of autonomous measurements at full ocean depth while the pH sensors will provide for the first time fast (0.1 Hz) self-calibrated measurements autonomously anywhere in the ocean. This project will deliver tools which will enable continuous and spatially extensive carbonate chemistry measurements in the ocean deciphering knowledge gaps and uncertainties in our understanding of the global ocean carbon cycle.