"Particle Radio-sensor": Development of in situ particulate radioactivity sensor

Carbon fixation by marine autotrophs represents a significant (~26%) sink of the carbon released to the atmosphere from the cement industry and burning of fossil fuels. Inorganic carbon (CO2) is assimilated into biological material via photosynthetic uptake by plankton. This biological material flocculates and sinks, and is either remineralised within the ocean mixed layer or exported to deeper layers of the ocean for long term sequestration (the 'biological carbon pump'). Understanding how much of this particulate material is transferred to the deep ocean is important in quantifying the role the oceans will play in ameliorating anthropogenic atmospheric emissions of CO2, and hence climate change. These particulate export fluxes can be quantified using a number of approaches including radiochemical tracers and sediment trapping. Of the radiochemical techniques available, the use of 234Th is the most commonly applied. The 234Th readily adheres to particles, and combined with its short half-life (24.1 days) make it an ideal tracer of particles sinking through the ocean column. Traditionally, large volume (owing to the low particulate 234Th activities typically found in the oceans) in situ pumps are employed to collect particles making this method very labour intensive, and also requiring long periods of static ship during filtration periods. This leads to gross under-sampling in the oceans of this variable, leading to inconsistencies reported for the magnitude of the biological carbon pump. In situ sensors such as those used on Argo floats and gliders have been transformative for marine physics and chemistry, but analogous particulate sensors and samplers do not exist. This technology proposal seeks to address this data gap by taking the concept of an in situ particulate flux instrument to TRL 4. This will be achieved by developing an in situ filtration system and coupling this with a novel deployable beta detection module to measure particulate 234Th activity. This will provide the foundations for further work to raise the TRL of this device and to apply the innovative technology principles to other oceanic variables (i.e. dissolved phase radionuclides; other radionuclides). The ability to easily sample open ocean fluxes using autonomous vehicles at high spatial and temporal resolution would constitute a step-change in our ability to measure carbon export in a changing ocean (deoxygenation, acidification) and help scientists assess the long term effect of increasing atmospheric CO2 concentration.

Major societal and economic challenges we are addressing include resource management, management of natural and anthropogenic environmental hazards (e.g. climate change, unauthorised or accidental discharges from nuclear installations) and effects of environmental change. The ability to trace biological, chemical and physical processes using radionuclides is important in understanding on-going environmental change resulting from climate change. The added advantage of the proposed sensor is that it has cross-disciplinary applications, such as monitoring and tracing discharges from nuclear installations (eventually leading to an improved understanding of the pathways and sinks of many radionuclides). Understanding baseline processes (in this case contributing to the knowledge pool of the oceans ability to act as a CO2 sink) prior to change helps place a socioeconomic price on an ecosystem function.
A more complete understanding of the oceans role in sequestering CO2 and transporting particulates (and radioactivity) will aid policy makers in setting global CO2 emission targets, defining nuclear discharge exemption limits and placing a value on marine ecosystems. Ensuring a healthy marine ecosystem will ensure a fully functioning and efficient biological carbon pump. Economists have begun placing a value on ecosystem services, or 'giving nature a price-tag', through for instance the MAES [1] EU project, and the US Ecosystem Valuation [2]. Additional work is underway to value the marine biological carbon pump [3], with estimates of 0.1 to 1.5 trillion Euros/year for carbon sequestration services in the Mediterranean Sea alone. Global estimates would be more difficult to make without a fuller seasonal understanding of these processes across global oceans. In addition to climate change amelioration, the oceans contribute to job creation, tourism, industry, water and food security and natural resources.
The continual development of biogeochemical sensors is necessary to access new environments and determinands. Conservationists, policymakers and environmental protection groups can use data generated by these new generations of high resolution sensors for:
(a) prediction of future impacts of new and proposed anthropogenic activities;
(b) climate change related hazards prediction and amelioration efforts;
(c) aiding the economic value of the biological carbon pump (i.e. global marine ecosystem health);
(d) responsible stewardship of the natural environment for future generations;
(e) sustainable use of natural resources.
Other socioeconomic benefits to new technology development such as this include enhancing the relationship with commercial partners and end users (this includes scientists, policymakers, recreational, industrial). This project will look to develop long term relationships with all beneficiaries of the research which will help to diversify future collaborations, and add value to the products (e.g. sensors, data, knowledge exchange and transfer) generated through this research.

[1] Mapping and assessment of ecosystems and their services: http://biodiversity.europa.eu/maes
[2] http://www.ecosystemvaluation.org/default.htm
[3] Melaku Canu, D., et al., Estimating the value of carbon sequestration ecosystem services in the Mediterranean Sea: An ecological economics approach. Global Environmental Change, 2015. 32: p. 87-95.