WP2 Autonomous sensors, analysers and microsystem technology for chemical monitoring
Lead: Dr Nadine LeBris. Ifremer, France.

Sensors and analysers based on wet chemistry and electrochemistry techniques exist for a limited number of key-parameters of marine environments (e.g. NO₃^-, PO₄^3-, Fe, Mn, Si, CO^₂, O^₂, pH). Prototypes of these systems have been widely used in situ for short-term deployments in various marine systems.^(1,2) These first generation instruments are, however, physically large and power consuming, constraining their adaptation for autonomous use and deployment on a wide range of platforms. The integration and reduction of energy requirement achieved with newly developed instruments, such as the autonomous CHEMINI flow-analysers and the SPOT and SPHT voltametric and potentiometric probes allow a new step toward long-term in situ measurement. Analytical methods and transduction devices still have to be optimised and validated for the measurement environmentally important species such as reduced sulphur compounds, pH and carbonate ions with a suitable sensitivity and stability over time. Within this WP existing sensors will be improved and adapted to existing in situ platforms (sulphide, oxygen, nitrate, silicate), and new long-term sensors (pH, carbonate, phosphate) will be developed. Within this WP existing sensors will be improved and adapted to existing in situ platforms (sulphide, oxygen, nitrate, silicate), and new long-term sensors (pH, carbonate, phosphate) will be developed. Additionally, as microsystems for chemical analysis in industry develop rapidly, it appears timely to explore the possibilities for further miniaturisation of sensing and flow technologies and methods for the monitoring of several target environments.

ANAIS - Autonomous Nutrient Analyser In Situ (indicated by arrow).  Image courtesy Veronique Garcon, CNRS

Enhancing the sensitivity to determine nutrients and metals at nM levels is far from a purely academic exercise; low concentrations of iron in surface waters are known to have a major impact on primary productivity of the oceans, with associated effects on climate modification by the oceans.

The development of novel sensors for ocean pH and carbonate are important for our understanding of the interaction between the climate and marine systems, a key role of this WP will be to develop novel sensors for these parameters. Increasing carbon dioxide in the atmosphere, as a result of anthropogenic activity, has the potential for detrimental changes to the marine system as it results in an increase in the ocean’s acidity and alters the carbonate system. Ocean acidification is considered one of the greatest threats to the marine ecosystem; we presently have no in situ sensors for pH or carbonate that allow the long term, accurate determination of these variables.

Electrochemical techniques have proven to be particularly relevant for the monitoring of redox cycling in various aquatic environments and are a promising way to address the temporal dynamics of biogeochemical systems. An adaptation of electrochemical methods with particular attention to the validation of their accuracy in long-term autonomous in situ use will be performed; these will focus on the development of voltametric sensors for reduced sulphur species and their application for monitoring chemically unique environments such as hot and cold seeps and upwelling zones.

MicroSystem Technology (MST) promises to bring a revolution to in situ chemical sensing. By using design and manufacture techniques akin to those employed in the electronics industry, miniature analytical systems that are mass produced and low cost are an approaching reality. This work package will explore the concept of the development of MST modules for use in in situ sensing systems. MST components (such as mixers, detection optics, pumps etc) will be used to sequentially replace macro (traditional) components in chemical sensor systems to effect substantial miniaturisation and performance enhancement. This part of the work package will focus on the use of well-characterised wet chemistry techniques (e.g. for nitrate, phosphate, iron and manganese), although extension to other chemistries will be investigated (e.g. important trace species that are not yet studied). This element will form strong links with work on macro chemical analysers within this work package. The application of liquid core waveguide technologies for use in in situ sensor development will be explored with the aim of developing highly sensitive sensors.

(1) Le Bris, N., et al., 2000. Mar. Chem. 72, 1-15. (2) Le Bris N. et al., 2006. Mar. Chem. (98) 167-182.