WP1 Optical sensor development
Lead: Prof. Antje Boetius. MPI. Germany.

Optical based sensor systems show great promise for use in marine and aquatic environments, ranging from the development of in situ Raman technology, to the use of optodes for the determination of oxygen, nutrients and pH, through to hyperspectral imaging or by using specially developed sensing foils in one and two dimensions.

Significant progress has been made in the application of Raman spectroscopy to the deep marine environment.^(1,2) However, the technology and its in situ application, as well as a full characterisation of elements of interest in the deep-sea is in its infancy. In addition, surface enhanced Raman spectroscopy (SERS) will yield a significant gain in sensitivity by developing specific SERS active sensor membranes for trace detection of inorganic and organic analytes amplifying the Raman signals of interest.⁽³⁾

Most chemical and biological processes result in changes in dissolved oxygen concentrations. Oxygen is therefore a prime parameter to measure in marine environmental studies. Because of technological limitations of previous sampling methods and sensors, long-term monitoring of oxygen was not possible until the introduction of accurate and stable optical oxygen sensors.⁽⁴⁾ This technology has revolutionized the possibilities to measure oxygen and has resulted in numerous new insights.^(5,6) One limitation of these sensors is however that their response is too slow to be optimal for use in profiling applications (e.g. gliders and AUVs) or to access turbulence induced sub-second oxygen variations which often occur close to the bottom or surface. Optode technology also has an advantage over conventional sensors in that it can be used to assess oxygen distributions in two dimensions using so called planar optodes. With planar optodes it is possible to obtain photos of the oxygen distribution at micrometer scale for example at the sediment water interface. For in-situ use these systems are still in their early days^(7,8) and more development is needed to optimise the absolute accuracy including the temperature compensation, the response time and to make the automatic image treatment better. If improved, an exciting new application of improved planar optodes would be to use this technology to obtain more reliable air-sea exchange coefficients, which are crucial in climate change studies.

Imaging technology is widely used in marine sciences, from satellites to ship board systems to diver operated systems in surface waters.⁽⁷⁾ The technology although in its infancy for use in the deep marine environment shows great promise for use in community structure studies. In combination with other sensors they provide us with tools to assess benthic community structure and the cycling of oxygen over the interface between the sediment and the water column.

(1) Brewer, PG, et al., 2004. D.S.R I 51(5) 739-753. (2) White et al., 2006. Mar. Chem. 99 (1-4) 12-23. (3) Schmidt, H. et al., 2004 . Mar. Poll. Bull. 49, 229–234. (4) Tengberg A. et al., (2006). Limnol. Oceanogr. Meth. 4, 7-17. (5) Körtzinger, A., et al., (2004a). J. Atmos. Ocean. Techn. 22: 302-308. (6) Körtzinger, A., et al., (2004b). Science, 306: 1337. (7) Glud, R. N., et al., 2001. Limnol. Oceanogr. 46:2073-2080. (8) Glud R.N., et al., 2005. D.S.R I, 52: 1974-1987.