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Sea parameters

Chemical in situ sensors

The majority of chemical measurements in sea water are still based on water samples taken with bottles or pumps that are analysed later in the lab. With this method neither small scale processes or transient events can be resolved adequately nor can long term datasets of chemical variability be gained from long term stations or moorings. To fill these gaps chemical in situ sensors are needed that exhibit similar spatial and temporal resolution as the physical sensors (e.g. for conductivity and temperature). In the long term these chemical in situ sensors should reach the same accuracy, precision and resolution as the analysis in the lab. However, high resolution in situ measurements with reduced accuracy and precision can also give valuable hints at the involved processes and therefore guide an optimized sampling strategy.

There are various approaches in the development of new chemical sensors that can be divided into two main groups:

1. Miniaturization of wet chemical analysers
For the deployment on a variety of platforms wet chemical analysers have to be optimized for minimum power and reagent consumption. To this end small industrial fluidic components such as solenoid pumps and valves are used (e.g. in the Fe/Mn analyser) together with small volume absorption cells. A further step is the use of microfluidic MEMS components. MEMS (Micro-Electro-Mechanical Systems) are based on methods of the electronics industry, where mechanical structures are etched into silicon or other substrates and these structures are combined into microfluidic components (e.g. pumps, valves, mixers etc.). Together with microelectronics and microoptics these components can be put together into a microfluidic analyser.

2. Physical-chemical methods
Sensing mechanisms that don't need reagents are ideal for longer term deployments of chemical sensors. Examples for this kind of methods are opt(r)odes, direct optical absorption measurements and (micro)-electrodes.

One of our tasks for the development of new oceanographic chemical sensors is the search of new technologies developed in various fields, e.g. for industrial sensors. The potential of these technologies for an application for oceanographic sensors has to be evaluated with special consideration of the special demands of the underwater environment with typically low concentrations of analyte in the complex mixture that is seawater. Together with the technology leaders we are working on the adaption and modification to bring new technologies in the sea.

Dr. Ralf Prien

Process scales (after Dickey 2001)
Oceanic processes span several orders of magnitude - spatially as well as temporally (from Prien, 2007, after Dickey, 2001)
resolution comparison
Hourly measurements (lower panel) as measured by an in situ sensor, show a much better resolution of the signal dynamics than is achievable by taking water samples (upper panel). (From Prien, 2007)