Development of a Modular Deep Sea In situ Dissolved Gas Extractor System

Anna Michel, Applied Ocean Physics & Engineering
Scott Wankel, Marine Chemistry & Geochemistry


2013 DOEI Funded Project


The role of the deep ocean in global biogeochemical cycles remains grossly under characterized. For example, while it is evident that strong feedbacks exist between oceanic dissolved inorganic carbon (DIC) and atmospheric CO2 and that human activities have led to dramatic increases in CO2, oceanic acidification and global modification of the carbon cycle, both the impact upon and the role of deep ocean environments in this dynamic remains virtually unknown. To begin adequately characterizing fundamental biogeochemical processes in a spatially and temporally meaningful context, robust and high-resolution chemical and isotopic data from the deep ocean using in situ measurements are required. Challenges associated with sample collection, costs associated with ships and submersible operations, and the limited information available from discrete sampling all factor into an increased need to develop robust, autonomous analyzer platforms for application to questions of deep sea biogeochemistry. The long-term monitoring and measurement of such deep-ocean biogeochemical processes will be a centerpiece of our understanding of this environment and will only be possible by the development of new in situ chemical sensors capable of reliable, high-precision, long-lifetime measurements in the deep sea environments.

Recent advances in the sensitivity and robustness of oceanographic sensors, including in situ mass spectrometers and in situ laser-based spectrometers, provide the ability to measure concentrations (and very recently isotopic composition) of a wide range of dissolved gas species. However, these sensors require the extraction of dissolved gases from fluids for analysis in the gas phase, which can hinder precision and accuracy of the sensors due to limitations in the gas extraction process. In this project, we will develop a Modular Membrane Inlet-based Dissolved Gas Extractor (MIDGE) for enhanced gas extraction that will have applicability to numerous in situ deep-sea instruments. Through modifications to the membrane inlet design, including inlet temperature control and the addition of a gas dryer and cryo-trap, we aim to increase the dissolved gas extraction efficiency and to reduce the interference from the presence of water vapor. Through these advances, we aim to significantly improve a currently viable membrane inlet that is designed to remove dissolved gases from fluids for gas phase analysis, with the ultimate goal of enhancing sensor performance. In addition, in an effort to advance instrumentation for carbon cycle studies, the MIDGE will also include an in-line sample acidification system that will enable dissolved gas species capable of CO2 measurements to quantify DIC. Demonstration of the MIDGE will be made in the laboratory and during field tests with the R/V Tioga using an in situ quadrupole mass spectrometer.