Exploration of underwater methane sources with Transpector CPM from INFICON

Enormous amounts of methane are trapped in the ocean floor worldwide. The Alfred Wegener Institute (AWI) Helmholtz centre for polar and marine research uses an underwater mass spectrometer (UWMS) — the Transpector Compact Process Monitor (CPM) from INFICON — to investigate methane sources. With its measurement accuracy and speed, the system, from a supplier of measurement and sensor technology, makes a contribution to data stability and user-friendliness.

Methane is a harmful greenhouse gas (GHG). Due to tipping point effects, such as the decomposition of gas hydrates in oceans, it is increasingly released into the atmosphere. In aquatic systems for example, methane can reach the surface through cracks in the sediments. Another submarine source of methane is the microbial decomposition of organic material in lower sediment layers. As a result of climate change, the marine sediments are warming and releasing the GHG. The question is: how much methane is released into the atmosphere and accelerates global warming?

Localise methane leaks

The in-situ use of an underwater mass spectrometer is suitable for localising submarine sources. The main advantages are the short response time at elevated concentrations and the up to 750 times higher measurement rate of dissolved gas concentrations compared to other methods. The higher the data density, the more accurate the mapping of methane sources.

Underwater mass spectrometer shortly before deployment on the deck of the Polarstern (Image: INFICON)

The UWMS consists of a membrane inlet system for sampling and a sensor unit in which the water-soluble gases and light hydrocarbons are measured. The core of the sensor is a mass spectrometer. The AWI Helmholtz centre for polar and marine research relies on the Transpector CPM from INFICON for its research.  

Expedition in the South Atlantic

In December 2022 the research vessel Polarstern explored methane sources in the South Atlantic using an underwater mass spectrometer. On board was scientist Dr Torben Gentz who has been involved in the UWMS project in the marine geochemistry department at the AWI since 2005. Today’s system has little to do with the original device. For example, the control system and the vacuum pumps are new. “But the only remaining component is the Transpector CPM from INFICON,” said Dr Gentz.

Dr Torben Gentz, scientific lab manager in the marine geochemistry department at the AWI

According to Dr Gentz, the proportion of methane that reaches the atmosphere is crucial for research. The denser the outgassing points on the water surface and the less the water column above them is layered with different water masses, the more methane penetrates to the surface. The collection and processing of the data is fundamental, as it feeds into the assessment report of the Intergovernmental Panel on Climate Change (IPCC). Reliable measurement methods are needed to determine the role of the oceans in the global climate system.

“However, research into methane sources is not the only application,” added INFICON service manager Steffen Tippmann. Transpector CPM systems are used in semiconductor production, in the semiconductor sector for process monitoring and control as well as for contamination monitoring. However, CPM systems are also used in research, chemistry, material analysis and physics. It can be used to ionise directly at process vacuum or at a much higher pressure than with an open ion source. A differential pump system, as installed in the CPM, is a prerequisite. This can be supplemented by a variable, switchable inlet system which can be used to cover a wide analysis pressure range from atmosphere to high vacuum.

Closed ion source

Special applications such as in the AWI also take advantage of the closed ion source. Here, the process gas is ionised at a higher pressure than with an open ion source. A higher ion yield is achieved, a higher number of charged particles, which can be separated in the quadrupole according to their mass-to-charge ratio and displayed. “The result is a much more precise and detailed statement for further processing in research or process control,” said Tippmann.