Carbon dioxide emitted from hydrothermal vents, as an important part of the global carbon cycle, can directly affect hydrothermal ecosystems. However, traditional chemical analysis methods cannot directly measure the concentrations of dissolved CO₂ in high - temperature hydrothermal fluids. 

A research team led by Prof. YAN Jun and Prof. LI Chaolun from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) made progress in in-situ Raman spectroscopy quantitative detection of deep-ocean hydrothermal fluid system.

With the homemade Raman insertion probe (RiP), they conducted the in-situ quantitative Raman spectroscopy detection of high-temperature hydrothermal fluids in the hydrothermal field in the middle Okinawa Trough.

They obtained the in-situ concentrations of dissolved CO₂ and SO₄^2- in the high-temperature hydrothermal vent fluids for the first time in the world. Their findings were published in Geochemistry, Geophysics, Geosystems.

As a major discovery of earth science in 20th century, the deep-ocean hydrothermal fluid system achieves the matter and energy exchanges between different circles.

By means of research vessel (RV) Kexue and Remotely Operated Vehicle (ROV) Faxian, the RiP has detected lots high-temperature hydrothermal vent fluids in the hydrothermal fields in the Manus and the Okinawa Trough since 2015 and collected a number of in-situ Raman spectra.

According to the research, the content of SO₄^2- as seawater mixing index in measured high-temperature hydrothermal fluids was nearly zero. It proved that the hydrothermal fluids sampled by the RiP contained no seawater, that is to say, the measured sample could be seemed as the primitive hydrothermal vent fluids.

By comparing the CO₂-concentration in the same hydrothermal vent measured by ROV with gas-tight sampling, the researchers found that the concentration determined by in-situ measurement was three times higher than that by gas-tight sampling in laboratory.

The researchers found that the influences of hydrothermal fluids on global carbon cycle and climate change might be much greater than people thought. Their findings are of great significance in promoting the in-situ spectroscopy detection in extreme deep ocean environment, and may help people re-understand the influences of hydrothermal fluids on global oceans.

The research was funded by the National Natural Science Foundation of China, the Ocean Pilot Project of the Chinese Academy of Sciences, and the Frontier Science Key Programs of Chinese Academy of Sciences.