In situ Raman observations reveal that the gas fluxes of diffuse flow in hydrothermal systems are greatly underestimated

Reduced gases released from hydrothermal vents supply energy to local deep-marine ecosystems and play an important role in global biogeochemical cycles of sulfur and carbon. The habitable, lower-temperature diffuse flow sites in a hydrothermal system generally have higher biomass than focused flow sites. However, a scarcity of observational data of diffuse flows limits our understanding of the role of volatile gases in these environments. We deployed in situ Raman spectroscopy in the Iheya North hydrothermal field of the mid-Okinawa Trough (East China Sea). A Raman probe inserted directly into hydrothermal vent orifices with tem-peratures of 30-302 degrees C collected Raman spectra of hydrothermal fluids. In situ observation data show that the greater volume of diffuse flows results in a flux of volatile gases one to two orders of magnitude higher than that from focused flow environments. This indicates the great potential of diffuse flow for supplying energy and material to hydrothermal systems. The role played by diffuse flow should be reassessed.