Discovery Transforms Understanding of Hydrogen Depletion at the Seafloor

The discovery of hydrothermal vents―where volcanoes at the seafloor produce hot fluid exceeding 350 degrees Celsius or 662 degrees Fahrenheit―fundamentally changed our understanding about Earth and life in the 1970s. Yet, life at and underneath the seafloor is still very much a mystery today.  

Gaining a better understanding of these volcanically active areas is important, as the chemistry at seafloor vents impacts ocean chemistry more generally. In addition, the seafloor’s unique environment supports biological and non-biological processes that offer clues as to how life on Earth first began, how it is sustained over time―and the potential for life on other planetary bodies.

According to geochemist Jill McDermott, a professor in the Department of Earth and Environmental Sciences at Lehigh University, past studies of the chemistry of hydrothermal vent fluids have revealed reductions in certain gas species, such as molecular hydrogen. These depletions were thought to be caused by microbiological communities living in the shallow seafloor, collectively called the subseafloor biosphere.

However, results of a new study by McDermott and colleagues contradict that assumption. The researchers analyzed gas-tight hydrothermal fluid samples from the world's deepest known vent field, the Piccard hydrothermal field at the Mid-Cayman Rise, which is at a depth of 4970 meters, or about 16,000 feet below sea level. They observed chemical shifts in their samples, including a large loss of molecular hydrogen, that could only be the result of abiotic (non-biological) and thermogenic (thermal breakdown) processes, because the fluid temperatures were beyond the limits that support life―understood to be 122 degrees Celsius or around 250 degrees Fahrenheit, or lower.

Read more at Lehigh University

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