Microbes Harness Ancient Carbon in Deep-Sea Vents
Researchers have discovered that microorganisms thriving in extreme hydrothermal vent systems off the coast of Taiwan are utilizing carbon dioxide that has been locked away for millennia, revealing a previously unknown pathway in the global carbon cycle. This ancient carbon, originating from the Earth’s interior, fuels life in these harsh environments and impacts the broader marine ecosystem.
The Kueishantao Hydrothermal System
A team from MARUM – Center for Marine Environmental Sciences at the University of Bremen and the National Sun Yat-Sen University, along with the Exploration and Development Research institutes in Taiwan, investigated a hydrothermal vent system at a depth of approximately ten meters off Kueishantao island. Their research, published in Communications Earth & Environment, focused on tracking the movement of carbon released from these vents and its incorporation into marine life.
Tracing Ancient Carbon with Isotopes
The study leveraged the unique properties of radiocarbon (14C) to trace the carbon’s journey. 14C is created in the upper atmosphere and enters the carbon cycle, but it decays over time. Carbon from the Earth’s interior, having been isolated for eons, is virtually devoid of 14C, making it “radiocarbon-dead.” By measuring the 14C content, researchers could distinguish between modern carbon and the ancient carbon from the vents. “Our approach was to use the old, 14C-free carbon from hydrothermal sources as a natural marker,” explains Dr. Hendrik Grotheer, a geochemist at the Alfred Wegener Institute .
A Unique Metabolic Pathway: The rTCA Cycle
Previous research by the team revealed that specialized bacteria at these vents employ a highly efficient metabolic pathway called the reductive tricarboxylic acid (rTCA) cycle. This pathway allows microorganisms to incorporate carbon dioxide into their biomass even under extreme conditions. The current study demonstrates that this ancient carbon from hydrothermal vents accounts for up to 30% of the bacteria’s biomass within the system and is transferred through the food web. Even crabs feeding on these microbes exhibit a measurable age increase due to the incorporation of this ancient carbon.
Photosynthesis and Carbon Assimilation
Researchers also investigated how the carbon was assimilated – through chemosynthesis (using chemicals for energy) or photosynthesis (using sunlight). Surprisingly, the study found evidence that photosynthesis plays a role in the uptake of this ancient carbon by organisms further from the vent. This was determined through the use of hydrogen isotopes.
Limited Retention in the Ecosystem
Despite the various assimilation mechanisms, the study found that most of the carbon released from the vents doesn’t remain within the local ecosystem. “Only a compact proportion of the total carbon released actually remains in the local ecosystem. The majority of the CO2 escapes direct biological use and is distributed into the ocean with the surrounding water masses or escapes into the atmosphere,” says Joely Maak, the study’s lead author and researcher at MARUM .
Future Research and International Collaboration
The research team plans to further investigate the release of dissolved organic carbon and micronutrients from these vents and their broader impact on ocean biogeochemistry. This work is part of the Cluster of Excellence “The Ocean Floor – Earth’s Uncharted Interface.” The study highlights the importance of international collaboration, particularly between Taiwan and Bremen, in unraveling the complexities of ocean processes. “This study shows the importance of long-term international cooperation for understanding complex oceanic processes,” says Dr. Solveig Bühring .
MARUM’s research contributes to a better understanding of the ocean’s role in the Earth system, including its influence on climate, the carbon cycle, and the creation of unique biological systems.