Microorganisms living deep beneath the Ross Sea are helping to capture carbon in complete darkness, according to a new study led by Italy's National Institute of Oceanography and Applied Geophysics (OGS).
When most people think about ocean carbon uptake, they picture microscopic plants near the sea surface using sunlight to convert carbon dioxide into organic matter through photosynthesis. However, the new research suggests that important carbon-fixing processes are also taking place hundreds to thousands of metres below the surface, where sunlight never penetrates.
Researchers examined seawater collected from depths between approximately 200 and 2,000 metres in the Ross Sea, one of Antarctica's most productive marine ecosystems. Their analyses showed that naturally occurring microorganisms were able to convert dissolved inorganic carbon into organic material despite the absence of light.
Unlike surface phytoplankton, these microbes are thought to obtain energy from chemical reactions rather than sunlight. This process, known as chemosynthetic carbon fixation, has been documented in other parts of the world's oceans, but its contribution to Antarctic carbon cycling has remained poorly understood.
The scientists directly measured carbon fixation rates within the sampled water masses. They then used those observations to estimate what the process might mean across a much larger area of the Ross Sea. Based on that regional extrapolation, the researchers calculated that dark carbon fixation could represent an amount equivalent to roughly 5% of the Ross Sea's annual carbon dioxide uptake.
While that figure is an estimate rather than a direct measurement of the entire Ross Sea, it points to a potentially overlooked component of the Southern Ocean carbon budget.
The findings add another layer to scientists' understanding of how Antarctica influences the global climate system. They also highlight the role of microbial communities that operate far from the surface, quietly processing carbon in one of the planet's most remote and least understood marine environments.
Source: OGS, PNRA DEEPROSSS project, CNR-IRBIM.