Deep Ocean Microbes Unleash Hidden Carbon-Fixing Power

Researchers at the University of California - Santa Barbara have made a groundbreaking discovery about the deep ocean's carbon-fixing engine, revealing that unexpected microbes are quietly fixing carbon in the dark depths of the ocean. According to a new study published on December 10, 2025, experiments show that heterotrophs, a type of microbe, are doing far more of the work than previously expected in fixing carbon dioxide in the deep ocean. The study, led by UCSB microbial oceanographer Alyson Santoro, challenges long-held ideas about how carbon dioxide is "fixed" in the sunless depths of the ocean. While ammonia-oxidizing archaea were thought to dominate carbon fixation in the deep ocean, the research reveals that heterotrophs are playing a more significant role than anticipated. This discovery reshapes our understanding of how carbon moves through the deep ocean and stabilizes Earth's climate. "We were surprised to find that heterotrophs were fixing carbon at a rate that was significantly higher than we had anticipated," Santoro said in an interview. "This changes our understanding of the deep ocean's carbon cycle and has important implications for our understanding of how the ocean stores carbon." The research team used a combination of laboratory experiments and field observations to study the microbial communities in the deep ocean. They found that heterotrophs, which obtain energy by breaking down organic matter, were able to fix carbon at a rate that was comparable to that of ammonia-oxidizing archaea. This challenges the long-held assumption that ammonia-oxidizing archaea were the primary drivers of carbon fixation in the deep ocean. The discovery has significant implications for our understanding of the deep ocean's carbon cycle and how it affects the Earth's climate. The ocean plays a critical role in storing carbon dioxide, and understanding how it does so is essential for predicting the impacts of climate change. "This study highlights the importance of heterotrophs in the deep ocean's carbon cycle and suggests that they may play a more significant role than previously thought," said Dr. Maria Rodriguez, a marine biologist at the University of California - Los Angeles. "Further research is needed to fully understand the implications of this discovery and how it affects our understanding of the ocean's role in the global carbon cycle." The study's findings have sparked interest in the scientific community and have raised questions about the role of heterotrophs in the deep ocean's carbon cycle. Further research is needed to fully understand the implications of this discovery and how it affects our understanding of the ocean's role in the global carbon cycle. In the meantime, the research team is continuing to study the microbial communities in the deep ocean and is working to better understand the mechanisms behind carbon fixation in these environments. Their findings have the potential to significantly impact our understanding of the ocean's role in the global carbon cycle and may have important implications for climate change mitigation efforts.