Our latest research has discovered some very important things about the large carbon stocks that are buried deep within marine sediments. An international team of scientists, co-led by Professor Wang Faming from the South China Botanical Garden of the Chinese Academy of Sciences, has explored how heat can activate ancient carbon, transforming it into a vital food source for microbial life that thrives in extreme environments deep beneath the ocean’s surface.
Marine sediments hold a whopping 15 million Gt of carbon. This huge energy flux supports large, diverse, subsurface ecosystems, often called the “deep biosphere.” This innovative study exposes the ability of increased temperature to awaken previously dormant carbon sources in sediments. As such, it fundamentally reorients our scientific comprehension of extreme life and Earth’s deep carbon cycle.
The Significance of Marine Sediments
Marine sediments represent Earth’s largest carbon reservoir, located approximately 1.2 kilometers below the ocean’s surface. Over geologic time scales, organic matter has accumulated within these sediments. This build up provides an important reservoir of carbon that supports all forms of microbial life. As such, the whole oceanic water column sequesters roughly 39,000 Gt of carbon. Yet, behind that, it’s marine sediments in the lead with a staggering 15 million Gt.
Researchers wanted to know more about how this carbon pool sustains life. They examined sediment samples that had been collected from the Shikoku Basin in the northwestern Pacific Ocean. Most importantly, these samples are definitely 7.8 million years old and have been through several heating cycles. Their findings reveal that more than half of the volume of marine sediment globally heats up to above 40 °C. This higher temperature fosters important biochemical reactions that underlie dynamic microbial communities.
Temperature’s Role in Carbon Reactivation
Their research shows that once marine sediments are heated to around 85 °C, carbon-reactivation processes become dramatically faster. Under these harsh conditions, relatively uncomplicated molecules are created. These compounds release nutrients that fuel microbial communities that thrive well below the surface of sediments. This finding is important because it shows how heat can “wake up” old carbon, making it available for microbial communities to metabolize.
Further, marine sediments undergo a reversal of the marine carbonate mineral carbon pump once temperatures exceed 35 °C. This process, known as photosynthesis, is ocean’s carbon cycle’s foundation. This phenomenon changes the balance of carbon cycling in these ecosystems. At temperatures > 55 °C microbial carbon pump starts to reverse. This change has a big impact on how microbes break down organic material, affecting how we think about organic material’s long-term carbon implications.
In fact, only around 0.25% of the organic carbon found in marine sediments ever becomes bioavailable. The comparatively enormous size of this reservoir renders it an important landscape- and climate-determining energy source for microbial life. The implications are huge. Even small increases in temperature can enhance microbial activity and carbon cycling in deep-sea ecosystems.
Implications for Scientific Understanding
Taken together, the findings from this study are wide-reaching and crucial for helping to understand how temperature impacts the role that marine sediments play in cycling carbon. What previous research has demonstrated is that heat can reactivate these dormant carbon reserves. This exciting finding paves the way for future work to explore how these subsurface ecosystems contribute to global biogeochemical cycles.
More than a climate study, the report’s revelations further underscore marine sediments’ value to larger climate conversations. As temperatures increase due to climate change, it’s important to know how sediments will respond. Such knowledge would offer critical insight into the carbon release and storage dynamic.