Until now, scientists believed the main source of biomass on the seafloor was the organic matter, as dead fish and plankton, that floated down towards the depths. However, now scientists from the Heriot-Watt University in Edinburgh discovered that bacteria in the deepest parts of the seafloor are absorbing CO2 and could be turning themselves into an additional food source for other deep-sea life. Bacteria living 4000m below the ocean surface in the Clarion-Clipperton Fracture Zone (CCFZ) are consuming carbon dioxide and turning it into biomass.
We have recently made two major findings. In contrast to similar studies in the north Atlantic Ocean, we found that bacteria and not seafloor animals were the most important organisms consuming organic detritus that floats down towards the ocean floor. We also discovered that benthic bacteria are taking up large amounts of carbon dioxide and assimilating it into their biomass through an unknown process. This was completely unexpected,
…explained Prof. Andrew K. Sweetman from the Lyell Centre for Earth and Marine Science and Technology at Heriot-Watt University.
Then their biomass potentially becomes a food source for other animals in the deep sea, creating basically a potential alternative food source in the deepest parts of the ocean, where researchers thought there was none, he added.
If we upscale our results to the global ocean, our findings reveal that 200 million tonnes of CO2 could be fixed into biomass each year by this process. This equates to approximately 10% of the CO2 that the oceans remove each year, so it’s possibly an important part of the deep-sea carbon cycle. We found the same activity at multiple study sites separated by hundreds of kilometres, so we can reasonably assume this is happening on the seabed in the eastern CCFZ and possibly across the entire CCFZ.
Additionally, as the CCFZ is a prime area of interest for future seabed mining, Dr Sweetman is calling for the International Seabed Authority to ensure contractors in this area will implement carbon cycling monitoring, as well as biodiversity and genetic studies.
Sixteen contractors from countries, including UK, Germany, France and Korea, have claimed exploration rights in this region, and have begun conducting surveys to gather baseline data on biodiversity and genetic connectivity across their claim areas.
If mining proceeds in the CCFZ, it will significantly disturb the seafloor environment…The full-scale mining proposed in the Clarion-Clipperton Fracture Zone could significantly impact benthic ecosystems for decades, perhaps even longer. Now that we have shown that novel carbon cycling processes are happening on the seafloor in this region, which may be very significant in terms of the carbon cycle, authorities should insist that hopeful mining contractors study these processes in baseline surveys, impact assessments and monitoring, so that mining-related changes in this important ecosystem process can be identified and tracked,
…said Dr Sweetman.
The findings were published in the journal Limnology and Oceanography.
