A Seafloor Shaped by Gas
Off the eastern coast of Borneo, the seabed of the Makassar Strait is an area of mounds and pockmarks. This is the Berau Delta, a region where geologic structures known as mud volcanoes and cold seeps release a steady flow of methane gas from deep within the Earth. These are not volcanoes in the traditional sense; they do not erupt molten lava. Instead, These features carry over-pressured fluids, mud, and gas that have been forced upward through fractures in the rock. The gas erupting is primarily methane.
The mud volcanoes are situated within the Kutai Basin, Indonesia's largest and deepest basin of Tertiary age (from 66 million to 2.58 million years ago). This basin contains sedimentary rock layers up to 15 kilometers thick. Tectonic compression has created a network of faults and anticlines, upward-arching rock folds, across the basin. These geological structures are pathways for gas and fluids trapped in deep, over-pressured shale formations to escape to the seafloor. The source material for the seeps originates miles underground, driven to the surface by immense pressure.
Blueprints for Life Without Sun
The constant release of methane and hydrogen sulfide from the Berau Delta seeps fuels entire ecosystems that are independent of sunlight. The base of the food web here relies on chemosynthesis. Specialized microbes, including bacteria and archaea, consume the chemical compounds in the seeping fluids to produce energy. These microbes often form thick, visible mats on the seafloor around the vents.
This microbial life supports a diverse range of larger organisms. The communities discovered at similar cold seeps include dense collections of tubeworms, clams, and mussels. These animals have symbiotic relationships with chemosynthetic bacteria that live inside their tissues. The bacteria produce nourishment for their hosts, allowing large and complex lifeforms to thrive in the complete darkness of the deep sea. The process is so effective that the biomass around cold seeps can be 10,000 to 100,000 times greater than on the surrounding seafloor.