About this Research Topic
The Hadal zone refers to the deepest areas of the ocean between 6,000 m and approximately 11,000 m. It represents 1–2% of the global benthic area but constitutes the deepest 45% of the vertical depth gradient of the ocean. Hadal areas are almost exclusively comprised of oceanic trenches that are formed by plate subduction. They are part of the least investigated biosphere on Earth due to the great challenge of sampling in those areas.
Microorganisms are the dominant living creatures in the deep ocean (including the Hadal zone) and are of great scientific interest because of their important role in global carbon cycle. Fixed carbon in the form of organic matter from the surface euphotic zone and from re-suspended and laterally transported sediments provides the major food source feeding the living organisms in the deepest ocean. Magnificent progresses have been made recently in Hadal microbiological research owing to the advancement in sampling technologies in genomics tools, which reveal trench-specific planktonic organisms having unique metabolic capabilities. Also surprising is the elevated respiration rates measured in trench sediments compared to those in nearby mesopelagic sediment, suggesting enhanced microbial activity in the former. Niche specificity in microbial assemblies involved in nitrification also suggests the uniqueness of trench environment. These results have profound implications for a holistic view of the global deep ocean biosphere. Further research is needed to consider trenches as an integral component of the ocean biogeochemical processes. Specifically, questions will need to focus on 1) the origin and fate of organic and inorganic carbon in trenches, 2) the common features of the microbiome shared by trenches globally, 3) the unique characteristics of each individual trench in comparison with the open ocean, and 4) coupling between carbon cycle and other elements driven by trench organisms.
The proposed Research Topic on Hadal microbial biosphere aims to report the latest progresses in understanding the biogeochemistry and corresponding microbial ecology and evolution in this least explored environment. Manuscripts to be included in this Research Topic will contain reviews on Hadal biosphere, designs of field infrastructure and sampling technologies necessary to address grand scientific questions unique to the Hadal environment, and research papers on the diversity, ecological function, biogeochemical consequences and evolution of Hadal microorganisms, and ecological linkage between Hadal biosphere and the adjacent environment
Keywords: Microbiology, environmental genomics, global carbon cycle, trenches, deep ocean biosphere
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