Sediment recycles the key nutrient phosphorus (P) to support marine productivity. In contrast to coastal marine environments where the sediment P recycling is largely controlled by iron (Fe) geochemistry, effluxes of bioavailable P (i.e., soluble reactive phosphorus, SRP) from low-Fe deep-sea sediments are considered decoupled from the Fe cycle and mostly driven by decomposition of organic matter. At methane (CH₄)-rich cold seeps in the South China Sea, however, we observed a strong coupling of Fe and P cycling similar to that in Fe and organic-rich coastal sediments. Higher P effluxes were found in high-CH₄ seep sediments, where Fe reduction occurred at the surface. Unlike coastal sediments where heterotrophic Fe reduction relies on the availability of reactive organic matter, at the CH₄ seeps, Fe reduction is coupled to the anaerobic oxidation of methane (AOM), a process independent of the organic matter supply. Our finding suggests the importance of chemoautotrophy in driving the benthic nutrient cycling and fluxes in the deep-sea cold seeps.

Primary Presenter: Yuxuan Lin, The Hong Kong University of Science and Technology (yuxuan.lin@connect.ust.hk)

Authors:

Jing Sun, The Hong Kong University of of Science and Technology  (jsunbk@connect.ust.hk)

Jiying Li, The Hong Kong University of Science and Technology  (jiyingli@ust.hk)