高周波超音波を用いた海底堆積物中の可視化技術

抄録

The deep sea is the largest habitat on Earth for a diverse range of benthic organisms. Deep-sea organisms play important roles in the formation of sedimentary structures, the rearrangement of organic matter, pore water chemistry, and biogeochemical cycles. However, visualization and quantification of benthic organisms inhabiting the deep-sea floor has been difficult due to the sparse distribution of benthic organisms and the inability of deep-sea cameras to visualize benthic organisms living below the sediment surface. Here, a newly developed acoustic coring system (A-core-2000) was applied to visualize and detect burrowing bivalves in deep-sea sediments. In situ acoustic observations focused on patches of juvenile bivalves with a completely invertebrate lifestyle in a dense bivalve colony in a hydrocarbon upwelling area in Sagami Bay; strong backscatter from the top and bottom edges of the animals was clearly observed in the 3D acoustic data. At least 17 reflection points were identified in the study area, which were interpreted to correspond to live clams. The estimated depth of the lower margin of the clams ranged from 41–98 mm. The acoustic system presented here is useful for detecting and monitoring endogenous organisms with calcified exoskeletons. This new tool will help to better assess and understand the distribution and biogeochemical cycles of deep-sea endotherms, especially groups with hard exoskeletons.