GEOGRAPHY

The formation of the transformation of seabed pits into underwater waterways is revealed


Recently, the team of Li Wei, a researcher at the South China Sea Institute of Oceanology, Chinese Academy of Sciences, and a number of scientists inside and outside the United Nations conducted in-depth research on the formation mechanism of the seabed waterway in the seabed pockmark area, and revealed the specific process of the transformation of the seabed hemp pit into a seabed waterway under the action of undercurrent erosion through numerical simulation. The research paper was published in the journal Land Surface Processes and Geomorphology. Yu Kaiqi is the first author of the paper, and Li Wei is the corresponding author.

Distribution of seafloor hemp pits affected by undercurrent activity worldwide (the northwestern part of the South China Sea was used as an example in this study). Photo courtesy of the research team

In the deep-water environment of the global seabed, when the bottom flow encounters the “concave” seabed topography (such as the seabed pockmarked pit), it will often erode and modify the seabed, thereby inducing the development of the seabed. As a material transport channel and storage site in the depths of the ocean, the formation and development process of submarine waterway has important indicative significance for the research of deep-sea sedimentation, seabed geomorphological evolution, exploration and development of marine oil and gas resources, marine blue carbon sink and deep-water “source-sink” system. However, the specific process of transformation of hemp pits into submarine watercourses under the control of underflow activity is still unclear.

Taking the northwest of the South China Sea as an example, based on the measured data of seafloor topography, sedimentary environment and deep circulation, this study uses numerical simulation methods to reconstruct the transformation of hemp pits into submarine waterways under the action of undercurrents in this area. It is found that the existing and linear arrangement of seabed hemp pits (i.e., “hemp pit chain”) in the early stage changes the hydrodynamic characteristics of the bottom flow, which significantly strengthens the erosion of the bottom flow through the surface of the hemp pit, thereby connecting the discrete hemp pits in series to form the prototype of the submarine waterway (i.e. “immature waterway”), which also marks the beginning of the development of the seabed waterway.

The formation process is influenced by many factors such as the spacing of adjacent pits, the variation of the bottom flow velocity, and the characteristics of seafloor sediments. Further research found that there are three important key points in the process of underflow transformation of seabed hemp pits: first, compared with the upstream of the hemp pit, the downstream side wall of the hemp pit is more affected by the underflow erosion effect; Second, the erosion direction of the bottom flow is controlled by the spreading direction of the hemp pit chain; Third, the upwelling and downflow generated by the interaction between the side wall of the pit and the bottom flow are the key to controlling the erosion of the bottom flow.

Under the erosion of the bottom flow, the chain-like distribution of seafloor hemp pits are connected to each other to form the prototype of the submarine waterway (that is, the “immature waterway”). Photo courtesy of the research team

This study reveals the complex hydrodynamic process of seabed geomorphological evolution from seabed pits to seabed waterways, which can provide important theoretical support for the study of marine benthic ecosystems and the evolution of seafloor sedimentary environment.

The above research was jointly funded by the Natural Science Foundation of Guangdong Province-Outstanding Youth Program, the National Natural Science Foundation of China, and the “Talent Introduction Program” taken the lead of the Chinese Academy of Sciences. (Source: China Science News, Zhu Hanbin, Li Shu)

Related paper information:https://doi.org/10.1002/esp.5610



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