Large waves deep within oceans shape the seafloor
Large waves deep within oceans shape the seafloor lead image
Under the sea just above the ocean floor lies the marine nepheloid layer (MNL), where large amounts of sediment are suspended in water. Internal solitary waves (ISWs) – large, strong currents that follow the lunar cycle – can have significant effects on the MNL and potentially causing changes to the landscape of the seabed.
Tian et al. studied the effects of ISWs on MNLs and sediment resuspension. Cruising a research vessel through the northern South China Sea, they took measurements of the concentration of suspended particulate matter close to the ocean floor while monitoring nearby ISWs, and analyzed the topography of the seabed.
Profiles of suspended particles suggested that ISWs primarily affect sediment at depths down to 1,500 meters beneath the ocean surface, with the majority of the impacts observed below 1,000 meters, where ISWs heavily disturb seabed sediments and reshape the bedform. The effects were significant below 700 meters, with very large volumes of suspended particulate matter.
Overall, the group found it clear that ISWs induce sediment suspension and transport near the bottom of the seabed, affecting the seabed landscape and eroding its slope.
Author Zhuangcai Tian said the same mechanism could be at play in other partially enclosed areas of the ocean, though additional studies are needed to fully explain the role of ISWs on seabed sediment.
“We can measure the sedimentation rate and thickness of the seabed sediment on the northern South China Sea in the future, and quantitatively analyze the suspension and transport of sediment by ISWs,” said Tian.
Source: “Internal solitary waves induced deep-water nepheloid layers and seafloor geomorphic changes on the continental slope of the northern South China Sea,” by Zhuangcai Tian, Yonggang Jia, Jiangxin Chen, J. Paul Liu, Shaotong Zhang, Chunsheng Ji, Xiaolei Liu, Hongxian Shan, Xuefa Shi, and Jiwei Tian, Physics of Fluids (2021). The article can be accessed at https://doi.org/10.1063/5.0045124 .
