1019 / 2024-09-20 07:46:57

Temporal and Spatial Variations of Internal Tides at Seamounts

internal tides,wave-wave interaction,seamounts

Session 70 - Internal Waves and Ocean Mixing

Seamounts are ubiquitous topographic features in global oceans, and their influences on local oceanic circulation as well as ocean mixing have attracted great attention in Physical Oceanography. When the barotropic tidal flow impinges on a seamount, the internal tides (internal waves with tidal frequency) are generated. Related to internal tidal activity, the mechanism of water mixing and deep-water coral feeding, as well as the formation of cobalt-rich crusts, remains unclear. Caiwei Guyot, located in the western Pacific Ocean, is the third largest guyot on Earth and forms part of the Magellan Seamounts. Its unique geophysical and biological features have been revealed, while the physical processes such as internal tides within the region have not yet been discovered. In this study, the characteristics of internal tides are investigated by using 7 long-term ADCP moorings as well as other supplementary observations. Energy spectra demonstrate significant differences in energy distribution among locations. In general, the energy spectra of the station at the summit of the mountain exhibit a GM spectrum form slope, whereas it is absent for the station at the edge of the mountain. This missing might indicate a weak wave-wave interaction. Internal tides are significant at Caiwei Guyot. Energy peaks can be seen clearly in D1 and D2 bands at all stations, while D2 energy dominates. Specifically, the internal tidal energy on stations at the edge of the mountain exceeds that at the central summit. The temporal variation of internal tidal energy can be highly complex. The spring-neap cycle is predominant, while seasonal variation is negligible, especially for observations near the bottom. It can be inferred that the internal wave breaking and the mixing it induced at the ocean interior around seamounts varies little. The internal tides near the surface are rather sophisticated and show little correlation with barotropic tides. As surrounded by other seamounts, the internal tides, as well as the mixing it induced, can be disrupted by remote internal tidal sources. A numerical model is also conducted to give qualitative access to this interference. Our findings here provide information on internal tides on a typical guyot in the west Pacific. Further study is required to provide insight into the mechanisms of interaction between seamount internal tides and background processes.