Abstract:

Internal wave solitons with amplitudes as large as 150 m propagate westward across the South China Sea, eventually interacting with the continental slope near Dongsha Atoll. Here, we present some of the first coherent observations of these waves from deep water (>500 m), through their shoaling transformation all the way to the surfzone at the Dongsha reef crest (<2 m). Three transformation phases are explored in detail as the internal waves encounter decreasing depths. Solitons begin to break (fission) in depths between 500 m and 100 m with characteristics controlled by the wave amplitude and phase speed. Farther upslope, between 300 m and 50 m depth, solitons transition to shoreward propagating bottom-trapped bores. Their shallow expression, in depths less than 20 m, was of an upslope propagating gravity current, at times driving bottom temperature variation of 10oC. These results quantify the complete shoaling, transformation and run-up evolution of internal wave solitons, and contextualize some of the world’s largest internal wave interactions with a sensitive coral environment.