Observations of nonlinear internal wave evolution and mixing from the shelf to the surf zone.

Internal waves strongly influence the physical and chemical environment of coastal ecosystems worldwide. We report novel observations from a distributed temperature sensing (DTS) system that tracked the transformation of internal waves from the shelf break to the surf zone over a shelf-slope region of a coral atoll in the South China Sea. The spatially-continuous view of the near-bottom temperature field provided by the DTS offers a perspective of physical processes previously available only in laboratory settings or numerical models. Additionally, we report observations of turbulent dissipation during the passage of a shoaling internal wave train and examine the implications for irreversible mixing of subthermocline water into the nearshore region and onto a shallow coral reef. We find that during summer, internal waves shoaling on the shallow atoll regularly transport cold, nutrient-rich water shoreward, altering near-surface water properties on the fore reef. This water is transported shoreward of the reef crest by tides, breaking surface waves and wind-driven \textunderscore ow, where it signi\textunderscore cantly alters the water temperature and nutrient concentrations on the reef \textunderscore at.