Data from: Fate of internal waves on a shallow shelf

  • Kristen A. Davis (Creator)
  • Robert Arthur (Contributor)
  • Emma C. Reid (Creator)
  • Thomas DeCarlo (Creator)
  • Anne L. Cohen (Creator)
  • Oliver Fringer (Creator)
  • Justin S. Rogers (Creator)

Dataset

Description

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 narrow shelf-slope region in the South China Sea. The spatially-continuous view of temperature fields provides a perspective of physical processes commonly available only in laboratory settings or numerical models, including internal wave reflection off a natural slope, shoreward transport of dense fluid within trapped cores, and observations of internal run-down (near-bed, offshore-directed jets of water preceding a breaking internal wave). Analysis shows that the fate of internal waves on this shelf – whether transmitted into shallow waters or reflected back offshore – is mediated by local water column density structure and background currents set by the previous shoaling internal waves, highlighting the importance of wave-wave interactions in nearshore internal wave dynamics.,In this paper we present observations of internal waves shoaling on the shallow shelf-slope of Dongsha Atoll, a coral reef ecosystem in the South China Sea (Fig. 1a-c). Dongsha is directly in the path of some of the world’s largest internal solitary waves [Alford, 2015; Guo and Chen, 2014; Hsu, 2000; Lien et al., 2005]. These waves evolve from steepened internal tides in Luzon Strait and propagate westward across the deep basin of the northern South China Sea with wavelengths of O(3-10 km), often developing into wave trains [Alford, 2015]. As the solitary waves shoal up onto the continental slope they steepen even further with amplitudes as large as 150-200 m and wavelengths of only a few hundred meters. At this point they can become susceptible to both convective and shear instabilities which cause them to break and drive huge vertical overturns, energetic mixing, and energy dissipation [Chang et al., 2006; St. Laurent, 2008]. The shallow (< 25 m) slope of Dongsha Atoll is an internal swash zone, where the end-of-life of these large internal waves takes the form of bottom-propagating solibores and boluses. They spend their remaining energy bringing deep water up to the surface where it has significant effects on the reef heat and nutrient budgets [Reid et al., 2019]. From 1-17 June 2014, we deployed Distributed Temperature Sensing (DTS) instrumentation to capture spatially-continuous observations of near-bed temperature on the fore reef slope of Dongsha Atoll to evaluate the path (or “fate”) of internal waves shoaling onto the shelf and moorings to measure the vertical structure of velocity and density stratification. A semi-idealized numerical simulation is used to help interpret the novel perspective provided by the DTS observations. Here a four-channel DTS system (Sensornet Oryx) was used to capture a continuous view of near-bed temperature in a cross-shelf profile on the east fore reef of Dongsha Atoll. Four kilometers of Kaiphone 0.6 cm-diameter fiber optic cable was deployed in a cross-shelf orientation (285°, aligned approximately parallel to the propagation direction of the offshore internal wave field [Ramp, 2010], beginning at the back of the reef flat (~2 m depth) and terminating offshore at 50-m depth on the fore reef (Fig. 1c). In this study we focus on the offshore-most ~1 km of the FO cable - from the reef crest down the fore reef slope – the reader is referred to Reid et al. [2019] for further information about the shallow reef DTS results. The FO cable followed the bottom contours of the bed, except in areas with extreme changes in topography (such as a coral groove) where the cable was raised above the bed by up to 0.5 m. The DTS collected temperature traces along the cable every minute with 2-m spatial resolution from 2-12 June 2014. A tropical storm in the vicinity of Dongsha Atoll reduced solar power and prevented further DTS measurements after 12 June, however, measurements from vertical arrays (Section 2.3) continued until 17 June 2014.,Notes on E1 Mooring and DTS Calibration and Validation loggers located in data folders,
Date made available14 Apr 2020
PublisherDryad Digital Repository

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