10.7280/D1VH54
Davis, Kristen
0000-0001-8925-0433
University of California, Irvine
Arthur, Robert
Lawrence Livermore National Laboratory
Reid, Emma
University of California, Irvine
DeCarlo, Thomas
University of Western Australia
Cohen, Anne
Woods Hole Oceanographic Institution
Fringer, Oliver
Stanford University
Rogers, Justin
Stanford University
Data from: Fate of internal waves on a shallow shelf
Dryad
dataset
2020
National Science Foundation
https://ror.org/021nxhr62
1753317
2020-04-14T00:00:00Z
2020-04-14T00:00:00Z
en
912760221 bytes
4
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
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