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Abstract Large nonlinear internal solitary waves (NLIWs) are known to transit west northwest across the northeastern South China Sea from generation sites around the two‐ridge system in the Luzon Strait. The waves are important because their energy flux and dissipation are several orders of magnitude larger than the surrounding ocean. The wave transit has been well studied up to about the 100 m isobath but observations in shallower water have been scarce. Using oceanographic moorings and an innovative distributed temperature sensing optical cable, the NLIW transformations were observed from 2000 to 2 m on the flanks of Dongsha Atoll (Pratas Reef). Possible outcomes included reflection, refraction around the island, wave breaking, and penetration into shallow water. Upslope penetration depended on incident wave amplitude and direction as well as the local stratification.
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Internal waves influence the thermal and nutrient environment on a shallow coral reef
Abstract Internal waves can influence water properties in coastal ecosystems through the shoreward transport and mixing of subthermocline water into the nearshore region. In June 2014, a field experiment was conducted at Dongsha Atoll in the northern South China Sea to study the impact of internal waves on a coral reef. Instrumentation included a distributed temperature sensing system, which resolved spatially and temporally continuous temperature measurements over a 4‐km cross‐reef section from the lagoon to 50‐m depth on the fore reef. Our observations show 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 flow, where it significantly alters the water temperature and nutrient concentrations on the reef flat. We find that without internal wave forcing on the fore reef, temperatures on the reef flat could be up to 2.0°C ± 0.2°C warmer. Additionally, we estimate a change in degree heating weeks of 0.7°C‐weeks warmer without internal waves, which significantly increases the probability of a more severe bleaching event occurring at Dongsha Atoll. Furthermore, using nutrient samples collected on the fore reef during the study, we estimated that instantaneous onshore nitrate flux is about four‐fold higher with internal waves than without internal waves. This work highlights the importance of internal waves as a physical mechanism shaping the nearshore environment, and likely supporting resilience of the reef.
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- PAR ID:
- 10460806
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 64
- Issue:
- 5
- ISSN:
- 0024-3590
- Page Range / eLocation ID:
- p. 1949-1965
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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