Verification of the internal tide off Zhiben coast, Taitung, southeast Taiwan

  • Deep ocean water from an industrial pipeline was monitored continuously
  • Variations of nutrient concentrations showed a semi-diurnal cycle
  • Physical measurements revealed similar oscillating scales or frequencies
Abstract

An oscillating vertical movement of the undersurface water layers has been verified off the coast of Zhiban, Taitung, southeast Taiwan. It was first suspected to exist by significant variations of CTD temperature profiles observed on Cruises OR3-1769 and OR3-1792 in 2014. A frequency of 12.5 hr-1 was estimated from temperature record by a subsurface ADPC moored at a depth of 110 m. Further proofs were obtained in 2016 by chemical measurements of silicate and phosphate in an industrial pipeline which takes up continuously the deep ocean water at a depth of 319 m. The nutrient concentrations varies hour by hour during a 36-hr period (0.88-1.11 μM for phosphate and 19.0-26.2 μM for silicate), showing a semi-diurnal cycle which matched well with that of the surface tide reported at a near-by tidal station. An amplitude of 60-100 m that occurs in a semidiurnal cycle can be commonly observed in this area at depths between 100 and 300 m.

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