Rapid changes in the near-bottom temperature of the bottom aquaculture area around the Zhangzi Island in summer

Rapid changes in the near-bottom water temperature are important environmental factors that can significantly affect the growth and development of species in the bottom culture.The object of this research is to investigate the mechanism causing these rapid changes within a bottom culture area near the Zhangzi Island.The hydrographic transects observations in the North Yellow Sea(NYS)suggest that our mooring station is very close to the tidal mixing front.The horizontal advection of the tidal front has induced the observed tidal change of bottom temperature at the mooring station.Analysis of the mooring near-bottom temperature and current measurements show that the angle between the tidal current horizontal advection and the swing of the tidal front is crucial in determining the variation trend of temperature.When the angle equals 90°,the horizontal tidal current advects along the isotherms so the temperature remains the same.When the angle is between 0°and 90°,the seawater moves from deep water to the warmer coastal zone and the temperature decreases.In contrast,the horizontal tidal advection moves the coastal warm water to the mooring station and the water temperature increases when the angle is between 90°and 180°.The amplitude of the temperature change is proportional to the magnitude of the horizontal temperature gradient and the tidal excursion in the direction of the temperature gradient.This study may facilitate the choice of culture area in order to have a good aquaculture production.