Spatial And Temporal Distribution Characteristics Of Acoustic Scattering Layer In The Central North Pacific Ocean

In recent years,more and more attention has been paid to the study of the acoustic scattering layer and its diel vertical migration.The acoustic scattering layer is a layer of water in the ocean which is strongly backscattered due to the concentration of plankton and fish.It is common in the global oceans and freshwater lakes.In this paper,the sound scattering layer and its diurnal vertical migration in the Central North Pacific Ocean are analyzed and studied,and the correlation between the surrounding ocean physical environment parameters and the acoustic scattering layer and its migration phenomenon is analyzed,so as to further understand the occurrence mechanism and excitation factors of the circadian diel vertical migration of the acoustic scattering layer.This paper mainly includes the following aspects:(1)There are generally two acoustic scattering layers in the central North Pacific Ocean,the depth of the upper scattering layer is between 0-200 m,and the depth of the deep scattering layer is between 350m-550m;in some sea areas and time periods,there will be a third scattering layer with the depth of about 550m-600 m.(2)In the daytime,the intensity of the upper scattering layer is weakened,and the intensity of the deep scattering layer is strengthened;at night,the intensity of the upper scattering layer is strengthened,and the intensity of the deep scattering layer is weakened.This is due to the vertical migration of plankton and fish in the scattering layer.This paper explores the law and mechanism of this phenomenon.(3)There is a certain correlation between the light intensity and the depth and time of the day night migration of the acoustic scattering layer.In the seasons and months with high light intensity and long illumination time,the migration depth of scattering layer is deep and the migration time is long;for seasons and months with short illumination time,the migration depth of scattering layer is shallow and the migration time is short.(4)There is also a certain correlation between the acoustic scattering layer and the physical parameters of the surrounding seawater.There is a certain correlation between the migration depth of the acoustic scattering layer and the temperature,salinity anddissolved oxygen content of the surrounding seawater,but the correlation between the contents of nutrients such as N,P and the scattering layer is not strong.