Characterizing the Sound-Scattering Layer and Its Environmental Drivers in the North Equatorial Current of the Central and Western Pacific Ocean

Acoustic technology is an essential tool for detecting marine biological resources and has been widely used in sound-scattering layer (SSL) research. The North Equatorial Current (NEC) warm pool region of the Central and Western Pacific Ocean has a vast distribution of micronekton and zooplankton; analyzing the SSL characteristics in this region is vital for monitoring the marine environment and studying the marine ecosystem. In this study, we statistically analyzed the spatiotemporal factors of 10-200 m SSL in the NEC of the Central and Western Pacific Ocean using acoustic survey data collected by the Songhang research vessel (RV) in 2022, and the influence of environmental factors on the scattering layer distribution was analyzed using the Generalized Additive Model (GAM). The results showed that the SSL in the warm pool area of the NEC is distributed in shallow waters above 100 m. The primary scatterers are micronekton and zooplankton, and this SSL had diel vertical migration behavior. By comparing Akaike's Information Criterion of different GAMs, the model consisting of six factors, namely, temperature, current velocity, turbidity, solar altitude angle, longitude, and latitude, was remarkable. Each model's factor effects primarily influence the contribution of the volume-backscatter strength (Sv). The cumulative deviation explanation rate of the Sv was 67.2%, among which the highest explanation rate of solar altitude angle variance was 35.4%, the most critical environmental factor. The results of this study can provide a reference for long-term studies on ecological changes and their effects on micronekton and zooplankton distribution.

Automated summary

In this study, acoustic survey data collected by the Songhang research vessel in 2022 were used to analyze the spatiotemporal factors and environmental influences on the sound-scattering layer (SSL) in the North Equatorial Current (NEC) warm pool region of the Central and Western Pacific Ocean. It was found that the SSL in this region is primarily distributed in shallow waters above 100 m and consists of micronekton and zooplankton with diel vertical migration behavior. Factors such as temperature, current velocity, turbidity, solar altitude angle, longitude, and latitude were identified as important in influencing the SSL distribution. The results of this study have implications for long-term studies on ecological changes and their impact on micronekton and zooplankton distribution.