Spatio-temporal variations of the thermocline and its correlation with ENSO in the Indonesian Seas

Abstract The thermocline in the Indonesian seas exhibits significant variability; however, its temporal and spatial characteristics have not been well elucidated. This study employs high-resolution reanalysis data, combined with the temperature gradient method, to reveal the spatio-temporal variations of the depths of upper boundary, lower boundary, and thickness of the thermocline in the Indonesian seas, as well as their interannual correlation with ENSO. The results indicate that in the shallow seas, the thermocline thickness is relatively thin with pronounced seasonal variations, while in the deep seas, the thermocline thickness is thicker with distinct monthly changes. The thermocline thickness displays two maximums and minimums in one year. The interannual variation of the thermocline is negatively correlated with the ENSO index (correlation coefficient of -0.48), and spatial correlation analysis reveals that the ENSO phenomenon primarily impacts the inflow and outflow seas of the Indonesian Throughflow. These findings are significant for understanding the variation patterns of the thermocline in equatorial waters.