Spatio-temporal variations of mixed layer depth in the Indonesian Seas

Abstract The mixed layer depth (MLD) within the Indonesian Seas demonstrates significant temporal and spatial variability. However, the detailed characteristics of these variations remain obscured due to the limitations of data resolution and disparities in calculation methodologies. This study employed the Copernicus Marine Environment Monitoring Service (CMEMS) global reanalysis data to derive MLD, utilized two criteria: temperature and density, then analyzed the spatial and temporal distribution characteristics and differences. The analysis reveals pronounced seasonal oscillations in MLD, with the temperature criterion-derived depth (Isothermal Layer Depth, ILD) generally larger than MLD determined by the density criterion. However, in the southern part of Timor Sea, the MLD is deeper than the ILD. The seasonal trends of ILD and MLD are well correlated (coefficient of 0.83), characterized by an initial decrease, followed by an increase, and another decrease and subsequent rise. In contrast, interannual variations display a negative correlation (coefficient of -0.44) between ILD and MLD. The findings can contribute to the understanding of hydrological characteristics, air-sea interactions, and the climate system within the Indonesian Seas.