Indonesian Seas Circulation Linked to Mean Climate State Reversals

Abstract The Indonesian Throughflow (ITF) plays a critical role in modifying global ocean and climate systems through interactions with Indo‐Pacific climate. The El Niño Southern Oscillation (ENSO) and East Asian Winter Monsoon (EAWM) alter the spatial distribution of surface layer freshwater within the Maritime Continent, which affects heat and freshwater distribution from the Pacific to the Indian Ocean via the ITF. Yet, limited observations prior to the 1980s hinder examination of the role of ENSO and the EAWM on surface layer variability. Here, we use coral Δ 14 C and Ba/Ca records as proxies of ocean circulation from locations along main ITF pathways to investigate behavior in EAWM and ENSO strength and interaction. We focus on biennial variability given that the biennial modulation of the ENSO‐EAWM relationship remains a critical gap in understanding their interaction. From 1953 to 1963, the EAWM influences surface layer pathways at biennial timescales. Following 1963, shifts in EAWM mean state and the frequency of central Pacific El Niño events coincide with lower biennial variance and modulations of EAWM‐ and ENSO‐driven surface layer circulation. These historical ENSO and EAWM influences provide insight into future ITF variability and its associated global impacts.