The Indonesian Throughflow (ITF), the only tropical pathway between oceans, impacts global ocean variability and climate through interactions with Indo-Pacific climate modes. Two important climate systems are the El Niño Southern Oscillation (ENSO) and East Asian Winter Monsoon (EAWM), which restrict surface ITF flow by driving low-salinity surface waters from the South China Sea into the western Indonesian Seas. Changes in South China Sea surface ocean pathways alter the magnitude of heat and freshwater carried by the ITF into the Indian Ocean, with global consequences. However, robust observational data only extends to the 1980s, hindering examination of the balance of ENSO and the EAWM influences on SCS surface ocean pathways. In addition, both ENSO and the EAWM reveal significant biennial variability that describes the poorly understood interactions of these systems. In this talk, I use seasonally resolved coral proxy records of ocean circulation (Δ14C and Ba/Ca) from the western Indonesian Seas to investigate biennial variability in ENSO and EAWM strength and interactions. I show that from 1945-1960, the EAWM strongly influences surface ocean pathways at biennial timescales. Following the 1960s, shifts in EAWM mean state and the frequency of central Pacific El Niño events coincide with reductions in the magnitude of the biennial signal and reversals in EAWM and ENSO influences on circulation. These changes in the balance of ENSO and EAWM influences serve as indicators for future changes in global heat distribution and Indo-Pacific climate, highlighting the importance of records that resolve EAWM-ENSO relationships beyond recent decades.