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The Indian Ocean has received limited attention in global assessments of anthropogenic radionuclides, despite its substantial role in inter-ocean exchange. Here we present distributions of Cs-137 and Pu-239,240, representative artificial radionuclides, in the western equatorial Indian Ocean between 2017 and 2023. Surface activities of Cs-137 and Pu-239,240 in the study region have decreased exponentially, corresponding to reductions of 19–48% for Cs-137 and 30–40% for Pu-239,240 over the past two decades. In the western Indian Ocean, the long-term decrease of Cs-137 is driven mainly by the surface current system, whereas Pu-239,240 is controlled predominantly by particle reactivity and vertical redistribution. The redistribution of Cs-137 indicates gradual lateral homogenization, with weak retention near the equator, suggesting that basin-scale mixing rather than meridional migration dominates its spatial distribution. The temporal evolution of Cs-137 and Pu-239,240 activities yields effective environmental half-lives of 24.8 ± 6.7 years and 10.1 ± 4.5 years, respectively, in the western Indian Ocean. These findings provide a comprehensive multi-decadal framework characterizing the western Indian Ocean not merely as a passive sink, but as a transit region where distinct oceanographic processes regulate the long-term redistribution of anthropogenic tracers.