<p>Over the past four decades, the upper-ocean memory—defined as the persistence of ocean conditions—in the Maritime Continent (MC) region has undergone an interdecadal transition, which was initially relatively strong before rapidly degrading from the early twenty-first century. Yet the physical origins of this trend remain poorly understood. This study disentangles the contributions of internal decadal variability—represented by the Interdecadal Pacific Oscillation (IPO)—and externally forced climate change to this phenomenon. During IPO-positive phases, surface buoyancy loss associated with intensified evaporation and net heat flux out of the ocean, coupled with negative anomalous wind stress curl, deepens the ocean mixed layer through enhanced Ekman downwelling. Simultaneously, large-scale westerlies trigger Rossby wave propagation that adjusts the thermocline and strengthens vertical mixing. These coupled processes enhance upper-ocean inertia and sustain ocean memory. Conversely, IPO-negative conditions promote shallower mixed layers and memory degradation. Using attribution analysis, we further demonstrate that anthropogenic warming contributes approximately 67.6% to the long-term memory decline, primarily by increasing upper-ocean stratification and suppressing vertical heat exchange. Our results offer a dynamical framework for understanding the interplay between natural and human-induced climate warming in shaping long-term ocean memory variability in the MC region.</p>