Ocean Memory Loss in the Maritime Continent: A Dual Influence of Natural Decadal Oscillations and Human-Induced Warming

Abstract The Maritime Continent (MC) region has undergone a sustained decline in upper-ocean thermal memory over recent decades, 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, coupled with 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 processes in shaping long-term ocean memory variability in the MC region.