Investigating the multicentennial oscillation of the AMOC using simplified ocean model

Paleoclimate evidences and coupled model studies suggested that the Atlantic Meridional Overturning Circulation(AMOC) has significant multicentennial variability. In this study, we use simplified two-dimensional and three-dimensional ocean model to extend previous theoretical and coupled model studies on the multicentennial oscillation(MCO) of AMOC, providing clearer physical insights and bridging the gap between idealized conceptual model and high-complexity numerical models. Our results demonstrate that stochastic salinity forcing effectively excites AMOC MCO, with the oscillation primarily driven by the tropical-subpolar advection feedback. Sensitivity experiments show that the period of the AMOC MCO is largely determined by the strength and vertical structure of the climatological AMOC: a stronger AMOC leads to a shorter oscillation period, while a deeper AMOC maximum results in a longer period. Under weak AMOC conditions, the oscillation timescale can extend to millennial scales. We also explore the role of wind-driven circulation and find that, although it has little influence on the MCO period, it slightly modifies the amplitude of variability by suppressing low-frequency components and enhancing high-frequency fluctuations. These simplified ocean model enables a systematic exploration of key physical mechanisms underlying AMOC MCO, offering valuable insights into long-term climate variability.