Zhou et al. (2026) Self-sustained multicentennial oscillation of the Atlantic meridional overturning circulation in two-hemisphere box models

Identification

• Journal: Climate Dynamics
• Year: 2026
• Date: 2026-01-01
• Authors: Xiangying Zhou, Kunpeng Yang, Haijun Yang, Qiong Zhang
• DOI: 10.1007/s00382-025-07947-7

Research Groups

• Department of Atmospheric and Oceanic Sciences and Key Laboratory of Polar Atmosphere-Ocean-Ice System for Weather and Climate of Ministry of Education, Fudan University, Shanghai, China
• Department of Physical Geography and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden

Short Summary

This study develops a two-hemisphere box model to investigate the self-sustained multicentennial variability of the Atlantic Meridional Overturning Circulation (AMOC), finding a robust, weakly damped oscillation primarily controlled by North Atlantic salinity advection feedback, with the thermohaline component being necessary and sufficient for its existence.

Objective

• To develop a two-hemisphere box model of the Atlantic Meridional Overturning Circulation (AMOC) to investigate the robustness and underlying mechanisms of its self-sustained multicentennial oscillations, clarifying the roles of thermohaline and wind-driven components and basin geometry.

Study Configuration

• Spatial Scale: A two-hemisphere box model consisting of six ocean boxes, with a zonal width of 5200 km and a meridional extent of 140°, separated into three zones by latitudes 45°N and 30°S (representing subpolar North Atlantic, tropical oceans, and subpolar South Atlantic).
• Temporal Scale: Multicentennial variability, with oscillation periods typically around 340 years and e-folding times ranging from hundreds to thousands of years.

Methodology and Data

• Models used:
  • Two-hemisphere box models:
    • 6-box salinity-only model (6S model)
    • 6-box temperature-salinity model (6TS model), including variants with only thermohaline circulation (6TSTHC) and with both thermohaline and wind-driven circulations (6TSTHC + WDC)
    • Simplified 3-box salinity model (3S model) for analytical solutions (also 4S and 5S models for intermediate simplifications)
• Data sources:
  • Community Earth System Model (CESM, version 1.0) coupled model simulations
  • EC-Earth3-LR coupled climate model output
  • Proxy data (for observed multicentennial variability)
  • Observational data (for parameter selection)

Main Results

• A robust, weakly unstable multicentennial eigenmode (period approximately 340 years, e-folding time approximately 930 years) persists in the two-hemisphere box model.
• Self-sustained multicentennial oscillations are realized by introducing enhanced vertical mixing in the subpolar North Atlantic.
• Salinity advection feedback in the North Atlantic is the dominant control mechanism for the oscillation, with the South Atlantic playing a minor role.
• The self-sustained multicentennial oscillation is easier to occur and less sensitive to changes in basin geometry in the two-hemisphere model compared to one-hemisphere models.
• Analytical solutions from a simplified 3S model show that the oscillation period is primarily controlled by basin geometry and mean AMOC strength.
• The inclusion of wind-driven circulation weakens the oscillation amplitude by approximately 30% (e.g., AMOC anomaly from 0.35 Sv to 0.23 Sv) but has a negligible impact on the oscillation period (changing from approximately 330 years to 340 years).
• The thermohaline component of the AMOC is a necessary and sufficient condition for the multicentennial oscillation in this model; purely wind-driven overturning cannot exhibit such oscillations.

Contributions

• Extends previous one-hemisphere box models to a symmetric two-hemisphere configuration, offering a more realistic parameterization of the AMOC anomaly as a function of meridional density difference.
• Dramatically reduces the sensitivity of eigenmodes to precise basin geometry and layer division, and provides a compact analytical formula for the oscillation period.
• Analytically proves that thermohaline overturning is both necessary and sufficient for centennial-millennial oscillations, and explains why a purely wind-driven overturning cannot oscillate on these timescales.
• Offers a clear, physically interpretable framework for understanding multicentennial AMOC oscillations, bridging conceptual box models and fully coupled simulations.
• Demonstrates that ocean dynamics alone, via thermohaline and wind-driven overturning, can sustain a multicentennial eigenmode, providing a logical foundation for understanding AMOC variability.

Funding

• National Natural Science Foundation of China (Grant Nos. 42230403, 42288101, 41725021, 91737204)
• Shanghai Frontiers Science Centre of Atmosphere-Ocean Interaction of Fudan University
• Swedish Research Council (2022-03129, 2022-06725)
• Swedish Foundation for International Cooperation in Research and Higher Education (STINT: MG2022-9298)
• Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Centre (NSC)

Citation

@article{Zhou2026Selfsustained,
  author = {Zhou, Xiangying and Yang, Kunpeng and Yang, Haijun and Zhang, Qiong},
  title = {Self-sustained multicentennial oscillation of the Atlantic meridional overturning circulation in two-hemisphere box models},
  journal = {Climate Dynamics},
  year = {2026},
  doi = {10.1007/s00382-025-07947-7},
  url = {https://doi.org/10.1007/s00382-025-07947-7}
}