Multistability and intermediate tipping of the Atlantic Ocean circulation

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Tipping points (TP) in climate subsystems are usually thought to occur at a well-defined, critical forcing parameter threshold, via destabilization of the system state by a single, dominant positive feedback. However, coupling to other subsystems, additional feedbacks, and spatial heterogeneity may promote further small-amplitude, abrupt reorganizations of geophysical flows at forcing levels lower than the critical threshold. Using a primitive-equation ocean model, we simulate a collapse of the Atlantic Meridional Overturning Circulation (AMOC) due to increasing glacial melt. Considerably before the collapse, various abrupt, qualitative changes in AMOC variability occur. These intermediate tipping points (ITP) are transitions between multiple stable circulation states. Using 2.75 million years of model simulations, we uncover a very rugged stability landscape featuring parameter regions of up to nine coexisting stable states. The path to an AMOC collapse via a sequence of ITPs depends on the rate of change of the meltwater input. This challenges our ability to predict and define safe limits for TPs.

TidsskriftScience Advances
Udgave nummer12
Antal sider14
StatusUdgivet - 2024

Bibliografisk note

Funding Information:
Acknowledgments: We thank R. nuterman and the danish center for climate computing for supporting the simulations with the veros ocean model and U. Feudel, P. Ashwin, and A. Keane for valuable discussions. Funding: the project has received funding from the european Union’s horizon 2020 research and innovation programme under grant agreement no. 820970 and from danmarks Frie Forskningsfond under grant no. 2032-00346B. h.A.d. was funded by the european Research council through the eRc-AdG project tAOc (project 101055096). Author contributions: J.L. designed and performed the research. the paper was written by J.L. with input from all co-authors. All authors discussed and interpreted the results. Competing interests: the authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. the raw model simulation data that underlie the findings of this study are deposited in the electronic Research data Archive repository of the University of copenhagen and can be accessed at hpsKecpv8G.

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© 2024 American Association for the Advancement of Science. All rights reserved.

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