Abstract
There exists a warming deficit in sea surface temperatures (SST) over the subpolar North Atlantic in response to quadrupled CO2, referred to as the projected North Atlantic warming hole (WH). This study employs a partial coupling technique to accurately verify the relative roles of oceanic and atmospheric processes in the formation of the projected WH within an atmosphere-ocean coupled framework. By decomposing the SST anomalies in the subpolar North Atlantic into two components: those induced by atmospheric processes (i.e., the atmosphere-forced component) and those driven by changes in ocean circulation (i.e., the ocean-driven component), we find that the projected WH is primarily driven by changes in ocean circulation, with almost no contribution from atmospheric processes. Specifically, the slowdown of the Atlantic Meridional Overturning Circulation (AMOC) results in a cooling of SST in the WH region due to reduced northward ocean heat transport into this region. This study further quantifies the influence of a positive coupled feedback through surface heat flux (SHF) on the AMOC response under greenhouse gas forcing within this self-consistent framework. It is found that the AMOC slowdown leads to a negative SST anomaly in the subpolar North Atlantic and subsequently a positive ocean-driven SHF anomaly, which in turn further weakens the AMOC. This positive feedback through the SHF contributes about 50% to the total AMOC slowdown in response to quadrupled CO2.
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The CESM data used in this study are available from the corresponding author upon request.
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Acknowledgements
We acknowledge Dr. Oluwayemi Garuba for sharing the data of the fully and partially coupled experiments with tracers. This work is supported by the National Natural Science Foundation of China (NSFC; 42230405) and the Laoshan Laboratory (No. LSKJ202202401). This research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory, operated under Contract No. DE-AC02-05CH11231 using NERSC award ERCAP0017151. J. L. is supported by the U.S. Department of Energy Office of Science Biological and Environmental Research as part of the Regional and Global Model Analysis program area. Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under contract DE-AC05-76RL01830. F. L. is supported by the “Youth Innovation Team Program” Team in Colleges and Universities of Shandong Province (No. 2022KJ042) and Fundamental Research Funds for the Central Universities (No. 202341016).
Funding
This work is supported by the National Natural Science Foundation of China (NSFC; 42230405) and the Laoshan Laboratory (No. LSKJ202202401).
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Y. Luo, J. Lu and F. Liu were responsible for design of the research. The first draft of the manuscript was written by Q. Li and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
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Li, Q., Luo, Y., Lu, J. et al. Roles of the atmosphere and ocean in the projected north atlantic warming hole. Clim Dyn (2024). https://doi.org/10.1007/s00382-024-07289-w
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DOI: https://doi.org/10.1007/s00382-024-07289-w