This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: New high-resolution speleothem records from China and India, together with isotope-enabled climate models, show that abrupt glacial ocean circulation recoveries took centuries, not decades—a finding with important implications for how we assess future Atlantic circulation change. The work is published in the journal Science.
Dansgaard–Oeschger (DO) warm events saw high-latitude Northern Hemisphere temperatures rise by 5–16 °C, closely linked to strengthening of the Atlantic meridional overturning circulation (AMOC), and are widely used as an analog for future AMOC change. Existing studies suggest AMOC strengthening during DO events occurred within decades, but this rests on ice-core δ¹⁸O records, a signal influenced by both temperature and moisture source. Speleothem δ¹⁸O from India and southwest China responds directly to AMOC-driven changes, offering an independent test—but existing records lacked the chronology and annual-layer constraints needed to quantify transition rates.
Two annually laminated speleothems from Cherrapunji Cave (northeast India) and Shuixi Cave (southwest China), together with published records from Zhangjia Cave, yielded high-resolution δ¹⁸O series spanning DO-1 to DO-8. The transitions consistently lasted longer than 100 years, averaging about 180 years—far longer than the decadal-scale shifts in Greenland ice-core δ¹⁸O records. "The speleothems used in this study have clear annual laminae, which is essential," said Dr.
"U–Th dating gives us precise absolute ages, but it cannot give reliable relative ages. The annual laminae let us precisely constrain how long each transition lasted and compare that directly with the Greenland ice-core records." Modeling reveals a two-stage process: the retreat of sea ice in the northeastern North Atlantic triggered a rapid adjustment of regional atmospheric circulation from stadial to interstadial conditions, causing the sharp rise in Greenland δ¹⁸O. Subsequently, the AMOC strengthened further and sea ice in the northwestern North Atlantic continued to retreat, but atmospheric circulation modes and moisture transport pathways did not change significantly, so Greenland δ¹⁸O showed no further marked fluctuation.
The simulations show that Asian monsoon speleothem δ¹⁸O records capture the full AMOC strengthening process. "This work clarifies the relationship between Asian speleothem δ¹⁸O, Greenland ice-core δ¹⁸O and the AMOC, which is an important step toward understanding abrupt climate change," said Professor Hai Cheng. "This work shows that natural AMOC transitions were not as fast as researchers previously inferred from ice-core records.
Therefore, when we talk to the public about the risk of AMOC tipping in the future, we need to be clearer about how long that transition would take. That matters just as much as the climate impacts it could cause," Dong added. "The study demonstrates the value of combining high-quality paleoclimate records with process-based modeling: annually laminated speleothem records provide essential observational constraints for quantifying the rates of abrupt climate transitions, while isotope-enabled Earth system models provide the theoretical framework for interpreting the underlying dynamics," Xu Zhang said.
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