New research suggests that iceberg discharge in the North Pacific may trigger weakening of the Atlantic Meridional Overturning Circulation (AMOC), a critical ocean current system, challenging decades of assumptions about its drivers.
For years, scientists believed that melting icebergs in the North Atlantic were the primary cause of past disruptions to the Atlantic Meridional Overturning Circulation (AMOC), a vital ocean current system responsible for redistributing heat across the globe. However, new research from the University of California, Davis, upends this theory, revealing that iceberg discharge in the North Pacific may actually be the root cause of AMOC weakening during ancient climate shifts.
A New Paradigm for AMOC Disruptions
The study, led by UC Davis assistant professor Chijun Sun, analyzed paleoclimate data and supercomputer simulations to trace the sequence of events during Heinrich stadials—periods of abrupt climate cooling in the Northern Hemisphere and warming in Antarctica. Contrary to previous assumptions, the research found that iceberg discharge in the North Pacific preceded and likely triggered AMOC weakening, which then led to increased iceberg melting in the North Atlantic.
“We found that North Pacific iceberg discharge events correlate very well with the onset of Heinrich stadials,” Sun said. “What’s more, they consistently lead to North Atlantic iceberg discharge events, so there might be a causal relationship there that has not been explored.”
How Pacific Icebergs Trigger Atlantic Changes
The simulations, which recreated conditions from 19,000 years ago, showed that freshwater from melting Pacific icebergs traveled across the globe, eventually reaching the North Atlantic. This influx of warm, fresh water diluted the AMOC’s dense surface waters, weakening the current and triggering further iceberg melt in the North Atlantic. The chain reaction highlights a “novel and surprising” mechanism where distant ocean basins are interconnected through freshwater dynamics.
“What is novel and surprising here is that North Pacific meltwater could independently drive AMOC weakening, offering a new paradigm for the trigger of Heinrich stadials,” Sun explained. The findings also have modern relevance: the same subsurface warming process observed in ancient ice ages is now accelerating the retreat of the West Antarctic Ice Sheet, according to the study.
Implications for Today’s Climate
The research underscores the fragility of the AMOC, which is already projected to weaken further by the end of this century. The UC Davis study provides a critical insight into the potential triggers of these shifts.
“We know that the subsurface warm water is causing rapid retreat of the West Antarctic Ice Sheet,” Sun said. “It was the same mechanism that drove some of the ice sheet retreat during the last deglaciation.” This connection between ancient and modern processes suggests that the same physical mechanisms driving past climate shifts are actively shaping today’s environment.
What Remains Uncertain
While the study provides a compelling new framework, questions remain about the precise timing and scale of future AMOC weakening. The UC Davis research emphasizes the need for further investigation into how freshwater inputs from distant regions might influence global ocean circulation. As climate models continue to evolve, the interplay between Arctic, Pacific, and Atlantic systems will likely remain a focal point for scientists.
For now, the findings challenge long-held assumptions and underscore the complexity of Earth’s climate system. As Sun noted, “It’s not only sensitive to whatever happened over the North Atlantic”—a reminder that understanding climate change requires looking beyond regional boundaries. The next steps will depend on refining these models and integrating data from global monitoring networks to predict how these ancient mechanisms might shape the future.
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