Oceanic Circulation Persists Even After Deep Water Formation Halt

The Atlantic Meridional Overturning Circulation (AMOC) is a crucial component of the climate system. Projections indicate that it should weaken due to global warming, raising concerns about a possible collapse and its climatic consequences. However, research suggests that wind-driven upwelling in the Southern Ocean may prevent the collapse of the AMOC, even in extreme warming scenarios ¹.

Models Indicate Persistence of Circulation

A recent study analyzed climate models under extreme warming conditions, such as the quadrupling of carbon dioxide levels. The results showed that the formation of North Atlantic Deep Water (NADW) may cease, but a trans-hemispheric overturning circulation can persist for centuries. This phenomenon is explained by a transient adjustment of the global ocean, which involves the progressive deepening of isopycnal surfaces, rather than sustained diapycnal sinking in the ocean interior ¹.

The researchers used the Community Earth System Model 2 (CESM2) from the National Center for Atmospheric Research. In a scenario of quadrupled CO2, the model showed a complete halt of NADW formation, but only a slow weakening of the trans-hemispheric circulation. Similar results were obtained with an idealized reduced-gravity ocean model, which simulates the key dynamics governing the overturning circulation ².

This continuous circulation can redistribute heat to deeper layers, mitigating surface warming. Additionally, it can reorganize ocean tracers, altering global patterns of nutrients and ventilation, which can have broad effects on ecosystems and global climate ².