The Doomsday Hintercast - Oceans in Flux
Recent research indicates that the Southern Ocean’s overturning circulation is weakening due to rapid Antarctic ice melt and the resulting influx of freshwater into surface waters. This freshwater reduces the density of surface water, inhibiting the formation of dense, cold Antarctic Bottom Water—the process that drives the deep, southward limb of the global overturning circulation. As this sinking slows, the overall strength of the circulation is declining, disrupting the ocean’s ability to absorb heat and carbon from the atmosphere and transport them into the deep ocean. Observations from oceanographic instruments show these changes are already underway and could lead to significant disruptions in global climate patterns if warming continues.
Separately, studies published in Nature Communications and other journals have found that the Atlantic Meridional Overturning Circulation (AMOC)—which includes the Gulf Stream—is likely at its weakest in more than a millennium, largely due to warming waters and increased freshwater from melting ice. Some models suggest the AMOC may be approaching a tipping point under continued emissions.
These two systems, though located in opposite hemispheres, are part of the same global thermohaline network. Changes in one can influence the other over time through interconnected oceanic and atmospheric feedbacks. Together, they signal that the deep circulatory systems anchoring Earth’s climate are destabilizing. The consequences are already emerging: accelerated sea-level rise along the U.S. East Coast, shifts in marine ecosystems, altered weather patterns, and disruptions to rainfall systems such as the Sahel in Africa and monsoon regions across Africa and Asia. These changes are measured, recorded, and underway.
[Nature Climate Change, 2023] [Nature, 2021] [Nature Communications, 2021] [CSIRO, 2024] [NOAA Climate.gov, 2024] [IPCC AR6 Report, 2021]
*This article was originally published in the July 2025, Sturgeon Moon Cycle issue of our email newsletter the Liminal.
