Climate Warming: A Paleoclimatic Perspective
New research shows, for the first time, an unprecedented and significant warming of equatorial Atlantic upper intermediate waters during the mid- to late Holocene
Boulder, Colo., USA: Against the backdrop of a rapidly warming climate, the need to better understand the mechanisms governing excess heat uptake and transfer into the deep ocean has become critically important. Between 1970 and 2020, approximately 89% of the excess heat arising from the accelerated increase in greenhouse gas emissions was absorbed by the oceans. Instrumental records and climate simulations indicate that subtropical and extratropical wind-driven ocean circulation plays a critical role in the uptake and transfer of excess heat into the ocean interior. However, evaluating the statistical significance of these observations is hindered by the short duration of instrumental records and the influence of natural climate variability.
Paleoclimatology, the study of ancient climate, provides an important perspective for understanding long-term climate response and ocean dynamics that cannot be gleaned from short-term observations. Using a marine sediment sequence from the equatorial Atlantic, Syee Weldeab of the University of California Santa Barbara reconstructed the temperature history of intermediate waters at a depth of 800 m over the last 11,000 years. The temperature record reveals a previously unrecognized, abrupt 5 °C warming that began approximately 5,700 years ago and reached peak warming 2,500 years ago. Remarkably, this outstanding warming at 800 m depth is not mirrored by changes in the overlying tropical sea surface temperatures, indicating an extratropical origin of the warming.
The timing of the subsurface warming coincides with major ocean–atmosphere circulation changes in the Southern Hemisphere. These changes were likely driven by increased solar insolation during the austral summer and include a poleward shift and intensification of the Southern Hemisphere Westerly Winds.
One important physical consequence of this wind strengthening is enhanced subduction of relatively warm surface waters equatorward of the zone of maximum wind stress, allowing these waters to descend into subsurface depths and propagate toward the tropical ocean interior. Weldeab proposes that the pronounced warming observed in the equatorial Atlantic intermediate waters is linked to these Southern Hemisphere ocean–atmosphere circulation changes, highlighting a mechanism by which high-latitude climate forcing can influence tropical subsurface ocean temperatures on centennial-to-millennial time scales.
The amount and persistence of equatorial warming at intermediate depth indicate a robust heat-transfer mechanism and underscore the capacity of the ocean to absorb and store large amounts of heat. The findings of this study provide an important paleoclimatic perspective on ongoing global warming, as the Southern Hemisphere westerly winds continue to shift poleward and strengthen, with important implications for future ocean heat uptake and interior-ocean warming.
Citation: Weldeab, S., 2026, Large mid to late Holocene warming of equatorial Atlantic intermediate waters: The role of the southern branch of the Meridional Overturning Circulation: Geology, v. 54, no. 6, p. 733–736, https://doi.org/10.1130/G54520.1
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