Ancient sediments reveal Atlantic circulation stayed robust despite near-shutdown of Agulhas flow

An international team analyzed microplankton fossils and lipid biomarkers from a core drilled on the Agulhas Plateau, alongside temperature proxies from the northern Gulf of Mexico and other Atlantic sites. The data reveal that, during a brief glacial episode in the late Pliocene, the subtropical front shifted northward, cooling the Agulhas region by about 3 °C and nearly halting the salty water influx into the Atlantic.

Contrary to textbook expectations, the Atlantic Meridional Overturning Circulation did not weaken; instead, North Atlantic Deep Water production and lower-latitude overturning grew stronger, producing a shallower thermocline across the basin. Climate-model runs reproduced this pattern, suggesting that the controls on Atlantic circulation can change with climate state. The findings imply that future shifts in ocean fronts may alter the mechanisms driving the AMOC, though the study cautions against direct extrapolation to present-day warming. The work was funded by the European Research Council under the OceaNice project.