The Impact of the AMOC Resumption in the Western South Atlantic Thermocline at the Onset of the Last Interglacial

After glacial terminations, large amounts of heat and salt were transferred from low to high latitudes, which is a crucial phenomenon for the reestablishment of the Atlantic Meridional Overturning Circulation (AMOC). However, how different glacial terminations evolved in the (sub)tropics is still poorly documented. Here we use foraminifera oxygen (δ18O) and carbon (δ13C) stable isotopes to show that the North Atlantic heat piracy, following the AMOC resumption at the early Last Interglacial, affected the thermocline δ18O levels of the subtropical western South Atlantic. Because of the cooling imposed by this process, glacial δ18O persisted in the thermocline for ~7 kyr after the onset of the Last Interglacial, dampening the effect of sea level rise usually imprinted on foraminifera δ18O during terminations. Faunal composition and δ13C also suggest the existence of a colder and thicker South Atlantic Central Water coeval with the AMOC recovery. This process apparently did not occur during the last deglaciation. Plain Language Summary Glacial terminations are periods of fast ice sheet disintegration, elevation of global temperatures, and release of carbon dioxide from the deep ocean to the atmosphere. These conditions turn such intervals well situated to the study of global climate changes. The warming of high latitudes is supported by the transfer of heat and salt from low latitudes. However, the documentation of how glacial terminations occurred in low‐latitude oceans are still poorly documented. In this study we show through oxygen isotopes of planktonic foraminifera that thermocline waters from the Brazilian margin may have worked as a source of hydrostatic instability to return the meridional circulation to its interglacial mode. The impact of this process may have produced a colder South Atlantic thermocline during the transition to the Last Interglacial (130 kyr ago). Key Points At the onset of the Last Interglacial, δ18O of Globorotalia inflata remains close to glacial values for ~7 kyr High δ18O at the onset of the Last Interglacial can be explained by the existence of a colder and/or saltier South Atlantic thermocline A colder thermocline may have resulted from the North Atlantic heat piracy, following the resumption of deepwater convection from ~129 ka