Stability of equatorial Atlantic mid-depth circulation across the mid Pleistocene transition

• Ano de defesa: 2026
• Autor(a) principal: Costa, Luiza Freitas
• Orientador(a): Oliveira, Igor Martins Venancio Padilha de
• Banca de defesa: Kjerfve, Björn , Ramos, Rut Amelia Díaz , Nascimento, Rodrigo Azevedo
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Link de acesso: https://app.uff.br/riuff/handle/1/43299
• topic: Paleoceanography; mid-Pleistocene transition; equatorial Atlantic; stable isotopes; paleoceanografia; circulação oceânica; Atlântico equatorial; Pleistoceno Médio; isótopo estável; foraminífero bentônico; Paleoceanografia; transição do Pleistoceno Médio; Atlântico equatorial; isótopos estáveis

The mid-Pleistocene Transition (MPT, 1250 ka - 700 ka) marks the emergence of the 100-kyr-periodicity glacial cycles in the absence of significant change in orbital forcing, requiring a fundamental shift in Earth’s internal climate system. A critical weakening of the glacial Atlantic deep circulation and an increased incursion of Southern-sourced water masses between Marine Isotope Stages (MIS) 24 and 22, an event known as “Atlantic Meridional Overturning Circulation (AMOC) crisis”, has been suggested as a key driver, responsible for enhancing carbon storage, reducing pCO2 and facilitating ice-sheet growth. However, the expression of this meridional overturning disruption is not well-documented at mid-depths in the equatorial Atlantic, an important AMOC pathway. To investigate the variability of equatorial Atlantic mid-depth water masses, we used the stable carbon isotopic composition (δ13C) and oxygen isotopic composition (δ18O) from benthic foraminifera of a composite of two sediment cores (MD23-3677Q and MD23-3678), collected at the same location in the western equatorial Atlantic at 1988 m water depth. We developed an age model for the sediment cores composite based on δ18O data. We further calculated the vertical δ13C gradient to deeper sediment cores ODP 925 (also from the western equatorial Atlantic, 3052 m water depth) and DSDP 607 (from the mid-latitude North Atlantic, 3427 m water depth). Our data suggest that the proposed incursion of Southern Ocean water masses during the “AMOC crisis” event did not affect depths shallower than 2000 m water depth in the equatorial Atlantic. Moreover, no substantial changes were observed between pre- and post-MPT intervals at mid-depths in this region. The variability observed in the vertical δ13C gradients is mainly driven by deep ocean changes below 3500 m water depth, which were affected by the reorganization of the glacial Atlantic Ocean’s structure after the MPT.