Two-phase amoc recovery controlled by ocean-atmospheric coupling gateway in the western South Atlantic during the last interglacial

• Ano de defesa: 2025
• Autor(a) principal: Ballalai, João Marcelo
• Orientador(a): Albuquerque, Ana Luiza Spadano
• Banca de defesa: Pivel, María Alejandra Gómez , Strikís1948, Nicolas Misailidis , Carvalho, Carla Regina Alves
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Link de acesso: https://app.uff.br/riuff/handle/1/40029
• topic: Agulhas Leakage; South Atlantic thermocline; South Atlantic subtropical gyre; Interhemispheric heat transfer; Paleoclimatologia; Variabilidade climática; Biogeoquímica marinha; Circulação oceânica global; Foraminíferos planctônicos; Aquecimento interglacial; Eventos de deglaciação; Vazamento das Agulhas; Giro subtropical do Atlântico Sul; Transferência de calor inter-hemisférica; Termoclina no Atlântico Sul

The Agulhas current retroflection process is linked to the formation of edges and filaments (Agulhas rings) through instabilities in the current, where part of these waters invades South Atlantic being incorporated into supertropical gyre (STG). The Agulhas Leakage (AL) provides an important source of density forcing the Atlantic meridional overturning circulation (AMOC) and their related waters-masses be carried towards the subpolar North Atlantic as the upper limb of the meridional circulation. The input of heat and salt throughout this route plays a key role in maintaining salinity, recovering the strength and stability of meridional circulation. The AL intensification during glacial Terminations has long been proposed as a required mechanism to return the AMOC to its interglacial mode and has a crucial role to occur the climate changes that precedes the deglaciation processes. However, the lack of records showing the downstream evolution of the AL signal and the large temporal differences between AL intensification and AMOC resumption cast doubt on this mechanism. The main objective of this study is to evaluate the extension and the role of the AL on AMOC recovery during glacial Termination II. Mg/Ca analyses were performed using ICP-OES applied in foraminiferal tests of Globorotalia inflata specie, aiming to reconstruct millenial- scale termocline paleotemperatures and paleosalinities from the western South Atlantic. During glacial Termination II, AL waters recirculated in the surface and thermocline subtropical South Atlantic until they were abruptly released to the North Atlantic in two pulses. These pulses were synchronous to two intervals of AMOC recovering recorded in 129 ka BP in the Labrador Sea, and after in 124 ka BP in the Nordic Sea during part of the Last Interglacial, both sites of North Atlantic Deep Water production. The mechanism proposed here suggests that the position of the South Equatorial current (SEC) bifurcation and the subtropical cells expansion and contraction are modulated by the Intertropical Convergence Zone (ITCZ) positioning. During glacial Terminations the ITCZ is positioned in the further southern position favoring the transport via Brazil Current, hence recirculating AL waters in the STG. At early MIS 5e the ITCZ shift to further northern positioning and favors the transport via North Brazil Current, releasing these waters toward North Atlantic. This energy partition between the northward and the southward branch of the South Atlantic western contour currents has an important role in the communication of the signal between southern and northern hemisphere and to modulate the AMOC intensity. Our hypothesis proposes connect AL intensification and the two-phase AMOC recovery during the Last Interglacial period. The SEC bifurcation acts as an ocean-atmospheric gateway controlling the northward transmission of salty anomalies from tropical regions in South Atlantic across the Equator, allowing the flux of dense AL waters to reach the sites of deep-water convection in the North Hemisphere.