Marília de Carvalho Campos

Centennial-scale changes in Atlantic Meridional Overturning Circulation (AMOC) strength might disturb global climate by altering interhemispheric heat transport and CO₂ partitioning between the ocean and the atmosphere. Due to the short instrumental record and lack of high-resolution paleo records that so far only resolve millennial-scale changes, centennial-scale changes remain elusive. Here we use radiocarbon ventilation ages from a western equatorial Atlantic sediment core with a remarkably high sedimentation rate to reconstruct AMOC variability during the last deglaciation, with a focus on Heinrich Stadial 1 (HS1; 17.8-14.8 ka). Results from model simulations indicate that ventilation ages serve as a sensitive proxy for AMOC variability under weak overturning conditions (i.e., during HS1) at our study location. Notably, within an overall weakened AMOC condition during HS1, our record shows two centennial-scale AMOC intensifications: one from 16.5 to 15.8 ka and another at ~15.4 ka. These centennial-scale episodes of intensified AMOC briefly revitalized Atlantic interhemispheric heat transport during HS1, resulting in decreased precipitation over northeastern Brazil and short-lived but intense changes in climate elsewhere. These episodes of AMOC intensification likely transported substantial volumes of CO₂-rich water from the mid-depth Atlantic to the Southern Ocean, where the CO₂ was rapidly outgassed to the atmosphere.

The glacial termination that occurred approximately 430 thousand years ago (i.e., Termination V) culminated in the interglacial known as Marine Isotope Stage 11 (MIS 11). During this period, Earth’s mean temperature was approximately 2°C warmer than the pre-industrial era. Therefore, it makes an excellent case study for investigating the response of key components of the climate system under global warming conditions. Warm and saline (sub)surface waters from the Indian Ocean enter the South Atlantic through its southeastern sector via the so-called Agulhas Leakage (AL), thereby influencing the heat and salt content of the basin. Variations in the intensity of the AL are thought to play a key role in modulating the strength of the Atlantic Meridional Overturning Circulation on orbital and millennial timescales. However, the scarcity of high-resolution paleoceanographic records hampers detailed investigations of AL variability during Termination V and MIS 11. Here, we assess changes in AL across this time interval based on planktonic foraminiferal assemblages, as well as Mg/Ca ratios and stable oxygen isotopic ratios of surface and subsurface planktonic foraminiferal species (i.e., Globigerinoides ruber (white) and Globorotalia truncatulinoides (sinistral)). Our results allow us to reconstruct AL faunal index, a proxy for AL intensity, and associate (sub)surface temperature and salinity changes. Altogether, the records suggest an increase in AL intensity across Termination V. Interestingly, millennial-scale subsurface signals display a delayed response of up to ~6 thousand years relative to surface conditions. Although the mechanism underlying this decoupling remain unclear, it suggests that additional processes may have influenced subsurface oceanographic variability during this key climatic interval.

Subtropical gyres contribute significantly to climate regulation by constituting the main pathways for energy redistribution between low and high latitudes. The South Atlantic Subtropical Gyre (SASG) operates in a region that is critical to the Atlantic energy balance. Its northern boundary, defined by the southern branch of the South Equatorial Current (sSEC), constitutes an important interhemispheric connection for heat and salt exchange. The sSEC bifurcates in the western tropical South Atlantic, giving rise to the Brazil Current, which transports warm and saline tropical waters southward, and the North Brazil Current, which transports heat and salt northwestward. In addition to acting as a linkage between both Atlantic subtropical gyres, the North Brazil Current constitutes an essential part of the upper branch of the Atlantic Meridional Overturning Circulation. Recently, observational data have recorded a reduction in the intensity of heat and salt transport toward the North Atlantic, along with a southward displacement of the SASG. These phenomena are likely influenced by the progressive weakening of the Atlantic Meridional Overturning Circulation, detected since the late 20th century and projected to continue in the coming decades. The lack of long-term oceanic records with adequate spatial coverage for the South Atlantic basin prevents a more complete understanding of the trends and impacts associated with SASG displacements. Here we investigate meridional changes in the position of the northern boundary of the SASG during Termination V and Marine Isotope Stage 11, through a multiproxy approach to reconstruct upper-ocean water-column stratification from a sediment core in the western tropical South Atlantic. To this end, relative abundance counts of the planktonic foraminifer species Globorotalia truncatulinoides (dextral and sinistral) and stable oxygen isotope (δ¹⁸O) analyses of G. truncatulinoides (dextral) and Globigerinoides ruber albus have been conducted. Due to the deeper apparent calcification depth of G. truncatulinoides, the difference in the δ¹⁸O signal of both species (Δδ¹⁸Otrunca-ruber) functions as an indicator of thermocline depth. The strong association of G. truncatulinoides with regions of deep thermocline allows the establishment of a relationship between variations in species abundance and changes in the stratification of the upper ocean. Since deep thermocline conditions can be interpreted as a signature of the presence of both Atlantic subtropical gyres, the proxies employed allow tracking meridional shifts in the SASG. Preliminary results are promising and suggest that the northern boundary of the SASG varied meridionally on millennial and orbital timescales. Mg/Ca ratio analyses will be performed on both species to reconstruct surface and subsurface temperatures, as well as to discriminate the individual roles of temperature and salinity in upper-ocean stratification.

The scientifically and politically agreed-upon benchmark for limiting global warming in the coming decades, as stated in the Paris Agreement, was set to “well below 2 °C above pre-industrial levels”. The interglacial period known as Marine Isotope Stage (MIS) 11, which occurred ca. 400 thousand years ago, is thought to have reached temperatures up to ~2 °C warmer than pre-industrial conditions, making it an excellent case study for investigating the behaviour of Earth’s climate under warmer-than-pre-industrial conditions.The South Atlantic is particularly important for Earth’s climate, as it represents a major heat reservoir and plays a crucial role in heat transport between the hemispheres. To better understand the behaviour of the South Atlantic under a ~2 °C warmer-than-pre-industrial climate, we are generating and compiling paleoceanographic records from the eastern and western margins of the basin spanning MIS 11 and its preceding deglaciation (Termination V). The outcomes of this research have the potential to greatly improve our understanding of South Atlantic dynamics under warmer-than-pre-industrial climates, thereby helping to constrain plausible future climate scenarios.

Luminescence emitted by minerals has long been used in paleoenvironmental studies, particularly thermoluminescence (TL) from carbonates. TL emission in calcite is controlled by the type and quantity of defects in the crystal lattice, which may act as charge traps and/or recombination centers. These defects can be influenced by environmental conditions prevailing at the time of crystallization, for example through the incorporation of impurities substituting calcium in the calcite lattice (e.g., Mg, Mn, Fe). In this context, this study investigates the potential of TL signals emitted from the calcite of the planktonic foraminifera Globigerinoides ruber (white sensu stricto, 250–350 μm) as a paleoclimate proxies. This species was selected due to its widespread use in paleoclimate reconstructions, high abundance, and known sensitivity to environmental variability. We analyzed samples from three marine sediment cores from the western Atlantic, encompassing different spatial and temporal contexts. Two cores represent modern conditions under contrasting oceanographic settings: MD23-3669MC (equatorial Atlantic) and GeoB6211-1 (subtropical South Atlantic). The third core, CDH-89 (equatorial Atlantic), spans the penultimate glacial–interglacial transition (143–122 ka), allowing the comparison between modern and paleoclimatic signal.The resulting TL intensity curves (light emitted per unit mass and unit radiation dose) exhibit peaks at approximately 65°C and 400°C. These TL signals were compared with classical paleoceanographic proxies, i.e., Mg/Ca, Mn/Ca, Fe/Ca and stable isotope data, measured on shells of the same planktonic foraminifera species. Principal component analysis indicates that the 400°C peak is primarily controlled by sea surface temperature variations, whereas the 65°C peak is associated with proxies related to continental input to the ocean. These results demonstrate that TL signals in planktonic foraminifera preserve environmental signatures, supporting their potential as new paleoclimate proxies. Further systematic testing across environments and experimental conditions is required to fully validate and advance these proxies for broader paleoenvironmental applications.

The modern rainfall regime over semiarid northeastern Brazil (NEB) is primarily controlled by the seasonal migration of the Intertropical Convergence Zone (ITCZ), with the rainy season occurring during March-April, when the ITCZ reaches its southernmost position. It is well accepted that reductions in cross-equatorial northward heat transport mediated by the Atlantic Meridional Overturning Circulation (AMOC) during abrupt cold phases of Dansgaard-Oeschger (DO) cycles, namely Greenland stadials (GS) and Heinrich stadials (HS), triggered southward migrations of the ITCZ. These migrations led to enhanced precipitation over NEB, a signal that is more clearly captured in paleoclimate records during HS.Here, we present a reconstruction of millennial-scale Atlantic ITCZ dynamics based on the longest continuous paleoprecipitation records available for NEB, spanning the last 160 thousand years (kyr) at a temporal resolution of ca. 30 years. In addition, we use numerical climate model outputs to investigate the mechanisms underlying this millennial-scale variability. The hydroclimate records are derived from a composite of iron-to-calcium (Fe/Ca) and iron-to-potassium (Fe/K) log-ratios measured in bulk sediments from marine sediment cores MD23-3670Q and MD23-3671 (1365 m water depth; 1°34.7′ S, 43°1.4′ W), retrieved offshore NEB during the AMARYLLIS-AMAGAS II cruise in 2023. High ln(Fe/Ca) and ln(Fe/K) values reflect increases in continental precipitation, which enhance chemical weathering, erosion, and terrigenous discharge to the adjacent continental margin. Our records reveal enhanced continental precipitation during cold phases (i.e., GS and HS) of the 25 DO cycles identified in the NGRIP ice core, reinforcing the strong teleconnection between tropical hydroclimate variability and high-latitude climate changes.The records further indicate consistently higher continental precipitation over NEB during HS than during GS. We show that terrigenous input (i.e., continental precipitation) is inversely related to AMOC strength (r = 0.78, p < 0.05) and to mid- to high-latitude North Atlantic sea surface temperatures (SSTs) (r = 0.9, p < 0.05). Particularly, HS are systematically associated with the highest ln(Fe/Ca) values, the weakest AMOC conditions, and the lowest North Atlantic SSTs.Numerical simulations performed with the Institut Pierre Simon Laplace climate model version 4 show a gradual increase in annual NEB rainfall as AMOC intensity is progressively reduced. This enhanced rainfall results from a gradual (i) lengthening of the rainy season over NEB and (ii) increase in mean monthly precipitation during the rainy season. The lengthening of the rainy season is driven by both a southward shift in the annual mean ITCZ position and an expansion of its southward seasonal migration range. Meanwhile, we propose that the increase in mean monthly precipitation is related to warmer SSTs in the tropical South Atlantic, which can enhance deep atmospheric convection and act as a direct moisture source for the adjacent continent. Together, these findings suggest that enhanced rainfall over NEB during North Atlantic cold events is not solely driven by a southward migration of the ITCZ, thereby advancing our understanding of tropical atmospheric dynamics during episodes of AMOC slowdown.

Previous studies have linked increased precipitation over northeastern Brazil to millennial-scale climate events, particularly Heinrich Stadials (HS), which are associated with increased freshwater input into the subpolar North Atlantic and weakening of the Atlantic Meridional Overturning Circulation (AMOC). During these intervals, reduced northward heat transport promotes a southward displacement of the Intertropical Convergence Zone, leading to enhanced precipitation over northeastern Brazil. While the atmospheric response to AMOC variability during HS is relatively well documented, the variability of ocean circulation at intermediate depths, especially in the western equatorial Atlantic (WEA), remains poorly constrained.Here, we reconstruct intermediate depth circulation and northeastern Brazil climate over the last glacial period (i.e., the last 35 ka) using marine sediment core MD23-3670Q (1ºS 43ºW; 1,357 mbsl) from the WEA. Stable carbon isotopes (δ13C) were measured in epibenthic (i.e., Cibicidoides pachyderma, C. lobatulus, C. incrassatus) and endobenthic (i.e., Uvigerina peregrina, Globobulimina affinis) foraminiferal species at a minimum resolution of 4 cm as a proxy for ventilation and carbon cycle. X-ray fluorescence (XRF) scanning performed every 1 cm provided proxies for redox conditions (i.e., ln(Mn/Ti)) and continental input (i.e., ln(Ti/Ca)).Negative δ13C excursions in epibenthic foraminifera during the Younger Dryas and HS 1, 2, and 3 suggest the accumulation of respired carbon at intermediate depths in the WEA. This interpretation is supported by the low input of terrestrial and marine organic matter to the bottom of the ocean, inferred from the small δ13C gradient between C. pachyderma and U. peregrina. In addition, neodymium isotope records from nearby core indicate only minor changes in intermediate water mass provenance throughout the last glacial period, suggesting the persistent predominance of southern sourced waters at our site. Negative C. pachyderma δ13C excursions, together with reduced ln(Mn/Ti) values during HS, indicate decreased oxygen penetration in the sediments due to a combination of reduced intermediate depth ventilation and increased sedimentation rates. A reduced δ13C gradient between C. pachyderma and G. affinis further suggests a shallower redox boundary during HS, corroborating the reduced oxygen penetration into the bottom sediments. The close correspondence between our ventilation proxies and millennial-scale variations in ln(Ti/Ca) provides evidence for ocean-atmosphere coupling between reduced intermediate water ventilation in the WEA and enhanced precipitation over northeastern Brazil, driven by changes in the AMOC strength over the last 35 ka.

Deglaciations are periods in Earth’s geological history marked by the transition from glacial to interglacial climates. Recent research has increasingly focused on identifying similarities and differences among terminations, particularly the role of millennial-scale climate variability. These transitions are marked by episodes of a weakened Atlantic Meridional Overturning Circulation (AMOC), with widespread climate impacts. Observational data suggest that the AMOC may be weakening at present due to human-induced climate change, reinforcing the importance of terminations as case studies for understanding climate behavior under reduced AMOC, global warming, global ice loss, and monsoon changes. This study compares the evolution of Terminations V (ca. 430 ka), II (ca. 135 ka), and I (ca. 20 ka) from a paleoceanographic and paleoclimatic perspective based on marine sediment cores from the western tropical Atlantic. Sea surface temperature and salinity, bottom-water ventilation, and continental precipitation over the adjacent tropical South America will be reconstructed. For this purpose, we are conducting stable oxygen and carbon isotope analyses on planktonic and benthic foraminifera, Mg/Ca analyses on planktonic foraminifera, and X-ray fluorescence analyses on bulk sediment. Our goal is to identify specific patterns of climatic variability among these terminations, focusing on regional and global ocean-atmosphere responses. These results may improve our understanding of the dynamics of rapid climate transitions and their effects on the tropical Atlantic, as well as provide insights into potential present-day climate responses to AMOC weakening. Preliminary results will be presented. [FAPESP grants 2022/06452-0, 2024/11054-9, 2024/00949-5, 2025/19613-0 and 2025/05117-0].