This session explores the latest research results aimed at understanding the variability of tropical and subtropical South American climate and vegetation across Quaternary timescales (from glacial-interglacial, orbital, to millennial and multidecadal timescales), and the land-atmosphere-ocean interactions that control these changes. We welcome works exploring these interactions from high-resolution paleoclimatic and paleoceanographic reconstructions in (sub)tropical South American terrestrial archives (e.g. sediments, speleothems), and marine archives (e.g. sediments, corals) from the adjacent Atlantic and Pacific margins. We also invite contributions investigating Quaternary (sub)tropical South American climate and related land-ocean-atmosphere interactions based on paleoclimate modelling efforts and/or model-data comparisons.
Orals: Thu, 7 May, 16:15–18:00 | Room 0.49/50
Global warming is expected to substantially weaken the Atlantic Meridional Overturning Circulation (AMOC). However, climate models disagree greatly on the magnitude of AMOC weakening. This adds uncertainties in climate change projections, across the globe, through influencing poleward ocean and atmospheric energy transports. Here, we show through multi-model analysis of future climate change projections that AMOC weakening during this century will strongly influence precipitation and its extremes over Brazil. Such weakening dominates over the direct global warming impacts, causing drying in the Amazon, while completely mitigating them in northeast Brazil. We trace this to a tropical Atlantic warming, consistent with weakened heat transport along the southern branch of the South Equatorial Current. This induces a cross-equatorial sea surface temperature gradient and changes in latent heat flux, shifting the intertropical convergence zone southward. Our findings highlight the need to reduce uncertainties in the AMOC response to global warming and its oceanic mediated influences on Brazilian climate.
How to cite: Vilela, I., De Luca, P., Koseki, S., Silva, T., Veleda, D., and Keenlyside, N.: AMOC weakening modulates global warming impacts on precipitation over Brazil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3112, https://doi.org/10.5194/egusphere-egu26-3112, 2026.
Vegetation and fire regimes in the Neotropics have fluctuated in response to past climate oscillations, yet the drivers of these changes remain complex and regionally variable. Based on analyses of large datasets of pollen and charcoal records, we addressed how climate changes since 21 ka drove major trends of vegetation and fire changes across the Neotropics. Our findings suggest that temperature, atmospheric CO2 concentrations, and precipitation exert distinct and alternating roles as primary drivers of tree cover and fire regime changes, with additional impacts from vegetation-fire feedbacks and human activities. During the Last Glacial Maximum, tree cover in high elevation sites and at sub- and extra-tropical latitudes was mainly limited by low temperatures and reduced atmospheric CO2 concentrations, while fuel-limited conditions and/or low temperatures restrained fire activity. In the warmer tropical regions, moisture availability was likely the main controlling factor of both vegetation and fire, with the effects of low CO2 amplifying these constraints. Deglacial warming and rising CO2 promoted biomass expansion and intensified fires in temperate areas. Meanwhile, precipitation variability associated with millennial-scale events was positively correlated with tree cover and negatively correlated with fire regimes. Throughout the Holocene, relatively stable temperatures and CO2 shifted the primary control to precipitation patterns, with human activities increasingly impacting vegetation and fire regimes in the late Holocene, particularly in Central America and tropical Andes. These findings highlight the complex interplay of climate factors and anthropogenic influences shaping Neotropical ecosystems over millennia.
How to cite: Akabane, T. K., Chiessi, C. M., De Oliveira, P. E., Watling, J., Carnaval, A. C., Hanquiez, V., Bertassoli Jr., D. J., Silva, T. A., Shimizu, M. H., and Daniau, A.-L.: Climate and Human Impacts on Neotropical Vegetation and Fire Regimes since the Last Glacial Maximum, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-281, https://doi.org/10.5194/egusphere-egu26-281, 2026.
Sedimentary DNA (sedaDNA), pollen, and charcoal records from two sediment cores along the lower Negro River floodplain revealed complementary ecological and hydrological patterns throughout the Holocene in the main blackwater river located in central Amazonia. The sedaDNA record from the Lake Pacú sediment core (~9440–370 cal yr BP) provides unprecedented insight into microbial and planktonic communities across millennial-scale environmental changes. During the early Holocene (~9440–8852 cal yr BP), the presence of planktonic diatoms (Discostella nipponica, Melosira varians) and ciliates (Rimostrombidium sp., Strombidium sp.) indicate shallow, moderately productive waters with relatively low acidity compared with current Negro River conditions. A transition from ~8852 to 4520 cal yr BP is characterized by increased biological diversity compared to the early Holocene, with higher abundances and taxonomic richness of diatoms, ciliates, rotifers (Brachionus sp., Asplanchna brightwellii), and Chlorophyta (Pyramimonas tetrarhynchus). These assemblages suggest episodes of elevated nutrient input, temporary water column stratification and hydrological connectivity with surrounding floodplain environments. This interval reflects a dynamic limnological regime, with productivity fluctuating under seasonal flooding and broader hydroclimatic variability. The Late Holocene interval (~4520–370 cal yr BP) shows a pronounced ecological shift. Particularly around ~3000 cal yr BP, sedaDNA reveals the occurrence of mesotrophic diatoms, green algae, rotifers and ciliates, taxa not found under the acidic, humic waters of the Negro River. These conditions were likely driven by river connectivity, changes in water level and flow from tributaries such as the Branco River, whose chemical properties differ significantly from the Negro River. After this interval, these taxa decline toward the most recent samples, reflecting a return to more acidic, low productivity conditions similar to the river today. Complementarily, palynological data from the Apuaú River sediment core (~6450–3540 cal yr BP), a left bank tributary of the Negro River, document simultaneous expansion of Várzea type vegetation and the presence of mesotrophic diatoms (~13%), reinforcing a regional pattern of increased nutrient flux and hydrological heterogeneity during the mid- to late Holocene. Additionally, charcoal peaks dated to ~3320–2620 cal yr BP indicate intensified fire activity during the late Holocene, most likely associated with a regional dry phase rather than anthropogenic activity. Overall, our multi-proxy reconstruction of the lower Negro River provides a rare molecular record throughout the Holocene, revealing shifts in aquatic communities, vegetation and fire regimes in central Amazonia.
How to cite: Rodrigues, E. F., De Oliveira, P. E., Zhang, X., Liu, K., Yao, Q., Chiessi, C. M., Bertassoli Jr, D. J., Akabane, T. K., de Carvalho, V. A., Pessenda, L. C. R., and Liu, X.: Reconstructing Holocene floodplain ecosystems in the lower Negro River (central Amazonia) using sedaDNA, pollen, and charcoal , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1675, https://doi.org/10.5194/egusphere-egu26-1675, 2026.
The Amazon River is the largest fluvial system on Earth in terms of water and sediment discharge, exporting approximately 1.2 million tons of sediment per year to the Atlantic Ocean [1]. This flux modulates sedimentary and biogeochemical processes along the equatorial Atlantic margin and Amazon River mouth, reflecting interactions between continental, oceanic, and atmospheric processes [2]. This study evaluates three sediment cores collected at AMARYLLIS-AMAGAS II cruise (2023) in the Amazon River mouth region along a shelf–slope gradient, at water depths of 70 m (outer shelf), 696 m (upper slope), and 1696 m (mid-slope). The cores were collected using a CASQ corer and reach lengths of up to 11 meters. A multi-proxy approach was applied, including total organic carbon (TOC), inorganic carbon, calcium carbonate (CaCO₃), major and trace elements, rare earth elements (REEs) normalized to PAAS, as well as total mercury (Hg) and its stable isotopes. Geochemical ratios such as Ca/Ti, Al/Ca, and Ti/Al were used to evaluate the balance between terrigenous and carbonate components. The results indicate significant geochemical variability along the bathymetric gradient. Overall, the cores display TOC values between 1.1 - 3.3%, inorganic carbon between 1.21 - 5.81%, and CaCO₃ contents ranging from 10 to 48%. The shelf core (70 m) shows the highest variability, with CaCO₃ between 15 - 30% and fluctuations in Ca/Ti, Al/Ca, and Ti/Al ratios, reflecting hydrodynamic influence and sediment reworking. The upper slope (696 m) exhibits intermediate behaviour, with more moderate CaCO₃ contents (10–15%), indicating mixing between shelf signals and sediment transfer to deeper ocean environments. In contrast, the deeper slope core (1696 m) records a more integrated signal of sediment export and oceanic deposition, with elevated CaCO₃ contents in the upper intervals (48%), Ti/Al ratios increasing with depth, and reduced carbonate contents (< 20%), indicating enhanced terrigenous input in deeper intervals. PAAS-normalized REE patterns were parallel across all cores, indicating a relatively constant continental source consistent with the upper continental crust. The records show light to moderate enrichment of light REEs relative to heavy REEs (La/Yb 1.1), no Ce anomalies and positive Eu anomalies. Mercury isotope data show δ²⁰²Hg values between −0.9 and −1.6‰, indicating mass-dependent fractionation (MDF) dominated by light isotopes associated with terrigenous input, whereas Δ¹⁹⁹Hg (−0.35 to 0.00‰) and Δ²⁰¹Hg (−0.30 to 0.00‰) values indicate the influence of photochemical processes in the water column, such as Hg(II) photoreduction and methylmercury photodemethylation. Overall, the records suggest changes in oceanic and atmospheric processes in the Amazon River mouth influenced the sediment transport and deposition along the Amazon margin during the Quaternary.
[1] D. Feng, et al., Nat Commun 16 (2025) 3148.
[2] C.A. Nittrouer, et al., Annu. Rev. Mar. Sci. 13 (2021) 501–536.
How to cite: Santos Caldeira, G., Garnier, J., Amouroux, D., Barbieri, C., Melo Lage, M., Costa Evangelista, P., Kleindienst, A., Tessier, E., Louvat, P., and Carvalhinho Windmöller, C.: Geochemical signatures and mercury stable isotopes associated with sedimentary processes at the Amazon River mouth during the Quaternary, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15050, https://doi.org/10.5194/egusphere-egu26-15050, 2026.
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.
How to cite: Nascimento, R., Govin, A., Kageyama, M., Haut-Labourdette, M., Campos, M., and Chiessi, C.: Atlantic ITCZ dynamics during millennial-scale North Atlantic cold events, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6035, https://doi.org/10.5194/egusphere-egu26-6035, 2026.
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.
How to cite: B. Dias, B., R. Shimada, G., S. Carvalho, M., V. Montoya, T., Haut-Labourdette, M., A. Nascimento, R., Kraft, L., C. Campos, M., M. Venancio, I., P. Santos, T., V. Riveiros, N., Govin, A., and M. Chiessi, C.: Coupled changes in intermediate water ventilation and northeastern Brazil precipitation during the last glacial period, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3877, https://doi.org/10.5194/egusphere-egu26-3877, 2026.
Marine sediment cores are key archives for reconstructing past environmental conditions, including continental precipitation amount and dust flux, which are essential drivers of climate variability. Commonly, precipitation is inferred from proxies such as plant-wax hydrogen isotopes (n-alkane δD) or elemental ratios (e.g., ln(Fe/Ca)). In contrast, dust supply variability is reconstructed from aeolian mass accumulation rates or normalized-constant flux (230Th or 3HeET‐normalization) methods. Although these proxies are very powerful when the sedimentary context is favorable, they can be limited by numerous factors, including material availability, post-depositional alteration, and sea-level fluctuations. Here, we explore an alternative methodology: the study of the quartz Optically Stimulated Luminescence (OSL) sensitivity. We developed a novel luminescence scanner capable of analysing intact sediment cores without the need for subsampling. The system integrates an OSL reader equipped with infrared (850 nm) and blue (480 nm) LEDs, corresponding cutoff filters (780 nm and 420 nm), and a photomultiplier tube with an ultraviolet bandpass filter (Hoya U340). An X-ray source (60 kV) provides controlled irradiation. All components are managed by custom software, Vagalume, which enables real-time control and automatic calculation of key parameters such as BOSL₁s/BOSL_total and IRSL₁s/BOSL₁s ratios, as well as X-ray voltage and current. BOSL₁s (quartz) and IRSL₁s (feldspar) were derived from the first second of the respective decay curves, while BOSL_total was calculated from integrating the whole decay curve. These parameters allow tracking changes in terrestrial sediment sources that correlate with changes in precipitation or wind patterns. Method validation was conducted on two particularly well constrained marine sediment cores: (1) site MD23-3670Q (AMARYLLIS-AMAGAS II cruise) located off the Amazonian basin from which the Southern American monsoon precipiation amounts were reconstructed for the last 60ka and (2) site MD03-2705 (PICABIA cruise) located off West Africa from which the Saharan dust flux was reconstructed for the last 240ka (Skonieczny et al., 2019). Sediment cores were scanned at 1 cm resolution, with a 3-hour acquisition time per section (1,5m). For precipitation, the luminescence results were then compared with Fe/Ca ratios obtained via X-ray fluorescence (Avaatech) on the same sediments (MD23-3670Q). In contrast, the dust-flux estimates derived from luminescence were further compared with 230Th-normalized fluxes obtained from the same sediments (MD03-2705). Our findings demonstrate that the new scanner provides reliable, high-resolution data and represents a robust alternative for reconstructing past continental precipitation and dust flux using luminescence proxies in marine sediment archives.
How to cite: Mendes, V., Battistella, G., do Nascimento, F. J., Rojas Rocca, R., Mazur Chiessi, C., Govin, A., Skonieczny, C., Leblanc, M., Grigolato, J., Korres Bisch, V., Lika Nishimura, D., Haut-Labourdette, M., and Oliveira Sawakuchi, A.: Exploring the sensitivity of marine sediment luminescence as a new proxy for past changes in precipitation and dust supply, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21720, https://doi.org/10.5194/egusphere-egu26-21720, 2026.
In the instrumental record, eastern South America (ESA) is marked by severe droughts that triggered substantial human displacements, making it a hotspot for climate-society interactions. It is not clear, however, if past centennial-scale changes in climate like the Little Ice Age (LIA) also controlled human occupation. Here we present a precipitation reconstruction for ESA covering the last two millennia, based on the thermoluminescence sensitivity of the 110°C peak of quartz (TL sensitivity) from a marine sediment core collected off ESA. TL sensitivity serves as a proxy for sediment provenance in the region, which is controlled by rainfall patterns. Our data show that centennial-scale changes in precipitation in semi-arid northern ESA varied according to shifts in the Intertropical Convergence Zone (ITCZ). During the LIA, when the ITCZ moved southward, our core shows lower TL sensitivity values, suggesting wetter conditions over northern ESA. Importantly, these wetter intervals align with peaks in ages of archaeological remains found in the region. Concurrently, hydroclimate and archaeological records point to a drier and less populated southern ESA. Our data indicate a temporal correspondence between changes in hydroclimate and human migration from the southern to the nowadays semi-arid northern ESA. We suggest that improved environmental conditions facilitated settlement in otherwise semi-arid landscapes. By integrating marine sediment proxies and archaeological evidence, this study provides support for a climatic influence on human occupation patterns in ESA, particularly during the LIA. It also highlights the utility of luminescence-based techniques in paleoclimate reconstructions from fluvially influenced marine archives.
How to cite: Korres Bisch, V., Mazur Chiessi, C., Fonseca Giannini, P. C., Aparecida Silva, T., Bahr, A., Suarez Villagran, X., and Ribau Mendes, V.: Increased precipitation during the Little Ice Age promoted human settling in eastern South America, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-154, https://doi.org/10.5194/egusphere-egu26-154, 2026.
The Mid-Pleistocene Transition (MPT, ~1.2-0.8 Ma) marks a fundamental reorganization of Earth’s climate system, characterized by a shift from 41 kyr to 100 kyr glacial-interglacial cycles, a long-term expansion of global ice volume, and increasingly asymmetric glacial stages. This interval also witnessed widespread aridification, though the underlying drivers varied regionally: in Asia, enhanced dryness was linked to the growth of Northern Hemisphere ice sheets, whereas in Eastern Africa, more arid hydroclimate conditions were tied to a strengthened Pacific Walker Circulation. Despite the global significance of the MPT, paleoenvironmental reconstructions from Brazil are extremely limited, largely due to the scarcity of long, continuous, high-resolution sedimentary archives. As a result, the response of the western equatorial Atlantic to reorganized glacial boundary conditions remains poorly constrained, even though this region plays a key role in tropical ocean-atmosphere dynamics. To address this gap, we investigate paleoclimatic variability along the western tropical South Atlantic margin throughout the MPT and evaluate how large-scale cooling influenced regional hydroclimate and upper-ocean structure. We developed a composite sedimentary record from cores MD23-3677Q and MD23-3678 (3°14.35′S, 36°11.87′W; 1988 m water depth), recovered from a seamount off northeastern Brazil during the AMARYLLIS AMAGAS II expedition. Planktonic foraminiferal geochemistry (δ13C, δ18O and Mg/Ca ratios) was measured in Globigerinoides ruber and Neogloboquadrina dutertrei at 4-cm resolution to reconstruct sea-surface temperatures, atmosphere–ocean coupling, and upper-ocean stratification through the MPT. Ongoing analyses will provide new constraints on tropical hydroclimate variability, SST changes, and the evolution of upper-ocean structure in the western equatorial Atlantic, offering fresh insight into how low-latitude feedbacks evolved under progressively cooler global climates during the MPT.
How to cite: Pedrazzi-Chacon, A. B., Venancio, I., Freitas, L., Riveiros, N., Albuquerque, A. L., Chiessi, C., and Govin, A.: Upper-ocean variability in the Equatorial Atlantic across the Mid-Pleistocene Transition, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1091, https://doi.org/10.5194/egusphere-egu26-1091, 2026.
Several paleoclimate studies focus on the impacts of changes in Atlantic Meridional Overturning Circulation (AMOC) on the dynamics of the South American Monsoon System (SAMS) on millennial timescales; however, they lack interpretations on longer timescales throughout the Quaternary. Here, we present a sediment core covering the last 1 million years collected in the tropical region of the eastern Brazilian margin near the São Francisco River mouth. We used the ln(Si/Al) as hydroclimate proxy, interpreting as changes in the SAMS activity, and also δ13C of benthic foraminifera to track changes on deep-water circulation. We observed substantial changes between 700-400 ka, marked by the weakening of the SAMS simultaneously with increasing long-term trend of δ13C, suggesting a coupled ocean-atmosphere changes during this period. We infer that the observed increase in ventilation is a response to a stronger AMOC, which leads to a global northward migration of the Intertropical Convergence Zone (ITCZ), resulting in a decrease in SAMS intensity. Thus, our data offer insights into long-term coupled responses between the oceanic and atmospheric systems in the tropical realm during the Quaternary.
How to cite: Gomes, B., Venancio, I., Ballalai, J., Figueiredo, T., de Almeida, A., and Albuquerque, A. L.: Eastern Brazil Hydroclimate Weakening Linked to Stronger AMOC During the Pleistocene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-103, https://doi.org/10.5194/egusphere-egu26-103, 2026.
The mid-Pleistocene Transition (1.25-0.7 Ma) marks the emergence of the 100-kyr-periodicity and more intense glacial cycles without changes in orbital forcing, requiring a fundamental shift in Earth’s internal climate system. A critical glacial Atlantic deep circulation weakening and increased Southern Ocean water masses incursion between MIS 24 – MIS 22, even during the interglacial MIS 23, has been suggested as a key driver, responsible for enhancing carbon storage, reducing atmospheric CO2 and facilitating ice-sheet growth, and has been called as “AMOC crisis” event. However, the expression of this thermohaline disruption is not well-documented at intermediate depths in the Equatorial Atlantic, an important AMOC flow branch. To investigate the Equatorial Atlantic mid-depth water masses variability across the MPT, we applied a benthic foraminiferal δ13C record from a two-core composite MD23-3677Q (1988 m) and MD23-3678 (1988 m), positioned in the NADW upper layer. We built two vertical gradients (Δδ13C) between our record and two published data from deeper cores (DSDP 607 and ODP 925), influenced by the NADW deep layer. A close-to-zero Δδ13C indicates the same water mass influence at mid-depth and deep ocean. Our data suggests that the proposed Southern Ocean water masses incursion and expansion across the AMOC crisis event did not affect depths shallower than 2000 m. Moreover, no substantial changes were observed between intervals pre- and post-MPT at intermediate depths in the Equatorial Atlantic, and the variability observed in the vertical gradients is mainly driven by deep ocean changes, which were affected by the reorganization of the glacial Atlantic Ocean structure after the MPT.
How to cite: Freitas, L., Venancio, I., Santos, T., Pedrazzi-Chacon, A. B., Skonieczny, C., Vázquez Riveiros, N., Spadano Albuquerque, A. L., Govin, A., and Chiessi, C.: Stability of the Equatorial Atlantic mid-depth circulation across the mid-Pleistocene transition, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-104, https://doi.org/10.5194/egusphere-egu26-104, 2026.
The deep ocean circulation during the last glacial cycle exhibited characteristics distinct from the Holocene. This interval marks the transition between glacial and interglacial conditions, strongly influenced by millennial-scale Heinrich events, which were characterized by massive iceberg discharges into the North Atlantic. Studies indicate that during these events, the AMOC became shallower and weaker, resulting in a pronounced reduction in deep ocean circulation across the Atlantic. In this study, we present three sediment cores: DGL-1914 (1131 m), DGL-1905 (2513 m) and DGL-1903 (2704 m), collected along the western Brazilian margin near the São Francisco River, spanning the last 40.000 years. To investigate variability in deep-current velocity, we applied the Sortable Silt proxy in combination with the Zr/Rb ratio, both indicators of paleocurrent strength. Our results show that during Heinrich events (H1, H2, H3, and H4), significant changes occurred in current velocities, reflecting distinct hydrodynamic conditions associated with the Intermediate Western Boundary Current (IWBC) (core DGL-1914) and the Deep Western Boundary Current (DWBC) (cores DGL-1905 and DGL-1903). In particular, we observe a pronounced reduction in the DWBC flow during these events, indicating a weakening of the AMOC in the South Atlantic throughout these intervals. These results provide new insights into deep circulation in the western South Atlantic and contribute to a more comprehensive understanding of bottom-waters dynamics along the Brazilian margin.
How to cite: Tayt-Sohn, R., Venancio, I., Ballalai, J., Figueiredo, T., de Almeida, A., and Albuquerque, A. L.: Reconstructing bottom currents along the Brazilian margin from the Last Glacial Maximum to the Holocene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-384, https://doi.org/10.5194/egusphere-egu26-384, 2026.
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].
How to cite: Kraft, L., C. Campos, M., Q. P. Turman, V., L. Campese, T., S. Marques, B., B. Dias, B., A. Nascimento, R., A. Hartmann, G., Govin, A., and M. Chiessi, C.: Late Quaternary deglaciations in the western tropical Atlantic and eastern tropical South AmericaLate Quaternary deglaciations in the western tropical Atlantic and eastern tropical South America, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-761, https://doi.org/10.5194/egusphere-egu26-761, 2026.
As the largest drainage in the world, the Amazon River basin shows intricate and only partially known responses to hydroclimate changes linked to atmospheric reorganization and/or the strength of the Atlantic Meridional Overturning Circulation (AMOC). Many of the hydroclimatic reconstructions for the region were obtained from speleothems, often representing limited local characteristics. Thus, tracking the source of siliciclastic sediments deposited off northeastern South America is particularly well suited to understanding how precipitation in different sectors of the basin may have responded to distinct climate and ocean circulation states. Here we present a high-resolution multi-proxy approach to determine the provenance of the sediments deposited off the Amazon River mouth since the Last Glacial Maximum (LGM) using radiogenic Nd isotopes on clay-size detrital fractions, bulk-sediment major elemental ratios (e.g., Fe/K, Fe/Ca, and Al/K), and quartz optically stimulated luminescence (OSL) sensitivity. We applied these proxies to marine sediment core GL-1251 (1°04.1' N, 45°48.0' W, 2.596 m water depth), the most proximal core to the Amazon River mouth ever studied, making it an excellent archive to address this subject. The new data presented here shows that during the (i) LGM, the (ii) Bølling–Allerød and the (iii) Younger Dryas (YD), deposition at our core site was dominated by sediments transported directly by the Amazon River. During these periods, Andean material dominated the siliciclastic fraction, and fluvial sediment discharge into our core site was favored by relatively low sea level. Our εNd data suggest an abrupt increase in the contribution of the Solimões catchment (northern Central Andes) at the expense of the Madeira catchment (southern Central Andes) during the late YD. However, we identify two periods during which cratonic sources dominated the siliciclastic fraction. The first and most prominent occurred during Heinrich stadial 1 (HS1), and the second during the early to mid-Holocene. During HS1, we argue that, despite enhanced Amazon River freshwater discharge caused by increased precipitation over the Amazon basin, relatively few Andean-derived sediments were deposited at the GL-1251 site. This could be explained by a reduction in the strength of the North Brazilian Current (NBC) towards the northwest, which, in turn, depends on the control of the AMOC. In contrast, the massive intensification of precipitation over eastern Amazon and northeastern Brazil substantially increased cratonic sediment input from catchments draining the Brazilian Shield, resulting in high sedimentation rates. During the early Holocene, we propose that sea-level rise was accompanied by predominant transport of the Amazon sediment plume in the northwestern portion of the Amazon shelf, allowing sustained sediment input from rivers draining the Brazilian Shield at the site of GL-1251. Overall, our data indicate markedly changing precipitation patterns over tropical South America since the LGM, which affected the source of siliciclastic sediments deposited on the northeastern continental margin of South America and possibly imply direct linkage with abrupt changes in the strength of AMOC.
How to cite: Hamada Magalhães, R., Chiessi, C., Pereira dos Santos, T., Venancio, I., Ribau Mendes, V., Oliveira Sawakuchi, A., Grigolato, J., Albuquerque, A. L., and Bayon, G.: AMOC-driven shifts in Amazon sediment sources since the Last Glacial Maximum, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7217, https://doi.org/10.5194/egusphere-egu26-7217, 2026.
The Amazon basin is one of the most influential hydroclimatic systems on the planet, modulating the water cycle and energy balance of the tropical regions. The long-term stability of the Amazon rainforest is closely linked to regional hydroclimate, as shifts in rainfall amount and seasonality can drive substantial ecological transformations across the basin. Understanding how the Amazon system has naturally responded to past oceanic and atmospheric forcings is crucial, and paleoclimate records provide information to investigate the mechanisms governing Amazonian hydroclimate variability through time. Yet, paleoclimate archives that allow us to explore its variability beyond the last 50 ka are limited. The objective of this study is to characterize orbital- and millennial-scale hydroclimatic changes within the Amazon basin over the last 220,000 years through high-resolution X-ray fluorescence (XRF) analysis on marine sediment cores recovered from the northern margin of French Guyana during the AMARYLLIS–AMAGAS II cruise, specifically at stations S6 and S7 where a composite record was produced for each station by combining cores MD23-3652Q/53 and MD23-3655Q/56, respectively.
XRF results of S6 cores, which have an age model, allowed us to associate geochemical changes with Marine Isotopic Stages (MIS 1–7) and Heinrich Stadials of the last 60 ka. High values of Fe/Ca and Al/K log-ratios are observed during Heinrich Stadials (HS1–H6), indicating increased input of terrigenous vs. biogenic material, consistent with enhanced fluvial discharge, and an enhanced contribution of chemically weathered material from the Amazon basin. Elevated ln(Fe/K) and ln(Al/K) ratios specifically suggest a stronger contribution from lowland, highly leached soils and enhanced precipitation-driven weathering within the basin, rather than changes in sediment provenance. These patterns suggest globally wetter conditions over the Amazon Basin during HS, in agreement with the documented southward shift of the Intertropical Convergence Zone (ITCZ) and strengthening of the South American monsoon. During interglacial periods such as MIS 5e and MIS 1, higher sea levels likely reduced the continental influence on sedimentation at the core sites, enhancing the relative contribution of marine carbonates. This is reflected by lower ln(Fe/Ca) and ln(Fe/K) ratios, together with higher ln(Sr/Ca) values, which indicate a decline in terrigenous input and a stronger oceanic influence. During glacial stages (MIS 6, 4 and 2), the combination of high ln(Fe/Ca) and an increased ln(Al/K), denotes intensified fluvial supply and stronger chemical weathering under humid conditions, despite lowered sea level.
S7 cores, although lacking an age model, allow for a qualitative comparison due to their geographic proximity to S6. The general trends in Fe/Ca and Al/K log-ratios are consistent with those of S6, suggesting that S7 cores record the same regional signal of Amazonian fluvial variability, modulated by the tropical hydroclimatic regime. These preliminary results demonstrate that XRF records from S6 and S7 cores constitute an exceptional archive for evaluating the interaction between the Amazonian hydroclimatic system and North Atlantic forcings, indicating that during Heinrich Stadials, a southward migration of the ITCZ and intensified tropical rainfall enhanced Amazonian river discharge and continental runoff.
How to cite: Benitez Frometa, P., Govin, A., Herve, G., Grigolato, J., Azebedo Nascimento, R., and Mazur Chiessi, C.: Natural variability of the Amazonian hydroclimate over the last two glacial cycles (220,000 years)., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6411, https://doi.org/10.5194/egusphere-egu26-6411, 2026.
The Amazon rainforest is a key component of the South American climate system, with strong vegetation-convection feedback and a tight coupling with large-scale atmospheric circulation. However, the relative roles of abrupt millennial-scale climate events and orbital forcing in modulating Amazon Basin hydroclimate remain incompletely understood over long timescales. Indeed, most available records either cover short time windows or come from distal sites where Amazonian signals may be diluted by non-local influences. Here, we reconstruct precipitation variability over the Amazon Basin during the last 200 kyr using the composite marine sediment core MD23-3652Q-53, recovered from the mid-depth western equatorial Atlantic and directly influenced by Amazon River discharge. First, we produced a detailed age model for the composite core based on nine calibrated radiocarbon ages and 511 benthic foraminifera stable oxygen isotope values. Second, we assessed changes in continental runoff and precipitation based on X-ray fluorescence elemental ratios and sediment reflectance data. Third, we determined the timing of millennial-scale changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) based on benthic foraminifera stable carbon isotope (d13C). Lower δ13C values during millennial-scale events coincide with increased ln(Ti/Ca) ratios and higher L* reflectance, indicating a reduction in North Atlantic Deep-Water ventilation and enhanced terrigenous sediment supply to the western equatorial Atlantic. These hydroclimate changes are consistent with a weakened AMOC, which promoted interhemispheric temperature asymmetry, a southward displacement of the Intertropical Convergence Zone, and strengthened of Amazonian precipitation. In contrast, higher a* reflectance values could be associated with periods of increased austral summer insolation, likely reflecting orbitally-driven changes in terrigenous sediment composition, primarily linked to enhanced precipitation over the Andean headwaters. These findings highlight the response of the Amazon hydrological system to distinct modes of climate forcing and provide important constraints on the sensitivity of tropical South American precipitation to future changes in the AMOC.
How to cite: Grigolato, J., Mazur Chiessi, C., Borba Dias, B., Pereira dos Santos, T., Valloto Silva, L., Teixeira Alves, J., Almeida Leonetti, M., Crivellari, S., Azevedo Nascimento, R., Hamada Magalhães, R., Benitez, P., and Govin, A.: Millennial and orbital-scale variability of Amazon Basin precipitation over the last 200 kyr, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5684, https://doi.org/10.5194/egusphere-egu26-5684, 2026.
Changes in Amazonian hydrology and vegetation strongly influence global geochemical and hydrological cycles. In particular, the vast Amazon floodplains are a major source of atmospheric methane (CH₄), so variations in their extent can substantially impact the global methane budget. Understanding how these floodplains responded to past climate change, especially during periods prior to dominant anthropogenic influence, is therefore critical for constraining natural methane–climate feedbacks and their role in global climate dynamics.
Here, we investigate past vegetation and hydroclimate changes in lowland Amazonia using organic geochemical proxies from a marine sediment core offshore the Amazon River. The δD and δ¹³C signatures of long-chain n-alkanes provide information on past rainfall and vegetation dynamics, while bacteriohopanepolyol (BHP) biomarkers are used to reconstruct variations in the extent of terrestrial wetlands. We assess how climatic and environmental differences between the Holocene and earlier interglacials, particularly the Last Interglacial, influenced the expansion and contraction of Amazonian floodplains. In particular, we aim to test the hypothesis that differences in orbital-scale insolation between these periods contributed to divergent Glacial–Interglacial methane emission patterns. Funding provided by FAPESP (22/06440-1, 23/15362-7, and 25/09149-4).
Keywords: organic geochemistry, paleoclimatology, Amazon
How to cite: Melo, D., Lipp, J., Schefuß, E., Chiessi, C., Sawakuchi, A., and Bertassoli, D.: Climate–Floodplain Interactions in the Amazon Basin Revealed by Organic Geochemical Proxies , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19837, https://doi.org/10.5194/egusphere-egu26-19837, 2026.
During the penultimate deglaciation, which largely coincided with Heinrich Stadial 11 (HS-11, ~136-129 ka), meltwater pulses cooled the North Atlantic and weakened the Atlantic Meridional Overturning Circulation (AMOC), driving a southward shift of the Intertropical Convergence Zone (ITCZ) and arid conditions in northern South America. Although deglacial effects persisted for several millennia into the subsequent Last Interglacial period (LIG, ~129-115 ka), the response of the ITCZ to this transitional climate state remains poorly constrained. Here, we present paleoenvironmental records from a marine sediment core north of the Orinoco River delta, where runoff-sensitive proxies track northern South American rainfall and Atlantic ITCZ migration, and benthic δ¹³C records indicate AMOC strength. Our records show a gradual increase in precipitation during the early LIG, indicating a progressive northward migration of the ITCZ. Notably, the onset of peak wet conditions at 126.5±1 ka coincides with stabilized benthic δ¹³C values, consistent with the re-establishment of a fully developed interglacial AMOC. This temporal alignment suggests that the lingering effects of the penultimate deglaciation, such as gradual cessation of freshwater influence, subpolar North Atlantic SST warming and AMOC recovery, played an important role in shaping tropical hydroclimate during the first 4 millennia of the LIG, and should be incorporated in climate models.
How to cite: Zhuravleva, A., Mohtadi, M., Hines, S. K. V., Costa, K. M., Fahl, K., Kienast, M., and Bauch, H. A.: Legacy of Northern Hemisphere deglaciation on Tropical Rainbelt Migration during the Early Last Interglacial Period, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16941, https://doi.org/10.5194/egusphere-egu26-16941, 2026.
During Heinrich Stadial 1 (HS1), δ13C decreased throughout most of the upper North Atlantic between∼ 1000 – 2500 m, and in some deeper South Atlantic sites. Most studies explain the δ13C decrease as a response to a weakening of the Atlantic circulation, but the origin and pathway of this poorly-ventilated water mass is still debated. The behavior of intermediate and deep waters during previous Heinrich Stadials is even less well constrained. Here, high-resolution records of the last 45 ka from marine sediment cores off the Brazilian margin are compared with freshwater forcing simulations of the Earth System Model of intermediate complexity iLOVECLIM, using δ18O as a water mass tracer. Our data reveal a low-δ13C water mass at 2300 m during the last four HS. HS1 and HS4 are also marked by decreases in benthic foraminifer δ18O too large to be due to sea level changes alone, suggesting the incursion of warmer and/or fresher waters between 2300 - 3600 m. Model simulations indicate the presence of a southward-flowing, low-δ18O water mass spreading from the North Atlantic to the tropics, likely transported by the Western Boundary Current. Our results thus suggest that the minimum in ventilation in the Tropics during HS is of northern origin, rather than being related to an expansion of southern waters to shallower depths.
How to cite: Vazquez Riveiros, N., Waelbroeck, C., Roche, D., Moreira, S., Burckel, P., Dewilde, F., Skinner, L., Arz, H., Boehm, E., and Dokken, T.: Ventilation decreases during Heinrich stadials in the deep water masses of the western tropical Atlantic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7767, https://doi.org/10.5194/egusphere-egu26-7767, 2026.
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.
How to cite: Q. P. Turman, V., C. Campos, M., B. Dias, B., A. Nascimento, R., M. L. Pinho, T., L. Campese, T., S. Marques, B., Kraft, L., Hartmann, G., M. Venâncio, I., L. S. Albuquerque, A., M. Ballalai, J., G. Almeida, A., and M.Chiessi, C.: Meridional shifts in the northern boundary of the South Atlantic Subtropical Gyre during Termination V and MIS 11: a multiproxy approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8237, https://doi.org/10.5194/egusphere-egu26-8237, 2026.
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.
How to cite: Campos, M., Kraft, L., Marques, B., Campese, T., Turman, V., Dias, B., Nascimento, R., Hartmann, G., and Chiessi, C.: Reconstructing South Atlantic climate during MIS 11 and Termination V, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5796, https://doi.org/10.5194/egusphere-egu26-5796, 2026.
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.
How to cite: S. Marques, B., C. Campos, M., A. Nascimento, R., B. Dias, B., P. Santos, T., M. Chiessi, C., L. Campese, T., Q. P. Turman, V., Kraft, L., A. Hartmann, G., M. L. Pinho, T., V. L. Kochhann, M., J. F. Meier, K., Hemming, S., Hall, I., and Bahr, A.: Surface and subsurface Agulhas Leakage dynamics across Termination V and MIS 11, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8413, https://doi.org/10.5194/egusphere-egu26-8413, 2026.
Climate variability during the end of the Pleistocene and the Holocene has been widely investigated in tropical South America, where precipitation is primarily controlled by the South American Summer Monsoon. Despite numerous regional syntheses, the existence and role of an east-west tropical South American precipitation dipole remain debated.
Here we present a new paleo-hydrological record from Laguna Larga, a ria lake located in the Llanos de Moxos (Bolivian lowlands). We analyse plant-wax n-alkanes and their hydrogen and carbon stable isotopes, together with portable XRF elemental data, to reconstruct hydroclimate, vegetation and erosion changes in the southwestern margin of the Amazon rainforest over the last 13 kyr BP.
Our results reveal hydrological fluctuations that influenced catchment vegetation. These variations highlight the dominant role of precipitation in shaping seasonally flooded savannahs such as the Llanos de Moxos, with implications for land cover dynamics, biodiversity, and human occupation.
This record provides new insights into late Quaternary rainfall variability in southwestern Amazonia and contributes to the ongoing discussion on large-scale precipitation patterns into tropical South America.
How to cite: Manzella, G., Butiseacă, G.-A., Schefuß, E., and Lombardo, U.: Assessing late Quaternary paleohydrology in the Bolivian Amazon through plant waxes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18850, https://doi.org/10.5194/egusphere-egu26-18850, 2026.
The climate of Northeastern Brazil is strongly controlled by the latitudinal migrations and intensity of the intertropical convergence zone (ITCZ), which govern the spatial and temporal distribution of precipitation and, in turn, vegetation and faunal resources that have been critical for human populations. However, the long-term interactions between ITCZ variability, climate and ecosystems are still poorly understood. Here we present a new record based on molecular biomarkers and their isotopic composition documenting the evolution of paleoenvironments in Northeastern Brazil during the last deglaciation.
Sixty samples were collected from the MD23-3670Q core retrieved off the Parnaíba delta during the AMARYLLIS-AMAGASII campaign. Concentrations and carbon isotopic composition (δ13C) of molecular biomarkers (n-alkanes, fatty acids, and pentacyclic triterpenes) were determined to reconstruct climate and vegetation dynamics over the 8.9 to 22.2 cal kBP period.
The δ13C record of n-C26 fatty acid shows similar variations as those of bulk organic matter (OM) δ13C, with an average -6‰ offset. This offset increases during the Bølling-Allerød and Preboreal, reflecting enhanced contributions of marine-derived OM and less terrestrial-derived OM. As a matter of fact, fatty acid δ13C values indicate a stronger contribution of C4-vegetation, suggesting drier conditions, during this period. Reversely, lower δ13C values indicate a stronger contribution of C3 vegetation, consistent with wetter conditions, during the Heinrich Stadial 1 and the Younger Dryas. Surprisingly, the Average Chain Length of fatty acids suggests reverse interpretation. Gramineae-specific biomarkers are abundant during the Heinrich Stadial 1 but rare during the Younger Dryas although climatic conditions appear close. High levels of Asteraceae biomarkers are abundant during both Heinrich Stadial 1 and Younger Dryas. Finally, taraxerol levels are notable during two episodes included in the Younger Dryas. This might reflect two phases of conditions favorable for the development of mangroves during sea level rise.
Together, these results reveal a complex and sometimes decoupled response of vegetation and coastal ecosystems to deglacial climate variability in Northeastern Brazil, emphasizing the combined influence of ITCZ-driven hydroclimate changes, sea-level fluctuations, and non-linear response of NE Brazil vegetation to climate changes.
We are grateful to the crew of the R/V Marion Dufresne and GENAVIR staff members for their help in collecting AMARYLLIS-AMAGAS II cores. We also acknowledge the Brazilian Navy and the Brazilian National Council for Scientific and Technological Development (CNPq) for granting access to collect and investigate the material taken in Brazilian jurisdictional waters during the AMARYLLIS- AMAGAS II cruise (ANR 17-EURE-0006).
This research was supported by the project ANR SESAME “Human paleoecology, Social and cultural Evolutions among first Settlements in Southern America (ANR 20-CE03-0005).
How to cite: Pioggini, O., Jacob, J., Hatté, C., Dejean, I., Riausset, S., Gauthier, C., Govin, A., and Chiessi, C.: Climate and vegetation dynamics during the last deglaciation in Northeastern Brazil inferred from molecular biomarkers and their isotopic composition, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19453, https://doi.org/10.5194/egusphere-egu26-19453, 2026.
Northeastern Brazil (NEB) is one of the most hydroclimatically sensitive regions in South America. Its globally semi-arid hydroclimate is shaped by the seasonal migration of the Intertropical Convergence Zone (ITCZ). Paleoclimate records documented a southward shift of the mean ITCZ position and intensified precipitation over NEB during millennial-scale events, which mobilized large quantities of detrital material transported to the adjacent Atlantic margin.
Environmental magnetism offers a non-destructive, high-resolution approach to assess the sediment provenance, weathering intensity, and mineralogical transformations. Magnetic minerals such as magnetite, hematite, and goethite carry unique coercivity and thermal signatures that reflect their formation and transport history. Few paleoclimate studies showed an increase in high-coercivity minerals in NEB marine sediments during past millennial-scale events, which may reflect enhanced riverine input from intensely weathered continental regions. However, the interpretation of magnetic records is limited by the absence of modern reference datasets from upstream continental sources.
Here we provide the first comprehensive rock-magnetic characterization of modern NEB continental sediments to better trace their provenance and improve the paleoclimatic interpretation of magnetic records in marine sediment cores. We investigated the magnetic mineralogy of about 80 modern sediment samples collected within the Parnaíba and the Maranhão hydrological systems using a suite of environmental magnetic techniques, which includes the acquisition and demagnetization of the Natural, Anhysteretic and Isothermal remanent magnetizations (NRM, ARM, IRM), stepwise thermal demagnetization of 3-axes IRM, hysteresis loops, backfield IRM curves with unmixing of coercivity spectra and thermomagnetic curves.
First results highlight the diversity of modern magnetic signatures within the Parnaíba and the Maranhão basins. Different mixing proportions of low-coercivity minerals such as magnetite versus high-coercivity minerals such as hematite and goethite seem to reflect contrasting source conditions within NEB in terms of rainfall amount, weathering intensity and lithology. In addition, while samples dominated by magnetite are abundant in regions with a crystalline bedrock and in downstream areas close to river mouths, samples with a high proportion of high-coercivity minerals (hematite, goethite) dominate in upstream NEB regions. Therefore, a grain-size sorting process may also be at play along the Parnaíba and the Maranhão hydrological systems and contribute to explain the spatial differences in modern magnetic mineralogy observed within NEB.
How to cite: Govin, A., Alam, S., Gwenaël, H., Wandres, C., Van Toer, A., Ledru, M.-P., Mendes, V. R., and Chiessi, C. M.: Magnetic fingerprinting of modern continental sediments in Northeastern Brazil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11608, https://doi.org/10.5194/egusphere-egu26-11608, 2026.
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.
How to cite: Campese, T. D. L., Campos, M. D. C., Ortiz, C., Dias, B. B., Chiessi, C. M., Marques, B. D. S., Kraft, L., Turman, V. Q. P., Hartmann, G., Radionovskaya, S., Skinner, L., Govin, A., Mendes, V. R., Mineli, T. D., Bahr, A., Mulitza, S., and Sawakuchi, A. O.: Planktonic foraminifera luminescence as a new paleoclimate proxy for oceanic and atmospheric conditions off South America, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-835, https://doi.org/10.5194/egusphere-egu26-835, 2026.
There are several natural climate archives where proxies can be applied to retrieve information about changes in vegetation, soil and water temperature, continental rainfall regimes, as well as variations in sea surface salinity and temperature. Among these records, stalagmites and corals stand out for their high temporal resolution: the former allow the reconstruction of continental precipitation variations, while the latter enable the identification of changes in marine temperature and salinity. Both are predominantly composed of calcium carbonate (CaCO₃), and generally their proxies comprehend isotopic analyses of carbon and oxygen, as well as magnesium-to-calcium ratios. Given the importance of understanding climate fluctuations in continental and marine environments, the development of new analytical methods to improve the interpretation of these records is essential. In this context, luminescence techniques (Optically Stimulated Luminescence (OSL), Fluorescence, and Phosphorescence) have proven to be promising tools, as they allow the establishment of correlations between luminescent signals and environmental variables such as temperature, precipitation, and salinity. Although the use of OSL is already well established for dating minerals such as quartz and feldspar, its application to carbonate materials as proxies for environmental changes is still recent and under development, while the study of fluorescence and phosphorescence in these materials remains little explored. The development of the first luminescence scanner dedicated to measuring carbonates enabled high-resolution testing of these emissions, specifically in stalagmites and corals. Measurements were performed continuously, at a constant speed of 100 mm/min, along the main growth axis of the stalagmites and from the top to the base of the corals. The experimental protocol was designed to assess temporal variations and consisted of five main steps: (1) X-ray irradiation (40 kV, 300 µA, 100 mm/min); (2) signal reading with LEDs turned off (11x); (3) IRSL signal reading (3x); (4) BOSL signal reading (5x); and (5) signal reading with LEDs turned off (2x). The tests revealed a strong correlation between the blue-light fluorescence signal and oxygen isotopes (ẟ¹⁸O) in the stalagmites, whereas in the coral samples, a greater similarity was observed between the blue-light fluorescence signal and carbon isotopes (ẟ¹³C). Furthermore, the decay tests showed no signal loss over time, suggesting that the stalagmites emit not only optically stimulated luminescence but also fluorescence and phosphorescence. These results demonstrate the potential of the technique not only for detecting quartz and feldspar grains trapped within carbonate matrices but also for investigating intrinsic properties of calcium carbonate itself, opening new perspectives for high-resolution paleoclimate studies. The newly developed equipment enables rapid sequential analyses, thus representing an excellent alternative for material screening. Due to its low cost per analysis, it will be possible to examine a wide range of samples, which constitutes a significant advantage over conventional, well-known methods, typically more expensive and time-consuming.
How to cite: de Carvalho Gradwohl, R., Battistella, G., J. Nascimento, F., W. C. Junior, F., M. Strikis, N., S. Pereira, N., and R. Mendes, V.: Advancing Paleoclimate Proxies: Insights from a Novel Luminescence Scanner Applied to Stalagmites and Corals, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-216, https://doi.org/10.5194/egusphere-egu26-216, 2026.
