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Coral‐based stable oxygen isotopes (δ18O) have been used as a proxy for sea surface temperature (SST) since the 1970s, and δ18O–SST calibration studies have been fundamental to assure robust and faithful SST reconstructions. Paleoclimatic studies based on corals from the tropical western South Atlantic (TWSA) are scarce, and the available coral species need to be calibrated to improve climate and environmental reconstructions. Siderastrea stellata, a slow‐growing coral, is a potential species to be explored as a coral archive in the TWSA. We provide the first multi‐site δ18O–SST calibration for the coral S. stellata from three locations at the TWSA: Todos os Santos Bay, Tamandaré and the Rocas Atoll. Pseudo‐coral δ18O calculations derived from gridded SSS and SST show that the contributions of SSS and SST to coral δ18O are expected to be different at each site. Weighted least squares linear regressions performed between the δ18O and SST generated the following calibrations equations: δ18O = −0.18 (±0.02) × SST (°C) + 1.90 (±0.47) for Todos os Santos Bay; δ18O = −0.18 (±0.02) × SST (°C) + 1.54 (±0.67) for Tamandaré; and δ18O = −0.16 (±0.03) × SST (°C) + 1.24 (±0.71) for the Rocas Atoll. The δ18O‐SST sensitivity of S. stellata from the TWSA is similar to that of other slow‐growing species of the genus and consistent with the expected δ18O‐SST sensitivity of other species reported in the literature. These calibrations will allow future SST reconstructions based on δ18O records from sub‐fossil and fossil S. stellata, an abundant species in the TWSA. Plain Language Summary: Corals continuously biomineralize calcium carbonate, storing environmental information within their exoskeletons in geochemical and isotopic records that span hundreds of years and making them suitable for high‐resolution climate reconstructions. The stable oxygen isotopes (δ18O) found in corals are an important proxy for revealing past sea surface temperatures (SST) and sea surface salinities (SSS). However, to ensure that this proxy is applicable to reconstruct past SST, further δ18O–SST calibration studies are needed on various regions and species. In this study, we carried out three field work experiments to provide the first multi‐site δ18O–SST calibration of the slow‐growing coral Siderastrea stellata from the western South Atlantic. Despite the slow growth nature of S. stellata corals that poses a challenge to high temporal resolution sampling, we successfully provided new calibration equations for SST reconstruction from three different locations in the western South Atlantic. Our calibration equations can now be applied to reconstruct SST based on coral δ18O records from sub‐fossil and fossil coral cores. Key Points: First multi‐site δ18O‐SST calibrations for the slow‐growing coral Siderastrea stellata from the western South Atlanticδ18O–SST sensitivity for S. stellata varied from −0.15 to −0.19‰ per °C across the different reef environmentsThis study paves the way for using S. stellata δ18O from fossil and subfossil corals for paleoclimate reconstructions from the western South Atlantic [ABSTRACT FROM AUTHOR]

Magnetic signals in deep‐sea sediments have the potential to unravel past continental environmental changes, via changes in primary terrigenous magnetic supply, but also record past marine environmental conditions, via in situ formation of secondary magnetic minerals, particularly when complemented by independent proxies. By combining environmagnetic, geochemical, and siliciclastic grain size data, we investigated marine sediment core GL‐1090 (24.92°S, 42.51°W, 2,225 m water depth) aiming to unravel changes in terrigenous sediment input and bottom water conditions during the last ∼184 ka at the western South Atlantic middepth. The Al/Si, Fe/κ and siliciclastic grain size data show that terrigenous sediments at this core location derived from the Plata River (southeastern South America). This material was transported northwards by the Brazilian Coastal Current and their delivery to our core site was modulated by sea‐level oscillations. Periods of low sea‐level were characterized by the input of coarser and more abundant terrigenous sediments. Environmagnetic parameters indicate significant downcore variations in the magnetic domain state, which we interpret as changes in the content of biogenic magnetite following glacial‐interglacial cycles. Coeval negative excursions in magnetic grain size and benthic δ13C suggests that concentrations of single domain magnetite (possibly magnetotactic bacterial magnetite) vary in response to middepth water ventilation. We suggest that reduced ventilation in the middepth western South Atlantic bottom waters during peak glaciations triggered a decrease in the production of biogenic magnetite. Peak glaciations were, in turn, linked with increases in the residence time of North Atlantic Deep Water (or its glacial counterpart). Key Points: Multi‐proxy approach points to the Plata River as the main lithogenic sediment source to tropical SE South American continental margin, modulated by sea‐levelReduced biogenic magnetite formation coeval with negative benthic δ13C anomalies during glaciationsBiogenic magnetite formation hampered by decreased bottom water ventilation during glaciations [ABSTRACT FROM AUTHOR]

The mid-Holocene (6000 calibrated years before present) is a key period in palaeoclimatology because incoming summer insolation was lower than during the late Holocene in the Southern Hemisphere, whereas the opposite happened in the Northern Hemisphere. However, the effects of the decreased austral summer insolation over South American climate have been poorly discussed by palaeodata syntheses. In addition, only a few of the regional studies have characterised the mid-Holocene climate in South America through a multiproxy approach. Here, we present a multiproxy compilation of mid-Holocene palaeoclimate data for eastern South America. We compiled 120 palaeoclimatological datasets, which were published in 84 different papers. The palaeodata analysed here suggest a water deficit scenario in the majority of eastern South America during the mid- Holocene if compared to the late Holocene, with the exception of northeastern Brazil. Low mid-Holocene austral summer insolation caused a reduced land-sea temperature contrast and hence a weakened South American monsoon system circulation. This scenario is represented by a decrease in precipitation over the South Atlantic Convergence Zone area, saltier conditions along the South American continental margin, and lower lake levels. [ABSTRACT FROM AUTHOR]