Igor Martins Venancio

This protocol describes an automated quality-control workflow for X-ray fluorescence (XRF) core-scanning data acquired using an Avaatech XRF Core Scanner. The LAM+ Core QC application validates the original Avaatech Excel workbook, performs five complementary quality-control checks, assigns a row-level Quality Flag, and generates reports for subsequent data review. The workflow evaluates instrument stability, coherent and incoherent scatter signals, local depth-related anomalies, and replicate reproducibility. The resulting Quality Flags identify measurements requiring review while preserving the distinction between acquisition quality and geochemical interpretation. The workflow is implemented in Python and is designed for reproducible processing of Avaatech XRF core-scanning datasets.

Stable carbon isotopes (δ13C) of benthic foraminifera are widely used to reconstruct past changes in deep water circulation, carbon storage, and ventilation. In addition, δ13C gradients between epifaunal and infaunal species provide insights into organic carbon export and bottom water oxygenation. However, the controls on bottom water oxygen variability in the western equatorial Atlantic (WEA) during millennial-scale climate events remain poorly constrained. Here, we investigate changes in mid-depth ventilation and oxygenation during the last glacial period using δ13C records from three benthic foraminifera (Cibicides wuellerstorfi, Uvigerina peregrina, and Globobulimina affinis). We combine species-specific δ13C records with isotopic gradients (Δδ13CU.pe–C.wu and Δδ13CC.wu–G.af), sortable silt, geochemical indicators of terrigenous input and organic carbon content. Negative δ13C excursions in C. wuellerstorfi during Heinrich Stadials (HS) indicate reduced North Atlantic Deep Water ventilation, supported by lower sortable silt values that reflect weaker bottom currents. The Δδ13CC.wu–G.af record suggests modest decreases in bottom water oxygenation during some HS, consistent with reduced ventilation and increased residence time of mid-depth waters. Although total organic carbon contents increased during HS, productivity indicators point to reduced surface productivity. Instead, higher Ti/Ca ratios and sedimentation rates indicate enhanced terrigenous input. The accumulation of terrigenous and organic material may have further limited oxygen diffusion within the sediment, influencing the δ13C signal of G. affinis. Overall, our multiproxy reconstruction indicates that HS were characterized by reduced mid-depth ventilation, weaker bottom currents, and modest decreases in bottom water oxygenation, consistent with large-scale reorganizations of the Atlantic Meridional Overturning Circulation.

The Lagoa Feia Group represents the main source rock interval in the pre-salt petroleum system of the Campos Basin, yet the controls on organic matter accumulation remain incompletely understood. This study presents an integrated geochemical investigation of 80 samples from eight wells, distributed along a proximal–distal paleobathymetric transect, combining Rock-Eval pyrolysis, LECO combustion, and XRF elemental analysis. Total Organic Carbon (TOC) ranges from 0.1% to 17.7% (mean 2.7%), with Type I–II kerogen (Hydrogen Index up to 1083 mg HC/g TOC) indicating excellent oil-prone potential. Three-component sediment decomposition (Ricken, 1993) shows that carbonate dominates mineral dilution in the Macabu (CaCO₃ = 67%) and Coqueiros (CaCO₃ = 54%) formations, while siliciclastic dilution prevails distally in the Atafona (terrigenous index up to 29%). When TOC is recalculated on a carbonate-free basis, values converge to a narrow range (5–6%) across all three formations, indicating that organic carbon flux was relatively uniform and that bulk TOC differences primarily reflect mineral dilution intensity rather than productivity. A dual dilution model was identified in which both carbonate excess and siliciclastics can dilute organic matter, depending on the depositional context. The Macabu and Coqueiros formations display significant negative CaCO₃-TOC correlations (ρ = −0.66 and −0.78, respectively), whereas Atafona shows no significant formation-level correlation (ρ = +0.2, n.s.). The Ca-TOC relationship inverts along the paleobathymetric transect: negative in proximal and intermediate wells (ρ = −0.5 and −0.7, respectively), positive in distal wells (ρ = +0.7). Maximum TOC values (~3.5–4.1%) occur in zones of compositional balance (CaCO₃ ~30–50%, TI ~20–29%). Vanadium emerges as the most robust redox proxy (ρ = +0.8), while Mn concentrations indicate that redox stability controls kerogen quality (HI = 534 for Mn < 0.2% vs 302 mg HC/g TOC for Mn > 0.3%). The proposed hierarchical model provides a predictive framework for source rock assessment in lacustrine pre-salt systems.

The rise in atmospheric CO₂ during the last deglaciation has been attributed to carbon release from the deep ocean, establishing the ocean interior as the dominant reservoir modulating glacial–interglacial CO₂ variability. In contrast, the processes by which carbon was sequestered in the ocean during periods of declining atmospheric CO₂ remain poorly constrained. In particular, three irreversible CO₂ drawdown events since the last interglacial (MIS 5d, MIS 4, and MIS 2) represent critical intervals for understanding how the ocean stored carbon over multi-millennial timescales. Here we reconstruct vertical profiles of carbonate ion concentration ([CO₃²⁻]) from deep-sea sediment records in the South Pacific, located at the junction of the Pacific and Atlantic deep-water pathways. Millennium-scale measurements of carbonate dissolution reveal distinct depth-dependent [CO₃²⁻] changes that correspond to variations in the Atlantic Meridional Overturning Circulation (AMOC) and the Antarctic Circumpolar Current (ACC). The results reveal that during periods of CO₂ drawdown, the South Pacific developed a pronounced two-layer structure, reflecting the contrasting influences of bathypelagic carbon accumulation and abyssal ventilation. By integrating our new records with existing datasets from the equatorial Pacific to Atlantic, we show that each of the three irreversible CO₂ drawdown events was characterized by carbon storage in different oceanic basins and depth ranges. These findings reveal that distinct circulation regimes of the AMOC and ACC governed deep-ocean carbon sequestration during glacial intensification, which advance our understanding of how the deep ocean regulates atmospheric CO₂.

Southern Ocean deep water mass dynamics, their interaction with the upper ocean and atmosphere in the Subantarctic Zone, are key components in Pleistocene climate change on orbital to (sub-)millennial timescales. Variations in ventilation and biogeochemical characteristics of bathyal and abyssal water masses, as well as changes in the stratification between those deep and mesopelagic waters play a major role in the marine carbon cycle and hence atmospheric CO2 concentrations on geological timescales. The realisation of IODP Expedition 383 DYNAPACC to the subantarctic South Pacific closed a critical gap in available sedimentary records from the high-latitude Southern Hemisphere, in particular for the Pacific. We use those sites in combination with piston cores from R/V Polarstern campaigns to study changes in water mass patterns and their physical and chemical signatures in the Subantarctic Zone and northern section of the ACC across the last 1.2 Ma BP. We measured benthic and planktic foraminiferal oxygen and carbon isotopes to reconstruct physical and ventilation characteristics, with one focus on Lower Circumpolar Deepwater (LCDW) at the intersection to Antarctic Bottom Water (AABW). Our results provide an abyssal δ18O and δ13C South Pacific water mass signature over last 1.4 Ma BP with with suborbital- to millennial-scale resolution, allowing to differentiate different CDW, AABW source waters and their subsequent mixing. Complementary XRF scanning-derived Zr/Rb ratios are used to relate observed variations to abyssal bottom current strength changes in the Antarctic Circumpolar Current domain. Observed offsets between Ross Sea-derived AABW and our sites imply mixing with other source waters and higher glacial isolation from proximal Antarctic bottom water sources than previously thought.Generally, glacial epibenthic δ13C minima correlate with Antarctic CIrcumpolar Current strength reductions. Suborbital- to millennial-scale δ13C changes vary in phase with atmospheric CO2 changes as recorded in the EPICA Dome C ice core back to 800 ka BP, implying a critical role of the bathyal to abyssal Pacific Southern Ocean in the Pleistocene marine carbon cycle.

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.

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.