In this study, we associated the variations in coccolithophore assemblages with the variability in major elements (Fe, Ca, and Ti) from the continental slope of the western South Atlantic by investigating two marine sediment cores (GL-824 and GL-1109) to reconstruct paleoceanographic and paleoproductivity changes from the Last Glacial Maximum (LGM) to the present. Terrigenous-supply proxies (Fe/Ca and Ti/Ca) showed a very similar pattern compared with the fine-fraction sediments, higher values throughout the LGM and lower values during the Holocene. The dominant species in the coccolithophore assemblages were Emiliania huxleyi, Gephyrocapsa spp., and Florisphaera profunda, with these species together representing between 82 and 99% of the total assemblage. Additionally, we used three other subordinate species (Umbellosphaera ssp., Rhabdosphaera spp., and Syracosphaera spp.) for paleoproductivity reconstruction. The estimates of primary production using F. profunda and Gephyrocapsa spp. exhibited a similar trend, with higher productivity values during the LGM. Paleoproductivity decreased toward the Late Holocene. Analyzing these results, we observed that the oscillation of relative sea level was the process that controlled paleoproductivity, primarily by changing the position of the main flow of the Brazil Current (BC). During periods of high sea level (low Fe/Ca and Ti/Ca), the BC transported warm and oligotrophic water to the upper slope, preventing any nutrient transport from deeper layers or coastal water. In contrast, during low sea-level periods (high Fe/Ca and Ti/Ca), the offshore displacement of the BC allowed the presence of coastal water (more nutrient-rich than tropical water) and the erosion of the exposed shelf that along with a more enhanced fluvial input provided more nutrients to the photic zone, thus enhancing primary productivity.

Element and mineral associations are fundamental parameters for palaeoceanographical reconstructions but laboratory methodologies are expensive, time-consuming and need a lot of material. Here, we investigate the quality and reliability of XRF measurements of major elements (Fe, Ti and Ca) using BTX II Benchtop, by comparing them with previous ICP-OES elemental analysis for a set of Late Pleistocene marine sediments from Campos Basin. Although the numerical values of the logarithmic form of the elementary ratios were different, the lnTi/Ca and lnFe/Ca ratios measured by both techniques (XRF and ICP-OES) presented similar downcore results. To correct the XRF intensity data, a linear regression model was calculated and, based on the linear equation generated, the logarithmic values of the elementary XRF ratios were corrected. After the correction, One-Sample t-test and Bland–Altman plot show that both techniques obtained similar results. In addition, a brief paleoceanographic interpretation, during the MIS 5 and MIS 4 periods, was conducted by comparing mineralogical and elementary analysis aiming to reconstruct the variations of the terrigenous input to the studied area. As a conclusion, the results from XRF measurements (BTX II) presented to confirm the viability of such a technique, showing that analysis using BTX II is a reliable, cheap, rapid and non-destructive option for obtaining elementary ratios and mineralogical downcore results at high resolution, allowing stratigraphic and paleoceanographic interpretations.

Ocean and Coastal ResearchPockmarks are circular or elliptical structures formed at the seabed by the expulsion of gas from the subsurface. They are widely distributed along the continental margin off southeastern Brazil and can be over a kilometer wide and 100 meters deep. However, studies concerning the organic characteristics of these pockmark areas are scarce. This study sought to evaluate the organic composition of the sedimentary matter in pockmark areas located in the continental slope region of the southern Brazilian coast. Hydrocarbons, sterols, long-chain alcohols, stable isotopes of C and N, total organic carbon, and total nitrogen were assessed to provide an organic molecular characterization of the pockmarks located in the Southwestern Atlantic Ocean. These compounds did not reflect the organic characteristics of the scape of fluids that generate pockmark structures.

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