Description: Depositional and paleoenvironmental studies using organic geochemical proxies often present the temporal evolution of several compounds. Despite the importance of using several proxies to understand how the surrounding environment changed through time, this large amount of data usually hampers interpretations. In this scenario, the use of statistical tools for time series analysis can help simplify and interpret large data sets, even if they were not initially developed for molecular marker data. In this study, we show the benefits of using two different cluster analyses in order to: (i) group compounds with similar sources; and (ii) identify temporal zones. Cluster analysis using SAX (Symbolic Aggregate approXimation) representation groups together different proxies with similar sources (whether anthropogenic or natural, autochthonous or allochthonous), based on their temporal evolution. Temporal zones, on the other hand, can be identified by using a constrained cluster analysis, in which samples (sediment layers) are grouped according to the temporal variability of the organic compounds. These two approaches were successfully applied to organic proxy datasets from two sediment cores, retrieved from distinct environments and with distinct temporal recoveries. Based on these analyses, we were able to identify the probable source of compounds with multiple sources, and to show how the terrestrial and marine organic matter presented distinct patterns over time. These techniques do not replace the study of the temporal evolution of compounds individually but synthesize a large amount of information and may indicate which compounds of an assemblage yield the most robust information in environmental studies.

Description: Millennial-scale oscillations are known to be important in the climatic evolution of the Atlantic basin, but which internal processes originates these oscillations are still uncertain. In this study, we investigated how the Greenland and Antarctic climates affect the SW Atlantic through basin-wide oceanographic features (such as the NADW formation and the Agulhas leakage). We reconstructed sea surface and subsurface temperatures (SST and subT) using three lipid-based biomarker proxies (UK’37, TEX86 and LDI indexes) from a sediment core (NAP 63-1) retrieved from the SW Atlantic slope (24.8°S, 44.3°W). This location allowed us to evaluate the temperature oscillations of the Brazil Current without any terrigenous or upwelling-derived biases. Both TEX86-based and LDI-based estimates represent the mean annual SST, while the UK’37-based estimates represent the subT (around 30m water depth). The periods with the most well-mixed water column were observed during intervals of cooling orbital trends due to the time required to transfer the surface cooling to the subsurface. The temperature reconstructions showed a general colder MIS 3 when compared to the MIS 4. They also showed evidence of a late response to deglaciation, with its onset in the SW Atlantic occurring in the middle of the Last Glacial Maximum. Based on these reconstructions, the NAP 63-1 SST orbital-scale trend seems to be linked to the Antarctic climate, influenced by local insolation changes. These temperature records also presented a clear millennial periodicity around 8 kyr. On this timescale, the millennial oscillations in the SW Atlantic's SST are likely linked to the NADW formation