Planktonic foraminifera assemblages from the Brazil-Malvinas Confluence: palaeoceanographic implications of sub-surface temperature reconstructions in the western South Atlantic

Planktonic foraminifera census data have been widely used to reconstruct changes in ocean ecosystems as well as ocean chemistry and circulation through calibration functions. Here we analyse new core-top census data from 22 sites in the western South Atlantic, improving the geographical coverage and spatial resolution of the environmental gradients from the region covered by the Brazil-Malvinas Confluence (similar to 38 degrees S-53 degrees W). We combine them with previous data to provide an up-to-date compilation of the western South Atlantic planktonic foraminifera-calibration data set. We study the relationship between the assemblages present in the core-top samples and the most dynamic environmental variables from the region to establish the environmental variable(s) more resolved by the assemblages. Therefore, we develop and assess a new calibration function using the data set and testing several statistical models at different water depths. Our results reveal that the distribution and abundance of the species in the Brazil-Malvinas Confluence region mainly reflect the influence of two environmental variables: the mixed layer temperature and mixed layer depth (57% of total variance). The most precise reconstructions were obtained when using sub-surface temperatures between 40 and 50 m water depth. The application of the calibration function to a Holocene sediment core at similar to 37 degrees S-53 degrees W revealed mean annual sub-surface temperature reconstructions between 8 degrees C and 11 degrees C, confirming the northward displacement of the Brazil-Malvinas Confluence during the onset of the Holocene and suggesting a major influence of the Malvinas Current during the entire Holocene at the studied site.

Automated summary

The study analyzed planktonic foraminifera data from the Brazil-Malvinas Confluence region, finding that species distribution and abundance are mainly influenced by mixed layer temperature and depth, with the most accurate reconstructions using sub-surface temperatures. Applying a new calibration function to a sediment core from the Holocene revealed a northward displacement of the Brazil-Malvinas Confluence and a significant influence of the Malvinas Current throughout the entire Holocene.