Palaeoclimate and biotic records from the Uruguayan Margin

The Brazilian-Malvinas Confluence (BMC) dominates western South Atlantic margin oceanography, marking a distinct mixing region between the tropical Brazil Current and sub-polar Malvinas Current. Tracing this confluence requires a readily available proxy, sensitive to the contrasting BMC water masses. Planktonic foraminifera are unicellular marine plankton that construct a calcium carbonate test, these tests are abundant in the fossil record, enabling analysis of past environments. The BMC migrates along the margin over a range of timescales, with variation impacting wider regional oceanography and climate. Using planktonic foraminifera, this study assesses BMC regional spatial and temporal variation, utilising: planktonic foraminiferal assemblages, single specimen stable isotope analysis, ITRAX XRF scanning and new radiocarbon dating, reconstructing modern and past Holocene signals. These techniques targeted three aims 1) assessment of spatial variability of planktonic foraminiferal core top records in relation to the modern setting, 2) investigation of BMC evolution over the last 10 Kyr, tracking confluence movement in relation to a single site, and 3) evaluation of water mass specific morphotypes and variable test encrustation states on the isotopic signals recorded by Globoconella inflata, a key species in oceanographic studies. Use of high-density spatial mapping of assemblages and isotopic measurements reveals significant heterogeneity between sites, at a resolution normally unobtainable to similar studies. Assemblage and stable isotope variability continue downcore, alongside ITRAX productivity spikes, coinciding with ENSO intensification. Variation corresponds with mid-Holocene BMC southern migration, supporting Argentine and Brazilian studies. Investigation into increasing encrustation and increasing stable oxygen isotope values finds little correlation when using single specimens, contrasting previous work. However, this study provides recommendations for resolving morphotype/encrustation influences on δ18O records. This study emphasises the value of high-density spatial and temporal sampling in understanding complex oceanographic regions, and promotes single specimen isotopes for fingerprinting water mass signatures and deciphering BMC morphotype/encrustation δ18O signals.