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.