Infaunal and epifaunal benthic foraminifera species as proxies of organic matter paleofluxes in the Pelotas Basin, south-western Atlantic Ocean

One late Quaternary sediment core from the continental slope of the northern sector of Pelotas Basin (southern Brazilian continental margin, 2091 m water depth) was analyzed in order to evaluate the influence of the organic matter influx in the benthic foraminiferal assemblage composition on a regional scale. This study investigated the relationship between epifaunal species (Epistominella exigua and Alabaminella weddellensis) and infaunal species (Uvigerina peregrina and Angulogerina angulosa) integrated in a relative abundance based index, the “Organic Input Index” (OrgIn). The correlation of these species with abiotic data is also discussed, including mud content, total organic carbon (TOC) and carbon stable isotope (δ13C) in Uvigerina peregrina. The age model based on one radiocarbon dating of planktonic foraminifera and oxygen isotope composition of benthic foraminifera (Uvigerina) revealed the record spans the last 112,500 yr, covering the Marine Isotope Stages (MIS) 5 to 3. The dominance of infaunal species, mainly Globocassidulina subglobosa, boliviniids and buliminiids throughout the entire core is interpreted as an indicator of an increase of organic matter supply and dominance of the eutrophic conditions in this study area. The variations found in the proportion of the epifaunal and infaunal species indicate distinctive inputs of organic matter (phytodetritus input versus bacterial activity, respectively). An increasing trend in the importance of epifaunal species from the base of the core to uppermost samples (MIS 5 to MIS 3) was also observed, which is assumed to be evidence of the higher productivity of the surface water masses in this sector of the South Atlantic during the glacial periods.