Benthic foraminiferal distributions on the Uruguayan continental margin (South-western Atlantic) and controlling environmental factors

The data on benthic foraminifera analysed from 110 box-core samples collected on the Uruguayan continental margin (outer shelf and upper and middle slope, between 36.54–34.64°S and 51.66–53.71°W) were used to evaluate the distribution of the benthic foraminiferal fauna and its relationship with selected abiotic parameters. Primary productivity (PP) and the organic flux (Jz) reaching the sea floor were also estimated for comparison with the foraminiferal distributions. The study area was characterised by elevated PP and Jz values, mainly in the southernmost region, which were associated with thermohaline fronts due to the presence of the Subtropical Shelf Front. The dominant identified taxa were Rhumblerella sepetibaensis (this is the first study recording the ecology of this species) and the opportunistic species Epistominella exigua, Bulimina spp. and Reophax fusiformis, which displayed maximal densities at the southernmost stations, concurrent with the highest Jz levels. The dominant species and vertical foraminiferal distributions responded to the different environmental conditions impacting the area (e.g. PP, grain size, nutrient content), which were most likely related to the hydrodynamic conditions. Hydrodynamic conditions cause differences in PP according to the locations of water masses and their fronts at the surface, according to the depth and current intensity; they determined energetic differences across the benthic environment, controlling organic matter sedimentation as well as grain size, which influenced oxygen availability within sediments.