Mid-Late Pleistocene benthic foraminifera from Southwestern South Atlantic: driven by primary productivity or water mass properties?

In the Atlantic sector of the Southern Ocean up to 35°S, Neogene benthic foraminiferal faunal changes have been inter- preted, alternatively, as changes in deep water-masses distribution and organic matter availability. In surface, the Southwestern South At- lantic presents a highly dynamic frontal zone and exhibits large spatial and temporal variability in primary productivity that influences the export of organic carbon from the euphotic zone. However, below ~1000 meters depth, it is characterized by the interaction of several water masses. For this reason, the western sector of the South Atlantic is a natural laboratory to test the benthic foraminifera's response to changes in both, the deep water-masses distribution and the exported productivity. In order to define which was the main factor control- ling the benthic foraminiferal assemblages structure during a glacial Mid-Late Pleistocene event, abundance analysis of organic matter content, oxygen availability and water masses marker species, and Q-mode factor analysis were carried out on core SP1251 (3400m; ~38°S - 54°W). Our results indicate that the benthic foraminiferal assemblages are mainly composed of high organic matter and oxygen availability-associated species revealing that productivity has been the main factor in determining the structure of the assemblages'com- position. These results also reflect that surface productivity regime would have not been uniform as a result of variations in the shelfbreak upwelling of Patagonia as a consequence of variations in the Antarctic upwelling.