Planktonic foraminifera, calcareous nannoplankton and ascidian variations during the last 25 kyr in the Southwestern Atlantic: A paleoproductivity signature?

Micropaleontological and geochemical analyses from western South Atlantic core SAN-76 (off Southeast Brazil) revealed changes in stable isotope values, and in the assemblages of calcareous nannoplankton and planktonic foraminifera during the past 25 kyr that point to significant paleoceanographic and climatic changes leading to an increase in productivity during the last deglaciation. The enhanced surface productivity was clearly indicated by increased relative abundances of the planktonic foraminifera Globigerina bulloides and Neogloboquadrina dutertrei and the decreased values of δ13C in planktonic foraminiferal tests. A coeval shoaling of the nutricline and thermocline was indicated by decreased relative abundances of the calcareous nannoplankton Florisphaera profunda and an increased relative abundance of the planktonic foraminifera Globorotalia truncatulinoides (right coiling). We speculate that these changes are related to N-S shifts of the Atlantic Intertropical Convergence Zone (ITCZ). A significant increase in the Cd/Ca ratio and decrease in δ13C values in the benthic foraminifer Hoeglundina elegans, along with a significant increase in the relative abundance of ascidian spicules during the deglaciation suggest that benthic communities in this area strongly benefited from increased surface water productivity.