The Late Miocene-Early Pliocene biogenic bloom in oligotrophic waters of the South Atlantic Subtropical Gyre

The end of the Miocene and the beginning of the Pliocene were marked by significant environmental changes, among which a paleoceanographic phenomenon known as the Late Miocene-Early Pliocene “biogenic bloom” (BB) stands out. The BB was characterized by increased accumulation of biogenic components in marine sediments, and has been recorded in regions of all modern ocean basins, although primarily in high-productivity upwelling areas. Here, we present records serving as proxies for past primary productivity and paleoclimate at Deep Sea Drilling Project (DSDP) Site 516, lying on the southern edge of the South Atlantic Subtropical Gyre (SASG). Site 516 provides a valuable record of the BB, as oceanic gyres are large, oligotrophic regions, and important sinks for atmospheric CO 2 . Our goal is to determine the onset timing and features of the BB in the SASG, as well as to explore factors that influenced regional changes in paleoproductivity. We analyzed sedimentary elemental composition, benthic and planktic foraminiferal stable carbon (δ 13 C) and oxygen (δ 18 O) isotopes, along with a faunal assessment of benthic foraminifera at Site 516. Our findings indicate that increased surface productivity began at approximately 7.8 Ma in the western SASG, roughly coinciding with the Late Miocene Carbon Isotopic Shift (LMCIS), which lasted for about 0.8 Ma. The Site 516 log(Zr/Rb) record suggests increased aeolian dust input synchronous with onset (at 7.8 Ma) and during the BB (from 7.8 to 4.3 Ma). We suggest that aridification over South America (most likely) and/or Africa contributed to the supply of aeolian dust to the SASG, driven by the strengthening of the Hadley and Walker cells, which in turn stimulated regional primary productivity. • Record of the Late Miocene Biogenic Boom (LMBB) in an oligotrophic subtropical gyre. • LMBB onset coeval to the Late Miocene Carbon Isotopic Shift (LMCIS). • Aridification over South America supplied aeolian dust, sustaining high productivity.