A POTENTIAL OXYGEN MINIMUM ZONE FROM SOUTHWESTERN SOUTH ATLANTIC OCEAN DURING THE HEINRICH STADIAL 1

Oxygen Minimum Zones (OMZ) are water layers characterized by low oxygen saturation state in response to a complex interplay of biological, chemical, and physical processes. OMZ are typically found along the western side of continents (i.e., Arabian Sea, Easten Pacific Ocean, Eastern Tropical Atlantic Ocean, and Southeastern South Atlantic Ocean). Nevertheless, little is known about the southwestern South Atlantic (Brazil), specifically within the continental shelf of Santos Basin, which is near the Cabo Frio upwelling system. We here reconstruct the paleoenvironmental conditions from the 230-cm-thick C4-GC-2 core (25°51.519’S/ 45°30.685’W, 395 m water depth, southwestern South Atlantic Ocean). To achieve this goal, we constructed the age model based on four samples (6-8 cm, 38-40 cm, 83-85 cm, 113-115 cm), provided oxygen and carbon isotope records on the benthic foraminifera Cibicidoides sp. and analysed foraminiferal assemblages. The record encompasses the Heinrich Stadial 1 (HS1, 17.8-15.7 kyr). The enrichment in δ18O values indicate prevailing cold conditions during the H1 and/or enhanced upwelling. The relatively low values of δ13C are comparable of those Cibicidoides wuellerstorfi from East Pacific Ocean (site TR163-25) during the same time interval. The benthic foraminiferal assemblage is predominantly dominated by Bolivina spp. (~80%) and subordinately by Globobulimina spp. (~15%). The predominance of low-oxygen tolerant benthic foraminifera might suggest for the presence of oxygen deficiency potentially associated to OMZ in the Southwestern South Atlantic at a relatively shallow depth (395 m) instead of a methane cold seep. The cold conditions during the H1 likely promoted the upwelling of nutrient-rich water in the Southwestern South Atlantic, which favoured the proliferation of low-oxygen tolerant species. The poor ventilation during the H1 further prevented the oxygenation of bottom waters and thus, limiting the diversity of benthic foraminifera community.