Late Cenozoic Sea Surface Temperature evolution of the South Atlantic Ocean

• Main Authors: Hoem, Frida S., López-Quirós, Adrián, Lagemaat, Suzanna, Etourneau, Johan, Sicre, Marie-Alexandrine, Escutia, Carlota, Brinkhuis, Henk, Peterse, Francien, Sangiorgi, Francesca, Bijl, Peter K.
• Format: Text
• Language: English
• Published: 2023
• Subjects: Antarctic; Southern Ocean; The Antarctic; Drake Passage; Antarc*; Ice Sheet; South Atlantic Ocean
• Online Access: https://doi.org/10.5194/egusphere-2023-291; https://egusphere.copernicus.org/preprints/2023/egusphere-2023-291/

At present, a strong latitudinal sea-surface-temperature (SST) gradient of ∼ 16 ∘ C exists across the Southern Ocean, maintained by the Antarctic Circumpolar Current (ACC) and a set of complex frontal systems. Together with the Antarctic ice masses, this system has formed one of the most important global climate regulators. The timing of the onset of the ACC system, its development towards modern-day strength and the consequences for the latitudinal SST gradient around the southern Atlantic Ocean are still uncertain. Here we present new TEX 86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms)-derived SST records from two sites located east of Drake Passage (south-western South Atlantic) to assist in better understanding two critical time intervals of prominent climate transitions during the Cenozoic: the late Eocene–early Oligocene (Ocean Drilling Program, ODP, Site 696) and Middle–Late Miocene (IODP Site U1536) transitions. Our results show temperate conditions (20–11 ∘ C) during the first time interval, with a weaker latitudinal SST gradient ( ∼ 8 ∘ C) across the Atlantic sector of the Southern Ocean compared to present day. We ascribe the similarity in SSTs between Sites 696 and 511 in the late Eocene–early Oligocene South Atlantic to a persistent, strong subpolar gyre circulation connecting the sites, which can only exist in the absence of a strong throughflow across the Drake Passage. Surprisingly, the southern South Atlantic record Site 696 shows comparable SSTs ( ∼ 12–14 ∘ C) during both the earliest Oligocene oxygen isotope step (EOIS, ∼ 33.65 Ma) and the Miocene Climatic Optimum (MCO, ∼ 16.5 Ma). Apparently, maximum Oligocene Antarctic ice volume could coexist with warm ice-proximal surface ocean conditions, while at similar ocean temperatures, the Middle Miocene Antarctic ice sheet was likely reduced. Only a few Middle–Late Miocene (discontinuous) high-latitude records exist due to ice advances causing unconformities. Our low-resolution Site U1536 record of southern South Atlantic SSTs ...