Absence of a strong, deep-reaching Antarctic Circumpolar Current zonal flow across the Tasmanian gateway during the Oligocene to early Miocene

• Published in: Global and Planetary Change
• Main Authors: Evangelinos, Dimitris, Escutia, Carlota, van de Flierdt, Tina, Valero, Luis, Flores, José-Abel, Harwood, David M., Hoem, Frida S., Bijl, Peter, Etourneau, Johan, Kreissig, Katharina, Nilsson-Kerr, Katrina, Holder, Liam, López-Quirós, Adrián, Salabarnada, Ariadna
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2022
• Subjects: Antarctic; Emerald Basin; Pacific; Ross Sea; The Antarctic; Antarc*; Ice Sheet
• Online Access: https://oro.open.ac.uk/81298/; https://doi.org/10.1016/j.gloplacha.2021.103718

The vigorous eastward flow of the Antarctic Circumpolar Current (ACC) connects all major ocean basins and plays a prominent role in the transport of heat, carbon and nutrients around the globe. However, the establishment of a deep circumpolar flow, similar to the present-day ACC, remains controversial thereby obscuring our understanding of its climatic impact. Deciphering the chemical composition of Circumpolar Deep Water (CDW) within the ACC can provide critical insights about its development and evolution. Here we present new fossil fish teeth/bone debris neodymium isotope (ε Nd ) records from Deep Sea Drilling Project (DSDP) Sites 278 and 274 in the southwest Pacific Ocean, with the aim to trace changes in deep water masses across the Tasmanian Gateway between the early Oligocene and early Miocene (~ 33–22 Ma). Site 274 provides the first Nd isotope record proximal to the Ross Sea during the Oligocene (33.5–23.4 Ma). Its Nd isotope composition shows excursions to very radiogenic values, ε Nd(t) = −3.1 and ε Nd(t) = − 3.7, at 33.5 Ma and 23.8 Ma, respectively, in response to major steps in Antarctic ice sheet expansion. A shift to lower, more unradiogenic ε Nd(t) values between 29.7 and 29.1 Ma is linked to an increased influence of proto-CDW upwelling at the site. In contrast, the Nd isotope record from Site 278 in the southern Emerald Basin shows little variability (ε Nd(t) = −6.0 to −6.7) throughout the Oligocene and early Miocene (30.9–21.8 Ma). Comparison with published data north of the ACC path, demonstrates the presence of two deep water masses in the South Pacific prior to the inferred onset of the ACC (33–30 Ma), one occupying depths between ~2500 and 3000 m (ε Nd(t) = ~ −3 to −5) and a deep/bottom water mass (> 3000 m) with a more unradiogenic Nd isotope composition (ε Nd(t) = ~ −6). Site 278 located close to the proto-polar front (proto-PF) indicates that following the inferred onset of the ACC, deep waters bathing the southern Emerald Basin remained more radiogenic in the Southwest Pacific ...