Eocene-Oligocene southwest Pacific Ocean paleoceanography new insights from foraminifera chemistry (DSDP site 277, Campbell Plateau)

Abstract

Despite its major role in the Earth’s climate regulation, the evolution of high-latitude ocean dynamics through geological time remains unclear. Around Antarctica, changes in the Southern Ocean (SO) circulation are inferred to be responsible for cooling from the late Eocene and glaciation in the early Oligocene. Here, we present a geochemical study of foraminifera from DSDP Site 277 (Campbell Plateau), to better constrain thermal and redox evolution of the high latitude southwest Pacific Ocean during this time interval. From 56 to 48 Ma, Mg/Ca- and δ18O-paleothermometers indicate high surface and bottom water temperatures (24–26°C and 12–14°C, respectively), while weak negative Ce anomalies indicate poorly oxygenated bottom waters. This is followed by a cooling of ∼4° between 48 and 42 Ma, possibly resulting from a weakening of a proto-EAC (East Australian Current) and concomitant strengthening of a proto-Ross gyre. This paleoceanographic change is associated with better ventilation at Site 277, recorded by an increasing negative Ce anomaly. Once this proto-Ross gyre was fully active, increasing biogenic sedimentation rates and decreasing Subbotina sp. δ13C values indicate enhanced productivity. This resulted in a shoaling of the oxygen penetration in the sediment pile recorded by increasing the foraminiferal U/Ca ratio. The negative Ce anomaly sharply increased two times at ∼35 and ∼31 Ma, indicating enhanced seawater ventilation synchronously with the opening of the Tasmanian and Drake Passage gateways, respectively. The Oligocene glaciation is recorded by a major increase of bottom seawater δ18O during the EOT (Eocene-Oligocene Transition) while Mg/Ca-temperatures remain rather constant. This indicates a significant ice control on the δ18O record.

Calcareous Nannofossils and Paleoclimatic Evolution Across the Eocene‐Oligocene Transition at IODP Site U1509, Tasman Sea, Southwest Pacific Ocean

“…Arrows represents cooler (blue) and warmer (red) oceanic currents, as synthetized by Hodel et al. (2022) and compared with recent findings from Sauermilch et al. (2021) and Nooteboom et al.…”

“…Viganò et al, 2024a). Arrows represents cooler (blue) and warmer (red) oceanic currents, as synthetized by Hodel et al (2022) and compared with recent findings from Sauermilch et al (2021) and Nooteboom et al (2022). The approximate position of the pSTF is inferred from Nelson and Cooke (2001).…”

“…Approximately at the same time a major reconfiguration of basin and ridge topography occurred within the Tasman Sea area, with the permanent subsidence (>2,000 m) of the NCT caused by subduction initiation of the Australia-Pacific convergent plate boundary (Sutherland et al, 2010). At higher latitudes, as the buildup of ice sheets on east Antarctica began (e.g., Zachos et al, 1994) and the opening of the TG occurred, cool surface waters developed south of the proto-STF (pSTF) as part of a developing early ACC (Hodel et al, 2022;Nelson & Cooke, 2001;Sauermilch et al, 2021), possibly reaching both southern Australia and New Zealand (Kamp et al, 1990). In the latest Eocene, there is evidence of a gyre known as the proto-Ross Gyre (pRG) in the Pacific sector of the Southern Ocean (Exon, Kennett, Malone et al, 2000; Paleoceanography and Paleoclimatology 10.…”

“…Two groups of hypotheses exist to explain the onset and development of Antarctic ice sheets: (a) “the ocean‐gateway hypothesis” and (b) “the CO 2 hypothesis”. The “ocean‐gateway hypothesis”, first proposed in the late 1970's, suggests that the opening of Southern Ocean gateways (Exon, Kennet, Malone et al., 2001; Hodel et al., 2022; Livermore et al., 2007; Scher et al., 2015) allowed for a rapid intensification of the Antarctic Circumpolar Current (ACC), which reduced poleward heat flux and thermally isolated Antarctica (Kennett, 1977; Sijp et al., 2004). Subsequent modeling and proxy studies suggest that a global decline in atmospheric CO 2 drove global cooling and ice sheet growth at the EOT (Anagnostou et al., 2016; DeConto & Pollard, 2003; Pagani et al., 2011; Pearson et al., 2009; Zachos & Kump, 2005), with ice‐sheet feedbacks and changes in paleoceanography playing a secondary role (Hutchinson et al., 2021; Sauermilch et al., 2021).…”

Atmospheric CO2 Estimates for the Late Oligocene and Early Miocene Using Multi‐Species Cross‐Calibrations of Boron Isotopes

“…Two relatively understudied yet climatically relevant intervals of Earth history are the Oligocene epoch (33–23 million years ago, Ma) and early Miocene (23–16 Ma). Terrestrial, sea surface, and ocean thermocline temperatures at that time are thought to have been higher than today, with greatly‐reduced latitudinal temperature gradients that are difficult to reproduce with climate models and are not easily reconcilable with the relatively few CO 2 estimates that have been generated for this period (Burls et al., 2021; Hodel et al., 2022; O’Brien et al., 2020). Deep ocean temperatures were substantially warmer than the modern, ranging between ∼6 and 10°C from the early Oligocene through the early Miocene (Figure 1b).…”