Gateway-driven weakening of ocean gyres leads to Southern Ocean cooling

Abstract

Declining atmospheric CO2 concentrations are considered the primary driver for the Cenozoic Greenhouse-Icehouse transition, ~34 million years ago. A role for tectonically opening Southern Ocean gateways, initiating the onset of a thermally isolating Antarctic Circumpolar Current, has been disputed as ocean models have not reproduced expected heat transport to the Antarctic coast. Here we use high-resolution ocean simulations with detailed paleobathymetry to demonstrate that tectonics did play a fundamental role in reorganising Southern Ocean circulation patterns and heat transport, consistent with available proxy data. When at least one gateway (Tasmanian or Drake) is shallow (300 m), gyres transport warm waters towards Antarctica. When the second gateway subsides below 300 m, these gyres weaken and cause a dramatic cooling (average of 2–4 °C, up to 5 °C) of Antarctic surface waters whilst the ACC remains weak. Our results demonstrate that tectonic changes are crucial for Southern Ocean climate change and should be carefully considered in constraining long-term climate sensitivity to CO2.

Climate transition at the Eocene–Oligocene influenced by bathymetric changes to the Atlantic–Arctic oceanic gateways

“…The proto-ACC is considerably weaker (∼10 to 15 Sv; Fig. 4 C ) than the present-day ACC at ∼150 Sv ( 46 ), although similar in strength to other recent model studies ( 47 ). A weak ACC could partly explain the lack of influence on Antarctic surface air temperatures and is expected in this configuration as the Southern Ocean gateways were narrower and shallower that today.…”

Progressive Intensification of Pacific Deep Water Circulation Since the Early Pliocene

“…Plate tectonics is indirectly controlling the long‐term global ocean circulation at million‐year timescales, through opening/closing, or deepening/shallowing of oceanic gateways, arcs, ridges, basins, and other tectonic features (Knutz, 2008; Paxman et al., 2019; Sauermilch et al., 2021; Straume et al., 2020; Yin et al., 2021). The Pacific plate and its coupled local plates have been moving northwest since at least the late Miocene (Hall, 2002; Müller et al., 2016; Wu et al., 2016).…”

“…However, the cooling climate, especially since the Pleistocene, may induce more AABW production by brine rejection due to increased sea ice, and facilitate PDW to reach a more vigorous threshold at some particular times, proposed here at 2.15 and 0.96 Ma (Figure 3). Plate tectonics is indirectly controlling the long-term global ocean circulation at million-year timescales, through opening/closing, or deepening/shallowing of oceanic gateways, arcs, ridges, basins, and other tectonic features (Knutz, 2008;Paxman et al, 2019;Sauermilch et al, 2021;Straume et al, 2020;Yin et al, 2021). The Pacific plate and its coupled local plates have been moving northwest since at least the late Miocene (Hall, 2002;Müller et al, 2016;Wu et al, 2016).…”

A revised phylogenetic classification forViola(Violaceae)

“…Plagiostigma and sect. Viola (Figures 12,32) was generated based on concatenated sequences of the eight nuclear regions GPI-C (CHAM homoeolog), GPI-M (MELVIO homoeolog), NRPD2a-C (CHAM homoeolog), NRPD2a-M (MELVIO homoeolog), ITS-C (CHAM homoeolog), ITS-M (MELVIO homoeolog), SDH-C (CHAM homoeolog), and SDH-M (MELVIO homoeolog) (Table 7). The analysis was set up in BEAUTi v1.…”

“…Viola, like Violaceae as a whole, is assumed to have originated in South America [2,4,28,29]. Dating analysis associates the origin and beginning diversification of Viola with the Eocene-Oligocene cooling event [30][31][32] which, in combination with the formation of the Andes during the Eocene [33][34][35][36], may have given this temperate lineage opportunities to diversify [4,28].…”