Drake Passage gateway opening and Antarctic Circumpolar Current onset 31 Ma ago: The message of foraminifera and reconsideration of the Neodymium isotope record

Abstract

The establishment of the Antarctic Circumpolar Current (ACC) is one of the most important events for both global oceanic circulation and climate of the Cenozoic. The onset of this major current hinges on the opening of two major oceanic passages, the Drake Passage and the Tasmanian gateways that connect Pacific, Atlantic and Indian oceans allowing a modern-like thermohaline circulation. For decades, the ACC onset has been considered as the trigger of the Oligocene glaciation at 33.7 Ma, which marks the beginning of the modern icehouse climate. Today, this scenario is debated. The main obstacle to evaluate the ACC influence on the Oligocene glaciation remains the ill-constrained timing of the Drake Passage gateway opening. Here, we analyse the geochemical composition and Sr isotope ratio of dated planktonic and benthic foraminifera from two IODP and ODP legs in the Southern Atlantic and Pacific oceans (SAO and PO, respectively) to assess the variability of seawater masses' chemical composition through time and to better constrain the timing of the Drake Passage gateway opening along the Eocene-Oligocene interval. These results, based on seawater paleo temperature (Mg/Ca molar ratios), redox (Ce/Ce* anomaly) and provenance ( 87 Sr/ 86 Sr) proxies, highlight a gradual seawater mass mixing between the SAO and PO from 31 Ma to 26 Ma. Combined with a reconsideration of the fossil fish teeth Neodymium isotope records, these geochemical tracers evidencing the SAO-PO interconnection depicts the Drake Passage gateway opening and deepening during this 31-26 Ma interval and thus, the timing of the ACC onset. Hence, antecedence of the Oligocene glaciation onset (at 33.7 Ma) relative to the ACC onset (31-26 Ma) implies that the ACC did not trigger the Oligocene glaciation and that the role of atmospheric pCO2 should be further considered.

Eocene palaeoenvironments and palaeoceanography of areas adjacent to the Drake Passage: insights from dinoflagellate cyst analysis

“…Alternatively, the deepening of such passage allowing the onset of the ACC, was dated by Hodel et al . (2021) to the earliest Oligocene (31 Ma), a late date that thus favours the pCO 2 hypothesis.…”

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

“…We only selected entire, clean and well-preserved specimens devoid of visible recrystallization, clay aggregates and oxyhydroxide patches (Figure 3). Each planktic and benthic foraminifera sample was then cleaned and digested in a clean laboratory following the procedure of Hodel et al (2021). Foraminifera tests cleaning method consists of several ultrasonications in MQ water (Molina-Kescher et al, 2014;Osborne et al, 2017;Hodel et al, 2021) rather than the oxidizing-reducing cleaning of Barker et al (2003).…”

“…Antarctica and the surrounding Southern Ocean have been a significant focus of the last decades given their high sensitivity to cooling and glaciation during the Eocene-Oligocene (e.g., Kennett et al, 1975;Nelson and Cooke, 2001;Zachos et al, 2001;Stickley et al, 2004;Bijl et al, 2009;Bohaty et al, 2012;Hollis et al, 2012Hollis et al, , 2015Scher et al, 2014Scher et al, , 2015Pascher et al, 2015;Hodel et al, 2021;Sauermilch et al, 2021;Shepherd et al, 2021). Located at the outlet of the Tasmanian gateway, the DSDP Site 277 on the Campbell Plateau (Figure 1) was drilled specifically to investigate the role played by the Antarctic Circumpolar Current (ACC) in the thermal isolation of Antarctica from tropical heat fluxes (e.g., Kennett et al, 1975) (Figure 1).…”

“…We applied several chemical proxies to planktic and benthic foraminifera from Site 277: (1) Mg/Ca and δ 18 O ratios to infer seawater temperature and ice-volume evolution, (2) Ce anomaly (Ce/Ce*) as a seawater redox proxy, (3) U/Ca ratio as a sedimentary redox proxy, and (4) the δ 13 C as a potential paleoproductivity proxy in combination with sedimentation rates (e.g., Katz et al, 2010 for a review, Chase et al, 2001;Boiteau et al, 2012;Chen et al, 2017;Remmelzwaal et al, 2019;Hodel et al, 2021). All these proxies were analyzed for both benthic (mixed Gyroidinoides sp.…”

The Nazca Drift System – palaeoceanographic significance of a giant sleeping on the SE Pacific Ocean floor

“…6), implying a maximum age of c. 36.8 Ma at the base (sedimentation rate of 2.55 m Ma −1 ; King & Wade, 2017), which is younger than the initiation of the opening of the Drake Passage (41 Ma; Scher & Martin, 2006). The initiation of the Nazca Drift System could be related to the opening of the Drake Passage and the northward branch bifurcation of the ACC along the Pacific margin of South America (Lawver & Gahagan, 1998;Hodel et al 2021).…”