Abstract
A major step in the long-term Cenozoic evolution toward a glacially driven climate occurred at the Eocene-Oligocene transition (EOT), ∼1/434.44 to 33.65 million years ago (Ma). Evidence for high-latitude cooling and increased latitudinal temperature gradients across the EOT has been found in a range of marine and terrestrial environments. However, the timing and magnitude of temperature change in the North Atlantic remains highly unconstrained. Here, we use two independent organic geochemical palaeothermometers to reconstruct sea surface temperatures (SSTs) from the southern Labrador Sea (Ocean Drilling Program - ODP Site 647) across the EOT. The new SST records, now the most detailed for the North Atlantic through the 1Myr leading up to the EOT onset, reveal a distinctive cooling step of ∼1/43°C (from 27 to 24°C), between 34.9 and 34.3Ma, which is ∼1/4500kyr prior to Antarctic glaciation. This cooling step, when compared visually to other SST records, is asynchronous across Atlantic sites, signifying considerable spatiotemporal variability in regional SST evolution. However, overall, it fits within a phase of general SST cooling recorded across sites in the North Atlantic in the 5Myr bracketing the EOT. Such cooling might be unexpected in light of proxy and modelling studies suggesting the start-up of the Atlantic Meridional Overturning Circulation (AMOC) before the EOT, which should warm the North Atlantic. Results of an EOT modelling study (GFDL CM2.1) help reconcile this, finding that a reduction in atmospheric CO2 from 800 to 400ppm may be enough to counter the warming from an AMOC start-up, here simulated through Arctic-Atlantic gateway closure. While the model simulations applied here are not yet in full equilibrium, and the experiments are idealised, the results, together with the proxy data, highlight the heterogeneity of basin-scale surface ocean responses to the EOT thermohaline changes, with sharp temperature contrasts expected across the northern North Atlantic as positions of the subtropical and subpolar gyre systems shift. Suggested future work includes increasing spatial coverage and resolution of regional SST proxy records across the North Atlantic to identify likely thermohaline fingerprints of the EOT AMOC start-up, as well as critical analysis of the causes of inter-model responses to help better understand the driving mechanisms.
Original language | English |
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Pages (from-to) | 123-140 |
Number of pages | 18 |
Journal | Climate of the Past |
Volume | 19 |
Issue number | 1 |
DOIs | |
Publication status | Published - 13 Jan 2023 |
Bibliographical note
Publisher Copyright:© 2023 Kasia K. Sliwinska et al.
Funding
This research was funded by a Danish Council for Independent Research/Natural Sciences (DFF/FNU) grant (grant 11-107497) to Kasia K. Śliwińska; Swedish Research Council (VR) grants awarded to Agatha M. de Boer (2016-03912 and 2020-04791) and Helen K. Coxall (2008-2859); a Formas grant (2018-01621) and an Australian Research Council grant (DE220100279) to David K. Hutchinson; and a Netherlands Earth System Science Centre (NESSC) grant funded by the Ministry of Education, Culture and Science (OCW) to Stefan Schouten. The model simulations were enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Centre (NSC), partially funded by the Swedish Research Council through grant agreement no. 2018-05973. We thank Walter Hale at Bremen Core Repository (BCR) for collecting samples. We appreciate inspiring discussions with John Firth and Jan Backman and laboratory assistance from Anchelique Metz. This research used samples provided by the Ocean Drilling Project (ODP). ODP was sponsored by the US National Science Foundation and participating countries under the management of Joint Oceanographic Institutions. We would like to acknowledge the editor Bjørg Risebrobakken and all reviewers for their time and valuable comments, which helped to improve this paper. This research has been supported by the Natur og Univers, Det Frie Forskningsråd (grant no. 11-107497); the Svenska Vetenskapsrådet (grant nos. 2016-03912, 2020-04791, 2018-05973, and 2008-2859); the Svenska Forskningsrådet Formas (grant no. 2018-01621); the Australian Research Council grant (DE220100279); the Netherlands Earth System Science Centre (grant no. 024.002.001); and the Ministerie van Onderwijs, Cultuur en Wetenschap (grant no. 024.002.001).The article processing charges for this open-access publication were covered by Stockholm University. This research has been supported by the Natur og Univers, Det Frie Forskningsrd (grant no. 11-107497); the Svenska Vetenskapsrdet (grant nos. 2016-03912, 2020-04791, 2018-05973, and 2008-2859); the Svenska Forskningsrdet Formas (grant no. 2018-01621); the Australian Research Council grant (DE220100279); the Netherlands Earth System Science Centre (grant no. 024.002.001); and the Ministerie van Onderwijs, Cultuur en Wetenschap (grant no. 024.002.001).
Funders | Funder number |
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Cultuur en Wetenschap | |
Ministerie van Onderwijs | |
Svenska Vetenskapsrdet | |
Svenska Vetenskapsrådet | 2018-05973, 2008-2859 |
National Science Foundation | |
Natur og Univers, Det Frie Forskningsråd | 11-107497 |
Australian Research Council | DE220100279 |
Svenska Forskningsrådet Formas | 2018-01621 |
Ministerie van onderwijs, cultuur en wetenschap | |
Vetenskapsrådet | 2016-03912, 2020-04791 |
Netherlands Earth System Science Centre | 024.002.001 |
Danmarks Frie Forskningsfond |