Sea surface temperature evolution of the North Atlantic Ocean across the Eocene–Oligocene transition

Climate of the past

article

Kasia K. Śliwińska¹  Helen K. Coxall³  David K. Hutchinson³  Diederik Liebrand⁶  Stefan Schouten²  Agatha M. de Boer³ 

[1]Department of Geoenergy and Storage

[2]Department of Marine Microbiology and Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research

[3]Department of Geological Sciences, Stockholm University

[4]Bolin Centre for Climate Research, Stockholm University

[5]Climate Change Research Centre, University of New South Wales

[6]National Oceanography Centre

[7]Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Vening Meinesz building A, Princetonlaan 8a

DOI  :  10.5194/cp-19-123-2023

学科分类：社会科学、人文和艺术（综合）

来源: Copernicus Publications

【 摘 要 】

A major step in the long-term Cenozoic evolution toward aglacially driven climate occurred at the Eocene–Oligocene transition (EOT), ∼34.44 to 33.65 million years ago (Ma). Evidence for high-latitude cooling and increased latitudinal temperature gradients across theEOT has been found in a range of marine and terrestrial environments.However, the timing and magnitude of temperature change in the NorthAtlantic remains highly unconstrained. Here, we use two independent organicgeochemical palaeothermometers to reconstruct sea surface temperatures(SSTs) from the southern Labrador Sea (Ocean Drilling Program – ODP Site647) across the EOT. The new SST records, now the most detailed for theNorth Atlantic through the 1 Myr leading up to the EOT onset,reveal a distinctive cooling step of ∼3   ∘ C (from27 to 24  ∘ C), between 34.9 and 34.3 Ma, which is ∼500  kyr prior to Antarctic glaciation. This cooling step,when compared visually to other SST records, is asynchronous across Atlanticsites, signifying considerable spatiotemporal variability in regional SSTevolution. However, overall, it fits within a phase of general SST coolingrecorded across sites in the North Atlantic in the 5 Myrbracketing the EOT. Such cooling might be unexpected in light of proxy and modelling studiessuggesting the start-up of the Atlantic Meridional Overturning Circulation(AMOC) before the EOT, which should warm the North Atlantic. Results of anEOT modelling study (GFDL CM2.1) help reconcile this, finding that areduction in atmospheric CO 2 from 800 to 400 ppm may be enough tocounter the warming from an AMOC start-up, here simulated throughArctic–Atlantic gateway closure. While the model simulations applied hereare not yet in full equilibrium, and the experiments are idealised, theresults, together with the proxy data, highlight the heterogeneity ofbasin-scale surface ocean responses to the EOT thermohaline changes, withsharp temperature contrasts expected across the northern North Atlantic aspositions of the subtropical and subpolar gyre systems shift. Suggestedfuture work includes increasing spatial coverage and resolution of regionalSST proxy records across the North Atlantic to identify likely thermohalinefingerprints of the EOT AMOC start-up, as well as critical analysis of thecauses of inter-model responses to help better understand the drivingmechanisms.

【 授权许可】

CC BY