In:
Climate of the Past, Copernicus GmbH, Vol. 19, No. 1 ( 2023-01-13), p. 123-140
Abstract:
Abstract. A major step in the long-term Cenozoic evolution toward a
glacially 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 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 1 Myr leading up to the EOT onset,
reveal a distinctive cooling step of ∼3 ∘C (from
27 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 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 5 Myr
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 400 ppm 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.
Type of Medium:
Online Resource
ISSN:
1814-9332
DOI:
10.5194/cp-19-123-2023
DOI:
10.5194/cp-19-123-2023-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2023
detail.hit.zdb_id:
2217985-9
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