Greenhouse climate – insights from early and middle Eocene stratigraphic and palaeoclimatic reconstructions of the Rockall Trough, NE Atlantic

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Baranowski, Ulrike Katharina ORCID: https://orcid.org/0000-0003-3177-5936 (2020). Greenhouse climate – insights from early and middle Eocene stratigraphic and palaeoclimatic reconstructions of the Rockall Trough, NE Atlantic. University of Birmingham. Ph.D.

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Abstract

The early Eocene climate optimum (EECO) was the time of peak Cenozoic warmth with ice free poles. The EECO is an essential time interval to study climate proxies, which provide the data to test climate models under conditions of extreme greenhouse gas forcing. The relatively scarce sea surface temperature (SST) proxy data from the Eocene indicate a puzzling reduced latitudinal temperature gradient, which is difficult to reproduce in climate models. Therefore, high quality Eocene SST data with good age control are required, especially within large geographical proxy data gaps. This study presents new temperature proxy data from mixed layer (Acarinina bullbrooki, pF-SSTs) and thermocline dwelling (Subbotina eocaena, pF-STT) planktic foraminiferal oxygen isotopes and from thaumarchaeotal membrane lipids (SST-H). This data is underlain by a new age model based on high-resolution bulk carbonate oxygen and carbon isotopes and nannofossil biostratigraphy from Site 16/28-sb01, NE (North East) Atlantic (palaeolatitude 49˚N). Carbon isotope excursions (CIE) P, R, S, T, U, V and W are detected within the EECO bulk isotope record of Site 16/28-sb01. Within this CIEs, elemental variability (XRF), foraminiferal abundance, temperatures and radiolarian abundance do not show a systematic response linked to the carbon cycle perturbations. Therefore, it is concluded that the main causes for variability at this shallow Site, is likely salinity variability coupled to an enhanced hydrologic cycle, sedimentary system ageing and subsidence. Site 16/28-sb01, subsided from ~300 to ~1000 m water depth from the early Eocene to the middle Eocene. In the EECO both SST-H and pF-SST agree on an average temperature of ~28˚C confirming a greatly reduced EECO latitudinal SST gradient (and pF-STT ~19˚C). In the middle Eocene the SST proxies show a pronounced offset, with SST-H implying ~28˚C and pF-SSTs ~17˚C (pF-STT ~15˚C). This SST offset in the middle Eocene is most likely caused by a combination of slight change of d18OSW combined with either a slight winter bias of A. bullbrooki, a slightly deeper depth habitat of A. bullbrooki or a less stratified water column in the middle Eocene compared to the early Eocene. The unconformity between early and middle Eocene at Site 16/28-sb01 might be caused by a more erosional regime linked to Northern Component deep water onset around ~49 Ma.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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