Middle Eocene climate cyclicity in the southern Pacific: implications for global ice volume

Burgess, Catherine Elizabeth, Pearson, Paul Nicholas ORCID: https://orcid.org/0000-0003-4628-9818, Lear, Caroline Helen ORCID: https://orcid.org/0000-0002-7533-4430, Morgans, Hugh E. G., Handley, Luke, Pancost, Richard D. and Schouten, Stefan 2008. Middle Eocene climate cyclicity in the southern Pacific: implications for global ice volume. Geology 36 (8) , pp. 651-654. 10.1130/G24762A.1

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Abstract

We use a multiproxy approach to determine surface and bottom water temperatures off the coast of New Zealand during the middle Eocene and to constrain the δ18O of seawater. We use these data to place constraints on the size and variability of global ice sheets at that time. The Hampden Section in South Island is characterized by exceptionally well preserved micro fossils and clear sedimentary cyclicity, providing a remarkable window into conditions at paleo latitude ~55°S in the Pacific Ocean. The cyclicity was studied in detail over a ~4 m section corresponding to an interval of ~70 k.y., ca. 41.7 Ma. The sedimentary cycles are defined by fluctuations in the sand (>63 μm) component, occurring on a wavelength of ~1 m, corresponding to Milankovitch-scale frequency. Analyses of foraminifer oxygen isotopic (δ18 O) and Mg/Ca composition, combined with TEX86 analyses from organic carbon, are used to generate records of seawater temperature and oxygen isotopic composition (δ18OSW). These indicate bottom water temperatures of ~11–13 °C and sea surface temperatures of ~23–25 °C with good agreement between the proxies. Temperature cyclicity with a magnitude of ~1.5 °C occurs in both surface and bottom waters, approximately in phase with the sedimentary cycles. Estimates of δ18OSW have a mean value of −1.2‰ throughout the study section. Taken together, the data suggest a largely ice-free world with orbital-scale cycles expressed as temperature and hydrological variation with little or no ice volume change.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Chemistry Earth and Environmental Sciences
Subjects:	G Geography. Anthropology. Recreation > GC Oceanography Q Science > QE Geology
Uncontrolled Keywords:	Eocene; paleoclimate; ice; temperature; cyclicity; New Zealand
Publisher:	Geological Society of America
ISSN:	0091-7613
Last Modified:	02 Jan 2025 15:43
URI:	https://orca.cardiff.ac.uk/id/eprint/5878

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