No abstract

Sea-surface temperature (SST) estimates of ~30 °C from planktic foraminifera and archaeal membrane lipids in bathyal sediments in the Canterbury Basin, New Zealand, support paleontological evidence for a warm subtropical to tropical climate in the early Eocene high-latitude (55°S) southwest Pacifi c. Such warm SSTs call into question previous estimates based on oxygen isotopes and present a major challenge to climate modelers. Even under hypergreenhouse conditions (2240 ppm CO 2 ), modeled summer SSTs for the New Zealand region do not exceed 20 °C. on June 6, 2015 geology.gsapubs.org Downloaded from

[1] We reconstruct eustatic variations during the latest Paleocene and earliest Eocene ($58-52 Ma). Dinoflagellate cysts, grain size fractions, and organic biomarkers in marine sections at four sites from three continents indicate an increased distance to the coast during the Paleocene-Eocene thermal maximum (PETM). The same trend is recognized in published records from other sites around the world. Together, the data indicate a eustatic rise during the PETM, beginning 20 to 200 ka before the globally recorded negative carbon isotope excursion (CIE) at $55.5 Ma. Although correlations are tentative, we recognize other global transgressions during Chrons C25n and C24n. The latter may be associated with Eocene Thermal Maximum 2 ($53.5 Ma) or the ''X''-event ($52 Ma). These results suggest a link between global sea level and ''hyperthermal'' intervals, potentially because of the melting of small alpine ice sheets on Antarctica, thermal expansion of seawater, or both. However, the early onset of sea level rise relative to the CIE of the PETM suggests contributions from other mechanisms, perhaps decreasing ocean basin volume, on sea level rise.

The Palaeocene-Eocene thermal maximum (PETM), a period of intense, global warming about 55 million years ago, has been attributed to a rapid rise in greenhouse gas levels, with dissociation of methane hydrates being the most commonly invoked explanation. It has been suggested previously that high-latitude methane emissions from terrestrial environments could have enhanced the warming effect, but direct evidence for an increased methane flux from wetlands is lacking. The Cobham Lignite, a recently characterized expanded lacustrine/mire deposit in England, spans the onset of the PETM and therefore provides an opportunity to examine the biogeochemical response of wetland-type ecosystems at that time. Here we report the occurrence of hopanoids, biomarkers derived from bacteria, in the mire sediments from Cobham. We measure a decrease in the carbon isotope values of the hopanoids at the onset of the PETM interval, which suggests an increase in the methanotroph population. We propose that this reflects an increase in methane production potentially driven by changes to a warmer and wetter climate. Our data suggest that the release of methane from the terrestrial biosphere increased and possibly acted as a positive feedback mechanism to global warming.

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 δ 18 O 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 Pacifi c 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 defi ned by fl uctuations in the sand (>63 μm) component, occurring on a wavelength of ~1 m, corresponding to Milankovitch-scale frequency. Analyses of foraminifer oxygen isotopic (δ 18 O) and Mg/Ca composition, combined with TEX 86 analyses from organic carbon, are used to generate records of seawater temperature and oxygen isotopic composition (δ 18 O SW ). 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 δ 18 O SW 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.