International Geologiical Congress - Oslo 2008

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CGC-01 General contributions to climate change

 

Support for greenhouse climate models runs hot and cold in early Paleogene mid-latitude New Zealand

 

C.J. Hollis, GNS Science (New Zealand)
E.M. Crouch, GNS Science (New Zealand)
H.E. Morgans, GNS Science (New Zealand)
J.I. Raine, GNS Science (New Zealand)
E.M. Kennedy, GNS Science (New Zealand)
L. Handley, University of Bristol (United Kingdom)
R.D. Pancost, University of Bristol (United Kingdom)
S. Schouten, Royal Netherlands Institute for Sea Research (Netherlands)
J. Baker, Victoria University of Wellington (New Zealand)
J. Creech, Victoria University of Wellington (New Zealand)
J.C. Zachos, University of California - Santa Cruz (United States)
S. Gibbs, University of Southampton (United Kingdom)
C. Burgess, Cardiff University (United Kingdom)
P. Pearson, Cardiff University (United Kingdom)
M. Huber, Purdue University (United States)
 

 

New evidence from marine sediments in Canterbury Basin, New Zealand, highlights an extreme contrast in temperature between late Paleocene and early Eocene times in the mid-latitude southwest Pacific: consistent with warming by 15°C from cool temperate to tropical conditions within <5 million years. Temperature estimates derived from oxygen isotope and Mg/Ca ratios in well-preserved shells of planktic foraminifera range from 30° to 35°C in lower Eocene calcareous mudstone in the mid-Waipara River section, north Canterbury. The same temperature range is recorded in the same sequence by the membrane lipid sea surface temperature (SST) proxy TEX86. Higher in the mid-Waipara section and also further south in the Canterbury Basin, at Hampden Beach, the same three proxies record gradual cooling of SSTs to 18-25°C by middle Eocene times. The interval of peak warmth is correlated to the early Eocene climatic optimum and is associated with incursions of warm water molluscs and larger foraminifera into Canterbury Basin.
In contrast, upper Paleocene glauconitic mudstone in the mid-Waipara section contains only sparse poorly preserved calcareous microfossils, which are unsuitable for paleotemperature analysis. The organic content is suitable for TEX86 analysis, which reveals much cooler SSTs of 17-20°C and is consistent with the scarcity of warm-water indicators within the marine biota.
The New Zealand terrestrial vegetation record also indicates pronounced warming from temperate to a subtropical or tropical climatic conditions through the Paleocene-Eocene transition. The first warm-climate indicators appear in the latest Paleocene, e.g. Nypa pollen, prior to the Apectodinium dinoflagellate acme associated with the Paleocene-Eocene thermal maximum (PETM). Near the onset of the EECO, there is a rapid change from the temperate gymnosperm-rich floras of Paleocene type to subtropical-tropical, Casuarina-dominated, angiosperm-rich floras typical of the Early Eocene. During middle Eocene, a return to warm temperate conditions is evident from an increase in Nothofagus pollen and a decline in megathermal taxa.
Modelled ocean circulation patterns and sea temperatures under early Paleogene greenhouse conditions (600-4000 ppm CO2), predict temperate conditions for the southwest Pacific region around New Zealand, i.e. cooler than 25°C, which is consistent with Paleocene paleotemperature estimates and also with middle Eocene estimates. However, paleontological and geochemical indicators for tropical conditions in the early Eocene imply that the role of ocean currents or other unknown mechanisms, such as tropical cyclones, in poleward heat transport under hyper-greenhouse conditions is much greater than is allowed for in existing coupled ocean-atmosphere circulation models.

 

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