| Title: | A new organic palaeothermometer for the mid-Cretaceous green-house world |
| Author: | Stefan Schouten |
| Date Submitted: | 04/08/2002 |
| Address: | PO BOX 59
Den Burg
The Netherlands
1790 AB
|
| Phone: | +31 222 369565 |
| Email: | schouten@nioz.nl |
| Co-Authors: | Hopmans, Ellen, C, NIOZ, hopmans@nioz.nl; Sinninghe Damste, Jaap, S, NIOZ, damste@nioz.nl |
| Affiliation: | Netherlands Institute for Sea Research |
| | |
| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725474 |
| Author Homepage: | http://www.nioz.nl |
| Keywords: | proxy, archaea, lipids, hplc, organic geochemistry, temperature CO2 biomarker |
| Abstract: | The mid-Cretaceous earth is often referred to as a "greenhouse" world, i.e. characterised by high atmospheric CO2 levels (estimated to be 3-8 times pre-industrial pCO2), general absence of polar ice caps, reduced temperature gradients from the Equator to the poles, and oceans much warmer than today. Although the green-house climate has received considerable attention as a possible analog for future climate change, there still exists a discrepancy between model-predicted tropical sea surface temperatures (SSTs) exceeding 32°C and considerably lower SSTs derived from del 18-O palaeothermometry on foraminifera. This inconsistency, the "cool tropical paradox," may be related to diagenetic overprinting and inaccuracies in the conversion of del 18-O values into SST. Furthermore, sea surface temperature records in the mid-Cretaceous are sparse and scattered due to the poor preservation of forams. We have recently developed a novel SST proxy based on the membrane lipids of marine crenarchaeota, nannoplankton which thrived in present and past oceans. A study of marine surface sediments from all over the globe showed that these organisms adjust the composition of their tetraether membranes lipids as a response to sea water temperature. This response can be well described by a linear relationship (r2 = 0.92) and thus be used to determine SST from the tetraether membrane composition preserved in sediments. A study of late Quaternary sediments from the Arabian Sea confirms that the tetraether lipids contain a temperature signal. Importantly, a pilot study has indicated that mid-Cretaceous sediments up to the Albian contain these components and that their composition indicate much warmer temperatures for the tropics than present day temperatures (between 5-9°C) and del 18-O palaeothermometry, in line with global circulation model calculations. |
|