How hot? Comparing palaeo-thermometers

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Temperature reconstructions are among the most important sources of information in palaeo-environmental research. Enclosed marginal seas like the Mediterranean and Red Sea provide a disproportionately broad spectrum of information in palaeo-environmental studies, because they record changes with a high signal-to-noise ratio. Unfortunately, studies of these regions, where salinities are high, can suffer from major problems with using conventional methods for estimating past temperatures. Notably, Mg/Ca ratios in microfossil shells and organic geochemical measures such as alkenone unsaturation ratios can be problematic.

Other organic geochemical methods have been proposed (e.g., Tex86: Trommer, G. et al., Millennial scale variability in Red Sea circulation in response to Holocene insolation forcing. Paleoceanography, 25, PA3203, doi:10.1029/2009PA001826, 2010.; Trommer, G. et al., Sensitivity of Red Sea circulation to sea level and insolation forcing during the last interglacial. Climate of the Past, 7, 941-955, 2011), and other inorganic methods as well (e.g., clumped isotopes).

In addition, elemental mapping with scanning electron microscopes has indicated that Mg/Ca may not work in a whole-shell approach, but could be made to work in a targeted approach. For example, see: Hoogakker, B.A.A. et al., Mg/Ca paleothermometry in high salinity environments. Earth and Planetary Science Letters, 284, 583-589, 2009. Also, laser-ablation approaches have given some promising results (e.g., Ni Fhlaithearta, S. et al., Reconstructing the sea floor environment during sapropel formation using trace metals and sediment composition. Paleoceanography, 25, PA4225, doi:10.1029/2009PA001869, 2010).

Our group has a perfect and very large set of sample material to evaluate the different approaches relative to each other. Also, at the RSES we have most of the required equipment, or we have effective collaboration relationships with other groups for specialised analyses that we cannot perform in house.

With geochemically oriented candidates, we can therefore set up unique experiments for novel inter-comparison of a variety of methods for palaeotemperature reconstruction in challenging environments. Depending on the candidate’s specific interests, this work could focus in several specific directions, and an appropriate supervision team will be ‘custom-built’ to best cover those interests.

Do you have a knack for geochemistry, and the enthusiasm and tenacity to help us crack this nut, and obtain internationally highly relevant results? Then get in touch (Prof. Eelco J Rohling)!

We can support projects on this topic at Honours, MSc, and PhD level.


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