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<p>WTBootstrap: New Instance Uk37</p> <p><b>New page</b></p><div>=== Uk37 ===<br /> <br /> The C37 alkenone unsaturation index ( U_{37}^{k'} ) is a firmly established tool for past sea surface temperatures reconstruction and is based on the relative abundance of di- (C37:2) and tri- (C37:3) unsaturated ketones with 37 carbon atoms. The index varies between 0 and 1, thus it may saturate in the temperature extremes as it becomes more challenging to determine since C37:3 and C37:2 alkenones approach their detection limits. Since alkenones come exclusively from a few species of haptophyte algae which require sunlight, alkenone thermometry offers the advantage of direct estimate of near-surface ocean temperatures. The ubiquitous presence of alkenone-synthesizing organisms (most commonly the coccolithophorids Emiliania huxleyi and Gephyrocapsa oceanic through the world's ocean and the rapidity and high-precision of the alkenone analyses had made U_{37}^{k'} a valuable proxy for paleoceanographic reconstructions.<br /> <br /> However, the U_{37}^{k'} proxy is subject to non-temperature effects, such as lateral transport through oceanic currents (Ohkouchi et al. (2002)) and preferential post-depositional oxidation of C37:3 compared to C37:2 [1] [2]. Furthermore, changes in the seasonality of the proxy (i.e., which part of the seasonal cycle the proxy is recording) may bias the inferred temperatures toward winter or summer conditions [3]. Finally in oceanic regions where the photic zone extends below the surface mixed layer, the sedimentary signal may not strictly represent sea surface temperatures but rather a composite temperature of the mixed layer and the thermocline [4][5].<br /> References<br /> <br /> [1] Hoefs, M. J. L., Versteegh, G. J. M., Rijpstra, W. I. C., de Leeuw, J. W., &amp; Damsté, J. S. S. (1998). Postdepositional oxic degradation of alkenones: Implications for the measurement of palaeo sea surface temperatures. Paleoceanography, 13(1), 42-49. doi:10.1029/97pa02893<br /> <br /> [2] Ohkouchi, N., Eglinton, T. I., Keigwin, L. D., &amp; Hayes, J. M. (2002). Spatial and temporal offsets between proxy records in a sediment drift. Science, 298(5596), 1224-1227. doi:10.1126/science.1075287<br /> <br /> [3] Herfort, L., Schouten, S., Boon, J. P., &amp; Sinninghe Damsté, J. S. (2006). Application of the TEX86 temperature proxy in the southern North Sea. Organic Geochemistry, 37, 1715-1726.<br /> <br /> [4] Müller, P. J., Kirst, G., Ruhland, G., von Storch, I., &amp; Rosell-Melé, A. (1998). Calibration of the alkenone paleotemperature index U_{37}^{k'} based on core-tops from the eastern South Atlantic and the global ocean (60°N-60°S). Geochimica et cosmochimica acta, 62, 1757-1772.<br /> <br /> [5] Prahl, F. G., Mix, A. C., &amp; Sparrow, M. A. (2006). Alkenone paleothermometry: biological lessons from amrine sediment records off Western South America. Geochimica and Cosmochimica Acta, 70, 101-117.<br /> <br /> &lt;!-- Do not edit below this unless you know what you are doing --&gt;<br /> [[Category:OrganicIndex]]</div>

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