This article is about alkenone biomolecules having applications in paleothermometry. For the class of organic compounds in general, see Enone.
Alkenones are long-chain unsaturated methyl and ethyl n-ketones produced by a few phytoplankton species of the class Prymnesiophyceae.[1] Alkenones typically contain between 35 and 41 carbon atoms and with between two and four double bonds.[2] Uniquely for biolipids, alkenones have a spacing of five methylene groups between double bonds, which are of the less common E configuration. The biological function of alkenones remains under debate although it is likely that they are storage lipids.[3][4] Alkenones were first described in ocean sediments recovered from Walvis Ridge[5] and then shortly afterwards in cultures of the marine coccolithophore Gephyrocapsa huxleyi.[6] The earliest known occurrence of alkenones is during the Aptian 120 million years ago.[7] They are used in organic geochemistry as a proxy for past sea surface temperature.
The chemical structure of a 37:3 alkenone, (8E,15E,22E)-heptatriaconta-8,15,22-trien-2-one, C37H68O
Alkenone-producing species respond to changes in their environment — including to changes in water temperature — by altering the relative proportions of the different alkenones they produce. At higher temperatures more saturated alkenones are produced proportionally. This means that the relative degree of unsaturation of alkenones can be used to estimate the temperature of the water in which the alkenone-producing organisms grew.[8] The relative degree of unsaturation as first described (UK37) included the tetra unsaturated C37 alkenone:
However, a simplified Unsaturation Index (UK′37), generally more useful in marine settings, is based on di- versus tri- unsaturated C37 alkenones and defined as:
UK′37 = C37:2/(C37:2 + C37:3) [9]
The UK′37 can then be used to estimate sea surface temperature according to an empirical relationship determined from core-top calibrations. The most commonly used calibration is that of Müller et al., 1998:
UK′37 = 0.033T [°C] + 0.044 [10]
The Müller et al. (1998) calibration is not suitable for all environments and, in particular, different calibrations are required for high latitudes and lacustrine settings.
^Marlowe, I.T.; Green, J.C.; Neal, A.C.; Brassell, S.C.; Eglinton, G.; Course, P.A. (1984). "Long chain ( n -C37–C39) alkenones in the Prymnesiophyceae. Distribution of alkenones and other lipids and their taxonomic significance". British Phycological Journal. 19 (3): 203–216. doi:10.1080/00071618400650221.
^Rontani, Jean‐François; Prahl, Fredrick G.; Volkman, John K. (2006). "RE‐EXAMINATION OF THE DOUBLE BOND POSITIONS IN ALKENONES AND DERIVATIVES: BIOSYNTHETIC IMPLICATIONS". Journal of Phycology. 42 (4): 800–813. doi:10.1111/j.1529-8817.2006.00251.x. S2CID 84316762.
^Epstein, B.L.; d'Hondt, S.; Hargraves, P.E. (2001). "The possible metabolic role of C37 alkenones in Emiliania huxleyi". Organic Geochemistry. 32 (6): 867–875. Bibcode:2001OrGeo..32..867E. doi:10.1016/S0146-6380(01)00026-2.
^Eltgroth, Matthew L.; Watwood, Robin L.; Wolfe, Gordon V. (2005). "PRODUCTION AND CELLULAR LOCALIZATION OF NEUTRAL LONG‐CHAIN LIPIDS IN THE HAPTOPHYTE Algae ISOCHRYSIS GALBANA AND EMILIANIA HUXLEYI". Journal of Phycology. 41 (5): 1000–1009. doi:10.1111/j.1529-8817.2005.00128.x. S2CID 22092773.
^De Leeuw, J.W.; v.d. Meer, F.W.; Rijpstra, W.I.C.; Schenck, P.A. (1980). "On the occurrence and structural identification of long chain unsaturated ketones and hydrocarbons in sediments". Physics and Chemistry of the Earth. 12: 211–217. Bibcode:1980PCE....12..211D. doi:10.1016/0079-1946(79)90105-8.
^Volkman, J.K.; Eglinton, G.; Corner, E.D.S.; Sargent, J.R. (1980). "Novel unsaturated straight-chain C37C39 methyl and ethyl ketones in marine sediments and a coccolithophore Emiliania huxleyi". Physics and Chemistry of the Earth. 12: 219–227. Bibcode:1980PCE....12..219V. doi:10.1016/0079-1946(79)90106-X.
^Brassell, Simon C.; Dumitrescu, Mirela (2004). "Recognition of alkenones in a lower Aptian porcellanite from the west-central Pacific". Organic Geochemistry. 35 (2): 181–188. doi:10.1016/j.orggeochem.2003.09.003.
^ abBrassell, S. C.; Eglinton, G.; Marlowe, I. T.; Pflaumann, U.; Sarnthein, M. (1986). "Molecular stratigraphy: A new tool for climatic assessment". Nature. 320 (6058): 129–133. Bibcode:1986Natur.320..129B. doi:10.1038/320129a0. S2CID 4366905.
^Prahl, F. G.; Wakeham, S. G. (1987). "Calibration of unsaturation patterns in long-chain ketone compositions for palaeotemperature assessment". Nature. 330 (6146): 367–369. Bibcode:1987Natur.330..367P. doi:10.1038/330367a0.
^Müller, Peter J.; Kirst, Georg; Ruhland, Götz; von Storch, Isabel; Rosell-Melé, Antoni (1998). "Calibration of the alkenone paleotemperature index U37K′ based on core-tops from the eastern South Atlantic and the global ocean (60°N-60°S)". Geochimica et Cosmochimica Acta. 62 (10): 1757–1772. doi:10.1016/S0016-7037(98)00097-0.
Alkenones are long-chain unsaturated methyl and ethyl n-ketones produced by a few phytoplankton species of the class Prymnesiophyceae. Alkenones typically...
last 16,000 years from records of planktonic stable oxygen isotopes and alkenone unsaturation ratios". Palaeogeography, Palaeoclimatology, Palaeoecology...
temperature calibration of the alkenone unsaturation index (U K′ 37 ) in surface waters and comparison with surface sediments: ALKENONE UNSATURATION INDEX". Geochemistry...
terminations) of older glacial periods. Temperature-sensitive lipids, long chain alkenones, found in lake and marine sediments, are well-regarded as a powerful paleothermometer...
articles on Historic and Prehistoric climate indicators of all types. To Add: Alkenone analysis TEX-86 analysis Nile river flood levels Trace mineral ratios in...
compounds, known as alkenones, can be found in marine sediments long after other soft parts of the organisms have decomposed. Alkenones are most commonly...
research, amongst other sedimentological studies, geochemical studies, with alkenones, Mg/Ca, and micropaleontological, with foraminifera, pollen and spores...
characteristic of certain climatic zones. Biomarker molecules such as the alkenones may yield information about their temperature of formation. Chemical signatures...
the middle of the Mesozoic Era. An analysis of CO2 reconstructions from alkenone records shows that CO2 in the atmosphere declined before and during Antarctic...
Several geochemical proxy tools include long-chain organic molecules (e.g. alkenones), stable and radioactive isotopes, and trace metals. Additionally, sediment...
bankruptcy in 2015. By 2015, cultivation of fatty acid methyl esters and alkenones from the algae, Isochrysis, was under research. By 2016, Thomas Brueck...
into the icehouse climate. Multiple proxies, such as oxygen isotopes and alkenones, indicate that at the Eocene–Oligocene transition, the atmospheric carbon...
A paleothermometer is a methodology that provides an estimate of the ambient temperature at the time of formation of a natural material. Most paleothermometers...
with palaeoglacier presented. As for ocean sediments, the variations of alkenone levels and faunal abundances were measured to model paleotemperatures in...
composition of alkenones often reflect the isotopic enrichment or depletion of the surrounding environment, and the δD values of alkenones in different...
for jet biofuels. By 2015, cultivation of fatty acid methyl esters and alkenones from the algae, Isochrysis, was under research as a possible jet biofuel...
Sonzogni C. Interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry. Nature 385, 707-710 (1997). Bard E, Arnold M, Maurice...
Andreas Mackensen; Kimitaka Kawamura; Richard D. Pancost (15 March 2010). "Alkenone and boron-based Pliocene pCO2 records". Earth and Planetary Science Letters...
"Enhanced climate variability during the last millennium recorded in alkenone sea surface temperatures of the northwest Pacific margin". Global and Planetary...
the summer thermocline. and for its production of molecules known as alkenones that are commonly used by earth scientists as a means to estimate past...
University of Washington 2015 The Greenhouse Emiliania huxleyi Coccolithophore Alkenone production, Algal blooms 167.7 Mb 38,554 Joint Genome Institute 2013 The...
considerations (especially δ18O); the Mg/Ca ratio of foram tests, and alkenones, are also useful. Often, many are used in conjunction to get a multi-proxy...
estimates off the West African coast through biochemical indicators known as alkenones (Sachs 2005) Warming of the subsurface ocean in the subpolar North Atlantic...
diagenetically altered (e.g. planktonic foraminifera) or absent (e.g. alkenones). TEX86 has been extensively used to reconstruct Eocene (55-34Ma) SST...
the Eocene is published by Evans et al. (2018). A 25-million-year-long alkenone-based record of surface temperature change in the Paleogene from the North...
surface temperatures. This included studying whether the 14C ages of alkenones could be used to estimate paleotemperature, as lateral transport can cause...
environmental changes over the last 600 years. These reconstructions are based on alkenones, Membrane lipids and stable isotope ratios of globigerinoides ruber. It...
of the Horn of Africa. They took cores of marine sediment, testing for alkenones, and concluded that about 70,000 years ago this region experienced a change...
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