Alkenone

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Alkenones are highly resistant organic compounds (ketones) produced by phytoplankton of the class Prymnesiophyceae.[1]

The structure of a 37:3 alkenone, (8E,15E,22E)-heptatriaconta-8,15,22-trien-2-one, C37H68O

The exact function of the alkenones remains under debate although they may be storage lipids.[2]

Coccolithophoroids, for instance Emiliania huxleyi, respond to changes in water temperature by altering the production of long-chain unsaturated alkenones in the structure of their cell. At higher temperatures, more of the di-unsaturated molecules are produced than tri-unsaturated [3] The molecules are resistant to diagenesis, and can be recovered from sediments up to 120 million years old.[4]

The ambient water temperature in which the organisms dwelt can be estimated from ratio of their unsaturated alkenones (C37-C39) that are preserved in marine sediments. The modified Unsaturation Index of “di” versus “tri” unsaturated C37 alkenone is calculated according to the following relationship from,[3] which is modified after the original Unsaturation Index from [5] that included the tetra-unsaturated alkenone:

UK37 = C37:2/(C37:2 + C37:3)

The Unsaturation Index can then be used to estimate the water temperature according to the following experimental relationship:[3]

T [°C] = (UK37 - 0.039)/0.034

References[edit]

  1. ^ Marlowe, I.T., Green, J.C., Neal, A.C., Brassell, S.C., Eglinton, G. and 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, 203-216 doi:10.1080/00071618400650221
  2. ^ Eltgroth, M.L., Watwood, R.L., and Wolfe G.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
  3. ^ a b c Prahl, F.G. and Wakeham, S.G. (1987) "Calibration of unsaturation patterns in long-chain ketone compositions for palaeotemperature assessment." Nature 330, 367-369 doi:10.1038/330367a0
  4. ^ Brassell S.C., M. Dumitrescu, and ODP Leg 198 Shipboard Science Party (2004) "Recognition of alkenones in a lower Aptian porcellanite from the west-central Pacific." Organic Geochemistry 35, 181-188 [1]
  5. ^ Brassell, S.C., Eglinton, G., Marlowe, I.T., Pflaumann,U. and Sarnthein, M. (1986) "Molecular stratigraphy: a new tool for climatic assesment" Nature 320, 129-133 doi:10.1038/320129a0
  • Bradley, S R. (1999) Paleoclimatology: Reconstructing Climates of the Quaternary. Second edition. Academic Press