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 110 million years old.

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 [4] 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., 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