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Alkenones are highly resistant organic compounds (ketones) produced by phytoplankton of the class Prymnesiophyceae. The exact function of the alkenones remains under debate.

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 more stable tri-unsaturated molecules are produced^{[citation needed]}. 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 Unsaturation Index of “di” versus “tri” unsaturated C₃₇ alkenone is calculated according to the following relationship [Prahl, F.G. & Wakeham]:

U^K′₃₇=[C_37:2]/[C_37:2+ C_37:3]

The Unsaturation Index can then be used to estimate the water temperature according to the following experimental relationship^{[citation needed]}:

T (^οC) = (U^K′₃₇ - 0.039) / 0.034

[edit] References

Bradley, S R. (1999) Paleoclimatology: Reconstructing Climates of the Quaternary. Second edition. Academic Press

Prahl, F.G. & Wakeham, S.G. (1987) Calibration of unsaturation patterns in long-chain ketone compositions for palaeotemperature assessment, Nature 330, 367-369

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