Alkenone
Encyclopedia
Alkenones are highly resistant organic compounds (ketone
s) 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 di-unsaturated molecules are produced than tri-unsaturated [Prahl and Wakeham]. The molecules are resistant to diagenesis
, and can be recovered from sediments up to 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 [Prahl and Wakeham], which is modified after the original Unsaturation Index from [Brassell et al] that included the tetra-unsaturated alkenone:
The Unsaturation Index can then be used to estimate the water temperature according to the following experimental relationship [Prahl and Wakeham]:
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
s) produced by phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
of the class Prymnesiophyceae
Prymnesiophyceae
Prymnesiophyceae is a haptophyte class. Although it was originally described by Casper in 1972, it did not receive a Latin diagnosis until Hibberd provided one in 1976....
.
The exact function of the alkenones remains under debate.
Coccolithophoroids, for instance Emiliania huxleyi
Emiliania huxleyi
Emiliania huxleyi, often abbreviated "EHUX", is a species of coccolithophore with a global distribution from the tropics to subarctic waters. It is one of thousands of different photosynthetic plankton that freely drift in the euphotic zone of the ocean, forming the basis of virtually all marine...
, 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 [Prahl and Wakeham]. The molecules are resistant to diagenesis
Diagenesis
In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration and metamorphism. These changes happen at relatively low temperatures and pressures...
, and can be recovered from sediments up to 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 [Prahl and Wakeham], which is modified after the original Unsaturation Index from [Brassell et al] that included the tetra-unsaturated alkenone:
- UK′37 = C37:2/(C37:2 + C37:3)
The Unsaturation Index can then be used to estimate the water temperature according to the following experimental relationship [Prahl and Wakeham]:
- T [°C] = (UK′37 - 0.039)/0.034