Coccolithophores numbers

A number of factors are thought to influence the transformation of living coccolithophores from the surface ocean into the sedimentary record, many of which have an important bearing on the fossil record (see review by Baumaim et al. 2005). These include incorporation into fast sinking marine snow , breakage and dissolution due to grazing. 

CoccoUthophores produce long-chain alkenones that have proved particularly useful for palaeo-temperature reconstruction they can be found in almost all marine sediments from the present day back to at least 140 million years, and are remarkably unaffected during sedimentation and burial. It turns out that in order to maintain the flexibility of their cell membranes, coccolithophores alter the number of double bonds in the alkenone chain in response to temperature. Laboratory experiments using cultures of Emiliani huxleyi have shown that the relative abundance of alkenones containing 37 carbon atoms and two double bonds (C37 2) is higher in cooler waters, while the relative abundance of alkenones containing 37 carbon atoms and three double bonds (C37-3) is higher in warmer waters (Prahl Wakeham 1987). The alkenone unsaturation index, Ul, is thus defined as ... 

Many details are still obscure, and data are only available from a limited number of species, but it appears that most coccolithophores alternate between fully armored (heterococcolith-covered) diploid life stages and less-well-armoured (either holococcolith-covered or else naked) haploid phases. Both phases are capable of indefinite asexual reproduction, which is rather unusual among protists. That sexual reproduction also occurs fairly frequently is evidenced by the observation of significant genetic diversity within coccolithophore blooms. Bloom populations do not consist of just one clone... 

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