Coccoliths

Biogenic A. Calcareous B. Siliceous >30 >30 48 Foraminifera, coccoliths, calcareous algae, molluscs, bryozoa, and corals 14 Diatoms and radiolaria... 

Many unicellular eukaryotes are free-living cells, but may form huge local communities, which are especially beneficial to the homeostasis of the ocean/atmos-phere carbon cycle, e.g. coccoliths. Many others are not free-living, but are extremely valuable in symbiotic relationship with multi-cellular plants and animals. Unfortunately, some unicellular eukaryotes are the causes of disease, for example Trypanosoma, which are animals and cause sleeping sickness in humans (see Section 8.9 for parallel diseases of plants). These facts are reminders that while we consider that the whole ecosystem works to one general purpose (Section 4.4), this does not exclude the obvious feature that within its overall associations we can see diseases inflicted on one species by another or competition between similar species. Many bacteria are also causes of serious eukaryote diseases. Even so at the end of... 

Cocatalyst heterogenization, 16 87 Cocatalysts, metal alkyls, 12 190 20 153 Cocatalyzed baths, 9 801 Coccidiosis, controlling, 20 139 Coccolith exoskeletons, 24 60 Cochineal, colorant in cosmetics, 7 835 Cochromite, 6 47 It... 

Figure 10. Summary of experimentally determined fractionation factors for Ca isotopes in the formation of foraminifera and coccolith shell carbonate, and for rapid inorganic precipitation of aragonite from an Mg-Ca-Cl solution. Data for the foraminifer G. ornatissima and the coccolith E. huxleyi are from De La Rocha and DePaolo (2000). Data on G. sacculifer are from Nagler et al. (2000). Data for O. universa and aragonite are from Gussone et al. (2003). Two of the forams and the coccolith E. huxleyi have similar fractionation behavior, with an overall fractionation factor of-1 to -1.5%o, and a small temperature dependence of about 0.02 per °C. The foram G. sacculifer appears to have a strongly temperature dependent fractionation factor.

Figure 11. (a) Late Pleistocene 5 Ca record based on measiwe-ments of G. sacculifer (from Nagler et al. 2000). The inferred variations of temperature are similar to diose inferred from variations of Mg/Ca in die same sediment core, (b) Plio-Pleistocene record of seawater b Ca based on bulk coccolith ooze from DSDP Site 590B in the soudiwestem Pacific (Tasman Sea). The 2.5 m.y. record shows only small variations of 5 Ca. The seawater curve is constructed assuming that the fractionation between seawater and bulk sediment remained constant. The decrease of S Ca at ca. 0.7 Ma could reflect cooling rather than a change in the seawater 5 Ca. 

Second in importance to the sedimentary PIC flux are the detrital remains of coccol-ithophorids, a genus of phytoplankton. As shown in Figure 15.1b, these plants deposit calcium carbonate in plates (about 50 per cell) that overlap to create an external shell. An individual coccolithophorid will create and shed these plates on a continual basis at rate of about 1 per hour. The plates also separate from each other after death of the plant, especially if the detrital remains fell into waters that promote dissolution. These plates are referred to as coccoliths and have the crystalline structure of the mineral calotte. 

Coccolithophorids Phytoplankton that deposit calcareous plates called coccoliths. 

Coccoliths Calcareous plates deposited by phytoplankton called coccolithophorids. 

Coccolith, an exo-skeleton of coccolithophores, consists of calcite crystals of uniform size showing a most unusual morphology, which resembles a trug. The structure of the exo-skeleton consists of about thirty calcite crystals of equal size, which are regularly aligned and conjugated. This unusual form of calcite crystals (shown in Fig. 14.5) has stimulated particular interest, and many studies have been conducted on this structure [8]. 

There is no doubt that the Habitus of calcite crystals forming the exo-skeleton of coccoliths is designed naturally to match the function of spicules, but further investigation may be required to explain the growth mechanism of this peculiar form and the relations between R and V crystals. 

Biological calcification processes are widely distributed in nature. They can be found in microorganisms, in plants, in the animal kingdom and in humans. Under physiological conditions, the results of mineral deposition in biological systems can be represented by the formation of bones, teeth and shell material as well as coccoliths, corals, pearls etc. The variety of biomineralisates can best be expressed by the fact that approximately 128,000 species of molluscs636 are known. The majority of them (Conchifera) form shells of different kinds of size and shape as well as of color. 

Emiliania huxleyi is a unicellular alga which is surrounded by a number of loose oval discs of calcium carbonate (coccoliths). It has been shown that the CaC03 of the... 

Coccoliths, and the related scales and sheaths, are characteristic features of a widespread group of organisms. The morphology of each structure is typical of each species and represents a range of extracellular objects from simple mineral-free plates to intrically sculptured, calcified and crystalline units fitted together to make a wreath or incrustation around the cell (for reviews see560,561 ). 

Westbroek, P., De Jong, E. W., Dam, W., Bosch, L. Soluble intracrystalline polysaccharides from coccoliths of Coccolithus huxleyi (Lohmann) Kamptner 1. Calc. Tiss. Res. 12, 227 (1973)... 

Watabe, N. Crystallographic analysis of the coccolith Coccolithus huxleyi. Calc. Tiss. Res. 1, 114(1967)... 

Ca2+ is also bound by certain polysaccharides, for example in coccolith formation by some unicellular organisms. 

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