Coccolithophores coccoliths

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]. 

Meldrum, 2002), the elaborately shaped spicules in ascidians, and finely the sculpted coccolith shells in coccolithophores (Mann, 2001). For silica structure, the diatoms produce the most exquisite siliceous cell wall (Sumper and Brunner, 2006). Also the calcium phosphate in bone shows a highly regulated organization and arrangement. Interestingly, avians have two main biomineralization systems, one produces calcium carbonate for egg shell and the other produces calcium phosphate for bone (Bauerlein, 2000 Mann, 2001). 

Roth P. H. (1994) Distribution of coccoliths in oceanic sediments. In Coccolithophores (eds. A. Winter and W. G. Siesser). Cambridge University Press, Cambridge, UK, pp. 199-218. 

Particulate Calcium in WCR 82-B. Calcium is a major component of particulate matter and occurs largely as calcite (5). Most particulate Ca is small and is predominantly present in 10-20-jLtm sized coccolithophores in surface waters and in 1-5- im sized coccoliths below the euphotic zone (5). Individual coccoliths sink only fractions of a meter per day (2, 5). Hence, the <53-fim Ca concentration in waters below 100 m would be expected to show the least temporal variability of all particulate elements sampled. For this reason, Ca data from below 100 m was used for comparison of samples collected with GF and MQ filters and by the LVFS and MULVFS. 

Coccolithophores synthesize different types of coccoliths during different life-cycle stages. Here we concentrate on the heterococcoliths associated with the diploid life stage. These heterococcoliths are formed from crystal units with complex shapes, in contrast to holococcoliths which are constructed out of smaller and simpler crystal constituents. Coccoliths are typically synthesized intracellularly (within a vesicle), probably one at a time, and subsequently extruded to the cell surface. The time taken to form a single coccolith can be less than 1 h for E. huxleyi. Coccoliths continue to be produced until a complete coccosphere covering (made up of maybe 20 coccoliths, depending on species) is produced. 

Most coccolithophores construct only as many coccoliths as are required in order to provide a... 

Coccolithophores, in common with other phytoplankton, experience only an ephemeral existence. Typical life spans of phytoplankton in nature are measured in days. Comparison of the rate at which CaCOs is being produced in open ocean waters (as measured by the rate of uptake of isotopically labeled carbon), to the amounts present (the standing-stock ), has led to the calculation that the average turnover (replacement) time for CaC03 averages about 3 days, ranging between a minimum of <1 and a maximum of 7 days at different locations in the Atlantic Ocean. This implies that if a surface-dwelling coccolithophore synthesizes coccoliths on a Monday, the coccoliths are fairly unlikely to still be there on the Friday, either because they have redissolved or else because they have sunk down to deeper waters. 

Following death, some of the coccolith CaCOs dissolves in the surface waters inhabited by coccolithophores, with the rest of the coccolith CaCOs sinking out of the surface waters within zooplankton fecal pellets or marine snow aggregates. The exact means by which some coccoliths are dissolved in near-surface waters are unclear (dissolution within zooplankton guts may be important), but regardless of mechanisms several lines of evidence suggest that near-surface dissolution does occur. The size of... 

Bi L, Yang P Impact of calcification state on the inherent optical properties of Emiliania huxleyi coccoliths and coccolithophores, J Quant Spectrosc Radiat Transf 155 10—21, 2015. 

Coccolithophores are, with rare possible exceptions, exclusively marine algae, chiefly planktonic although some benthonic forms are known. They secrete minute calcitic plate scales a few microns across. The mineralized plate scales are called coccoliths and may be extremely abundant in some soil parent materials, particularly chalk. Chalk commonly consists almost exclusively of the tests of planktonic foraminifers, discussed below, and coccoliths the two components may be present in approximately equal-weight abundances, or either component may strongly predominate. Although both kinds of fossil are calcitic, they have remarkably different resistance to solution, and local conditions may favor concentration of one or the other type in soils derived from a chalky parent material. A characteristic Cretaceous coccolith is illustrated in Figure 5. 

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