Coccolithophorids

Nanoplankton 2.0 to 20 jjum Protists Mycoplankton Phytoplankton Amoebae, flagellates, Euglenozoa, dinoflagellates Yeasts and fungi Coccolithophorids, Phaeocystis, dinoflagellates ... 

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. 

These shallow-water deposits were the sole source of biogenic carbonate until the evolution and proliferation of planktonic calcifiers, namely the coccolithophorids and the foraminiferans, around 250mybp. This enabled a shift in the site of sedimentary carbonate acciunulation from the shallow waters to the deep sea. At present, about half of the sedimentary carbonates are being buried on the shelves and the other half in the deep sea and slopes. 

In terms of organic carbon generation, the coccolithophorids are a minor player, representing only 6 to 8% of global marine primary production. But their detrital remains contribute disproportionately to the burial of carbon in marine sediments. This is due to near complete loss of POC via remineralization as the detrital hard and soft parts settle to the seafloor. As estimated from Broecker s Box model in Chapter 9, only about 1% of the POM that sinks out of the surfece water is buried in marine sediments. In comparison, about 20% of the biogenic PIC survives to become buried in the sediments. 

Coccolithophorids generate a lot of calcite because they create POC and PIC in a 1-to-l ratio. The overall stoichiometry for these concurrent processes is shown next, illustrating that calcite deposition generates CO2, which is then used to create organic matter. ... 

Prior to the advent of the coccolithophorids and planktonic foraminferans, 200 to 250 miUion years ago, all biogenic calcite precipitation must have been restricted to the shallow waters of the neritic zone. Thus, the evolution of the pelagic calcifiers ushered... 

Coccolithophorids Phytoplankton that deposit calcareous plates called coccoliths. 

Coccoliths Calcareous plates deposited by phytoplankton called coccolithophorids. 

Steemann Nielsen, E. The uptake of free CO2 and HCO3 during photosynthesis of plankton algae with special reference to the coccolithophorid Coccolithus huxleyi. Physiol. 

Manton, I., and Pcterfi, L. S. Observations on the fine structure of coccoliths, scales and the protoplast of a freshwater coccolithophorid, Ilymenomonas roseola Stein, with supplementary observations on the protoplast of Cricosphaera carterae. Proc. Roy. Soc. B. 172, 1-15 (1969). 

Murata A. and Takizawa T. (2002). Impact of a coccolithophorid bloom on the C02 system in surface waters of the eastern Bering Sea shelf. Geophysical Research Letters, 29(11), 1547, doi 10.1029/2001GL013906. 

Weeks S.J. Pitcher G.C. and Bernard S. (2004). Satellite monitoring of the evolution of a coccolithophorid bloom in the Southern Benguela upwelling system. Oceanography, 17(1), 83-89. 

Bramlette M.N. (1958) Significance of coccolithophorids in calcium carbonate deposition. Geol. Soc. Amer. Bull. 69, 121-126. 

Volkman, J.K., Eglinton, G., Corner, E.D.S., and Forsberg, T.E.V. (1980b) Long-chain alkenes and alkenones in the marine coccolithophorid Emiliania hwcleyi. Phytochemistry 19, 2619-2622. 

Diatoms are unicellular, photosynthetic microalgae that are abundant in the world s oceans and fresh waters. It is estimated that several tens of thousands of different species exist sizes typically range from ca 5 to 400 pm, and most contain an outer wall of amorphous hydrated silica. These outer walls (named frustules ) are intricately shaped and fenestrated in species-specific (genetically inherited) patterns5,6. The intricacy of these structures in many cases exceeds our present capability for nanoscale structural control. In this respect, the diatoms resemble another group of armored unicellular microalgae, the coccolithophorids, that produce intricately structured shells of calcium carbonate. The silica wall of each diatom is formed in sections by polycondensation of silicic acid or as-yet unidentified derivatives (see below) within a membrane-enclosed silica deposition vesicle 1,7,8. In this vesicle, the silica is coated with specific proteins that act like a coat of varnish to protect the silica from dissolution (see below). The silica is then extruded through the cell membrane and cell wall (lipid- and polysaccharide-based boundary layers, respectively) to the periphery of the cell. 

A molecular clock has been constructed from our 18S rDNA tree and calibrated with fossil dates from the haptophyte coccolithophorid species (Fig. 4). Our molecular clock calculations indicate... 

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