Introducing Oceanography by David N. Thomas

Author:David N. Thomas
Language: eng
Format: epub
Publisher: Dunedin Academic Press Ltd

Figure 8.7 (C) Foraminifer, Orbulina universa with extended pseudopodia to catch food.

Figure 8.8 (A) Diatoms close up.

Figure 8.8 (B) during spring bloom.

Diatoms can form dense blooms in coastal waters, and are an important food source for protozoan, and especially zooplankton grazers. These blooms can be so dense and extensive that they are easily seen by colour sensors on satellites (see Chapter 14). However, once formed the frustules dissolve very slowly, and some ocean floor sediments are described as diatomaceous or siliceous oozes – massive accumulations of diatom frustules that have sunk from the surface waters. Like the foraminiferal remains described above, these diatom records are prime resources for palaeo-oceanographers for reconstructing past ocean and climate events. Diatomaceous earth can also be mined, and was a key component of the first dynamite invented by Alfred Nobel in 1867.

Diatom blooms are not the only micro-phytoplankton that can be seen from space. The coccolithophores are a group of photosynthetic algal species that are equally beautiful as the diatoms when looked at under the microscope. Instead of being encased in silicate, these single-celled organisms are covered in intricately patterned plates of calcium carbonate (coccoliths). They can also form extensive blooms where the ocean surface turns a milky white. One of the well-known species, Emiliana huxleyi, forms blooms in the north Atlantic covering an area of the ocean equivalent to the size of Great Britain. Due to the highly reflective nature of the white coccoliths, these blooms are easily visible from space, and so can be tracked using satellite imagery. The coccoliths sink and are incorporated into sediments, where they can accumulate, locking up huge amounts calcium carbonate. The impressive chalk ‘white cliffs of Dover’ are largely made up of calcium carbonate from coccolithophores.

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