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Phoenix666 writes:

The White Cliffs of Dover span England's southeastern coastline for 16 kilometers (10 miles) and reach as tall as 110 meters (350 feet) high. Facing the narrowest part of the English Channel, the cliffs have come to symbolize England since the time of Julius Caesar, often the first and last view travelers have of the country by sea.

The sheer cliffs are composed of white chalk, or calcite, made by coccolithophores – tiny, single-celled algae at the bottom of the marine food chain. Coccolithophores build hard, saucer-shaped calcite plates around themselves that sink and accumulate on the sea floor when the algae die, compacting and hardening into chalk. The White Cliffs' chalk was laid down in a shallow sea above present-day England almost 100 million years ago and thrust upward by movements of the Earth's crust.

Now, researchers outline in a new study the ocean conditions necessary for coccolithophores to flourish, conditions that likely allowed the White Cliffs to form nearly 100 million years ago. The new information comes from an unlikely source: a great bloom of coccolithophores in the Southern Ocean known as the Great Calcite Belt.
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They found coccolithophores depend on concentrations of three key nutrients: nitrate, silicate, and iron. Diatoms need silicate to build glassy shells around themselves, so in areas where silicate was more abundant than nitrate, diatoms outcompeted coccolithophores. Coccolithophores, on the other hand, flourished where nitrate was more abundant than silicate. In these areas there was also enough iron for coccolithophores to thrive, but not enough for diatoms. Coccolithophores also grew better than most diatoms in low-iron regions, according to Balch.

Coccolithophores also flourish where different water masses diverge. At these boundaries, upwelling of deep water brings to the surface trace metals and nutrients coccolithophores need to survive, Balch said.

The upwelling of deep ocean water in the English Channel supplies the necessary nutrients for the lifeforms whose shells compress into chalk over time.

William M. Balch et al. "Factors regulating the Great Calcite Belt in the Southern Ocean and its biogeochemical significance", Global Biogeochemical Cycles (2016). DOI: 10.1002/2016GB005414

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