Coccolithophores: Tiny Algae That Shape Ocean Chemistry

Published: 2025-12-25

Coccolithophores are unicellular marine algae that produce intricate calcite platelets called coccoliths. Despite their microscopic size — typically 5 to 15 micrometers in diameter — they are major contributors to the global carbon cycle, producing an estimated 1.5 billion tonnes of calcite annually.

The most abundant species, Emiliania huxleyi, forms massive blooms visible from space, turning vast areas of ocean a milky turquoise. These blooms influence ocean albedo, dimethyl sulfide production, and the vertical flux of carbon to the deep sea.

Fossil coccoliths, or calcareous nannofossils, are essential biostratigraphic markers. Their rapid evolution and global distribution make them ideal for dating and correlating marine sedimentary sequences. The chalk cliffs of Dover, for example, are composed almost entirely of Cretaceous coccoliths.