This post is the third in a three-part series on how living creatures use the elements of the periodic table. Read earlier posts here and here, and learn more about the elements on NOVA's two-hour special, "Hunting The Elements."
Calcium (Ca) is all around us and even within us: from rocks to shells, pearls, antacids, bones, teeth (in the form of a mineral appropriately named apatite), nerves, and our beating hearts. Simply reading and thinking about this post requires the shuttling of calcium ions through special calcium-ion channels in our bodies for cardiac muscle contractions and the release of neurotransmitters.
Yet one organism plays a large role in removing calcium from watery environments and trapping it in the form of calcite, which forms rocks. This organism is called a coccolithophore, a photosynthesizing single-celled marine plant.
For the past 230 million years, coccolithophores have been protecting themselves with calcium armor. This armor is made up of hubcap-shaped structures called coccoliths which are composed of calcite molecules, which contain one atom of calcium with one carbon and three oxygen. Each coccolith is just a fraction of a millimeter across, so coccolithophores combine dozens of them to create protective scales, as shown in the image below.
Coccolithus pelagicus. Credit: Richard Lampitt, Jeremy Young, The Natural History Museum, London. Via the Wikimedia Commons and planktonnet.
Over time, these scales flake off into the water, shedding as much as 1.5 million tons of calcite each year. This makes coccolithophores the largest calcite producers in the world's oceans.
Coccolithophores have a complex effect on the biosphere. In the short term, coccolithophores photosynthesize, taking in carbon dioxide from the atmosphere and emitting oxygen. When they create their coccoliths, they take carbon, oxygen, and calcium from the water, removing a carbon atom that could potentially become carbon dioxide. However, in the process of making their coccoliths, they also emit carbon dioxide.
A large-scale effect of coccolithophores is that the carbon used to create the coccoliths is trapped as calcite. When the scales fall off of the organism, the calcite sinks to the ocean floor, where it mixes with silt and clay to form chalk. Over time, the deposits of coccolithophores can accumulate and create geological wonders like the White Cliffs of Dover.
Credit: Remi Jouan, via the Wikimedia Commons
When coccolithophores find the right mixture of sunlight and nutrients, they quickly proliferate, leading to large "blooms." These blooms are so large and dramatic that they even temporarily change the color the local seawater. In this image, taken from space, the calcite scales turn the water brighter and more turquoise, causing it to reflect more sunlight.
A phytoplankton bloom in the Barents Sea. Credit: NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team at NASA GSFC.