Two coccolithophores collected from 15 m depth in the Gulf of California in July 2004. On the left is Emiliania huxleyi and on the right is Gephyrocapsa oceanica. SEM image from Patrizia Ziveri (Universitat Autonoma de Barcelona, Spain).
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Increasing Atmospheric CO2, Coccolithophores and Fisheries
Before the Industrial Revolution, atmospheric CO2 concentrations remained relatively constant for 400,000 years. Since then the concentrations have almost doubled. Future atmospheric CO2 is projected to double again by the year 2100. Much attention has been focused on the impact of increasing atmospheric CO2 levels on global temperature. Many efforts are focusing on ocean environments as a possible carbon sink to offset the increase in CO2. Of particular interest are coccolithophores; these organisms are important bloom forming plankton with hard scales made of calcium carbonate (CaCO3, basically limestone). Coccolithophores live at the sea surface, removing both CO2 and bicarbonate from the seawater thereby taking up carbon. When they shed their scales, die, or are eaten, the scales sink providing transport of carbon to depth. However, increasing atmospheric CO2 also changes the ocean pH. When atmospheric CO2 dissolves in seawater, it reacts with the water producing carbonate, bicarbonate and hydrogen ions. The increase in hydrogen ions decreases the ocean pH, making it more acidic. This encourages CaCO3 (the coccolithophore scales) to dissolve, which makes them (and hence the carbon) unable to sink. The communities on the floor of the deep sea are reliant on the transport of carbon resources from the upper ocean for survival. These benthic communities survive on small margins of food availability, so any disturbance that shrinks those margins could be disastrous. Benthic communities are particularly important to humans because of the large groundfish, shellfish, and bivalve fisheries they support. While the CaCO3 compounds themselves are not used as a food resource for benthic organisms, they provide the necessary dense ballast to get carbon out of the upper ocean and down to the sea floor. The decrease of CaCO3 production in the upper ocean will decrease the amount of carbon available to benthic communities.
- feature story by Katie Watkins |
