Global ocean carbonate and carbon dioxide production; the role of reef Foraminifera

Institut und Museum fuer Geologie und Palaeontologie, Tubingen, Federal Republic of Germany

Although coral reefs occupy only 0.17% of the ocean surface, they contribute 900 million tons, or roughly one sixth of the carbonate produced in the world's oceans each year. Corals, coralline algae and foraminifera are by far the most important producers of sediment on reefs. In order to understand the role of foraminifera in reef and global carbonate production cycles, we estimated carbonate production rates of reef foraminifera from more than 70 sites in all oceanic regions. Our first order production estimate shows that reef foraminifera contribute approximately 43 million tons of CaCO ₃ per year, 34 million tons of which accumulate in reef sediments. Eighty percent of the global foraminiferal reef carbonate is estimated to be produced by larger symbiont-bearing species alone. The annual production of 43 million tons represents roughly 0.76 percent of the present-day CaCO ₃ production in the world's oceans and approximately 4.8 percent of the global carbonate reef budget. Given an average weight of 0.5 mg for the typical reef foraminifer, the production of 43 million tons translates into a yearly turnover rate of approximately 86X10 ¹⁵ individuals. The biochemical production of calcium carbonate in the ocean leads to the release of the greenhouse gas CO ₂ which can be discharged into the atmosphere. Using our first order approximation, the annual production of 43 million tons of foraminiferal reef carbonate results in the release of 11.4 million tons of CO ₂ . This represents only 0.05 percent of anthropogenic CO ₂ emission in 1991. On a global scale, both carbonate and CO ₂ production of reef foraminifera are comparatively small. In present-day reef complexes foraminifera do, however, play an essential role in the production of reef carbonates.

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