Limnology and Oceanography e-Books

Smith, Stephen V. 2013. Parsing the Oceanic Calcium Carbonate Cycle: A Net Atmospheric Carbon Dioxide Source, or a Sink?

Stephen V. Smith
Emeritus Professor of Oceanography
University of Hawaii

February 2013
ISBN 978-0-9845591-2-1

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The analysis presented here has two foundation blocks, both literally and figuratively. Coral reefs are iconic examples of the first block: shallow-water calcareous sediment and (eventually) limestone. In his 1842 book From the Voyages of the Beagle, Charles Darwin described the origins of coral atolls as thick limestone deposits from continued reef growth on slowly sinking oceanic seamounts. Besides coral reefs, other shallow, benthic, calcifying communities such as extensive banks dominated by calcareous green algae, oyster reefs, the diverse biotic communities found in temperate-climate kelp beds, also contribute to shallow water calcareous sediment formation.

The second foundation block has been known since the Challenger Expedition of the 1870s: calcareous pelagic sediments that blanket much of the ocean seabed, establishing the clear importance of deep-ocean carbonate deposits. An important aspect of these pelagic sediments is that the percentage of calcium carbonate in these sediments decreases dramatically in water depths greater than 3000-4000 m.

Besides their prominence as major sedimentary deposits in the contemporary ocean, shallow and deep water limestone deposits are found throughout much of the geological record. The comparative roles of shallow versus deep water carbonate sediment and limestone production, dissolution, and accumulation with respect to air-sea exchange of carbon dioxide gas are the subjects of the analysis presented here.

Beyond the scientific foundations of the Beagle and Challenger Expeditions of the 19th Century, more recent scientific papers and reflections on S. V. Smith's own research over the past 40-plus years have drawn attention to some interesting peculiarities in the calcium carbonate reactions, on important differences in net calcium carbonate reactions between pelagic and benthic calcifying systems in the global ocean, and on the carbon dioxide fluxes associated with those systems at the present and recent past, into the near future, over the past interglacial-glacial cycle, and through the geological history of the past 570 million years.

Stephen V. Smith became interested in limestones and limestone formation as a boy collecting rocks and fossils in Central Texas during the 1950's. That interest largely set the direction of his professional career.

He received his BA degree from the University of Texas in 1964, taking Bob Folk’s famous (or infamous) course in carbonate petrology along the way. His MS thesis from Northwestern University (dealing with the petrology of Mississippian limestone mounds in the southwestern Ozark Mountains, under the direction of Larry Sloss; 1966) sharpened his interest in modern carbonate environments and processes. His PhD thesis in Oceanography from the University of Hawaii under Keith Chave (1970) dealt with rates of CaCO3 production in the temperate waters of the Southern California Continental Borderland.

He then studied processes of CaCO3 production in coral reefs and other calcifying environments in the Pacific, Indian, and Southern Oceans, eventually expanding his interests to include organic, as well as inorganic, carbon production and oxidation during 30 years as a faculty member at the University of Hawaii and 8 years as an investigator at the Centro de Investigación Científica y de Educación Superior de Ensenada (Mexico).