Please join us this Wednesday, December 9th in Hubbs Hall 4500 for our Earth Section Seminar where we will be hearing from Dr. Stephen Smith, Emeritus Professor at the University of Hawaii at Manoa. Please see the talk title and abstract below. Pastries and coffee will be served beginning at 10:30 am, and the talk will begin at 11:00 am.
Dr. Stephen V. Smith
THE ROLE OF CaCO3 REACTIONS IN THE CONTEMPORARY OCEANIC CO2 CYCLE*
The present analysis adjusts previous estimates of global ocean CaCO3 production rates substantially upward, to 133 x 1012 mol yr-1 plankton production and 42 x 1012 mol yr-1 shelf benthos production. The plankton adjustment is consistent with recent satellite-based estimates; the benthos adjustment includes primarily an upward adjustment of CaCO3 production on so-called ?carbonate-poor sedimentary shelves,? and secondarily pays greater attention to high CaCO3 mass (calcimass) and turnover of shelf communities on temperate and polar shelves. Estimated CaCO3 sediment accumulation rates remain about the same as they have been for some years: ~20 x 1012 mol yr-1 on shelves and 11 x 1012 mol yr-1 in the deep ocean.
The differences between production and accumulation of calcareous materials call for dissolution of ~22 x 1012 mol yr-1 (~50%) of shelf benthonic carbonate production and 122 x 1012 mol yr-1 (>90%) of planktonic production. Most CaCO3 production, whether planktonic or benthonic, is assumed to take place in water depths of less than 100 m, while most dissolution is assumed to occur below this depth.
The molar ratio of CO2 release to CaCO3 precipitation (CO2?:CaCO3? ) is less than 1.0 and varies with depth. This ratio, Y, is presently about 0.66 in surface seawater and 0.85 in ocean waters deeper than about 1000 m. The net flux of CO2 associated with CaCO3 reactions in the global ocean in late preindustrial time is estimated to be an apparent influx from the atmosphere to the ocean, of +7 x 1012 mol C yr-1, at a time scale of 102-103 years. The CaCO3 mediated influx of CO2 is approximately offset by CO2 release from organic C oxidation in the water column. Continuing ocean acidification will have effects on CaCO3 and organic C metabolic responses to the oceanic inorganic C cycle, although those responses remain poorly quantified.
*This presentation is based on a paper by the same name, by S. V. Smith and F. T. Mackenzie, available as an ?Online First? publication of Aquatic Geochemistry (v. 21, no. 6, Nov. 2015)