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Linking the lithogenic, atmospheric, and biogenic cycles of silicate, carbonate, and organic carbon in the ocean.
- Source :
- Biogeosciences Discussions; 2009, Vol. 6 Issue 4, p6579-6599, 21p, 2 Charts, 3 Graphs
- Publication Year :
- 2009
-
Abstract
- Geochemical theory describes long term cycling of atmospheric CO<subscript>2</subscript> between the atmosphere and rocks at the Earth surface in terms of rock weathering and precipitation of sedimentary minerals. Chemical weathering of silicate rocks takes up atmospheric CO<subscript>2</subscript>, releases cations and HCO<subscript>3</subscript><superscript>-</superscript> to water, and precipitates SiO<subscript>2</subscript>, while CaCO<subscript>3</subscript> precipitation consumes Ca<superscript>2+</superscript> and HCO<subscript>3</subscript><superscript>-</superscript> and releases one mole of CO<subscript>2</subscript> to the atmosphere for each mole of CaCO<subscript>3</subscript> precipitated. At steady state, according to this theory, the CO<subscript>2</subscript> uptake and release should equal one another. In contradiction to this theory, carbonate precipitation in the present surface ocean releases only about 0.6 mol of CO<subscript>2</subscript> per 10 mole of carbonate precipitated. This is a result of the buffer effect described by ψ, the molar ratio of net CO<subscript>2</subscript> gas evasion to net CaCO<subscript>3</subscript> precipitation from seawater in pCO<subscript>2</subscript> equilibrium with the atmosphere. This asymmetry in CO<subscript>2</subscript> flux between weathering and precipitation would quickly exhaust atmospheric CO<subscript>2</subscript>, posing a conundrum in the classical weathering and precipitation cycle. While often treated as a constant, ψ actually varies as a function of salinity, pCO<subscript>2</subscript>, and temperature. Introduction of organic C reactions into the weathering-precipitation couplet largely reconciles the relationship. in the North Pacific Ocean central gyre rises from 0.6 to 0.9, as a consequence of organic matter oxidation in the water column. records the combined effect of CaCO<subscript>3</subscript> and organic reactions and storage of 20 dissolved inorganic carbon in the ocean, as well as CO<subscript>2</subscript> gas exchange between the ocean and atmosphere. Further, in the absence of CaCO<subscript>3</subscript> reactions, ψ would rise to 1.0. Similarly, increasing atmospheric pCO<subscript>2</subscript> over time, which leads to ocean acidification, alters the relationship between organic and inorganic C reactions and carbon storage in the ocean. Thus, the carbon reactions and can cause large variations in 25 oceanic carbon storage with little exchange with the atmosphere. [ABSTRACT FROM AUTHOR]
- Subjects :
- SILICATES
CARBONATES
CATIONS
PRECIPITATION (Chemistry)
WEATHERING
OCEAN temperature
Subjects
Details
- Language :
- English
- ISSN :
- 18106277
- Volume :
- 6
- Issue :
- 4
- Database :
- Complementary Index
- Journal :
- Biogeosciences Discussions
- Publication Type :
- Academic Journal
- Accession number :
- 71738940
- Full Text :
- https://doi.org/10.5194/bgd-6-6579-2009