Reverse weathering reactions

Inputs and outputs of calcium, magnesium, and carbon can be balanced for the modern ocean. This balance necessitates reverse weathering reactions in the ocean system in which CO2 consumed in weathering on land is released to the ocean-atmosphere system during the formation of minerals in the ocean. If this were not the case, regardless of juvenile emissions of CO2 to the ocean-atmosphere system, atmospheric CO2 concentrations could be reduced to vanishingly small values in less than 5000 years. 

Ristvet B. (1978) Reverse weathering reactions within recent nearshore marine sediments, Kaneohe Bay, Oahu. Test Directorate Field Command, Kirtland AFB, New Mexico, 314 pp. 

Evolution of thinking about the importance of reactions between seawater and detrital clay minerals has come full circle in the past 35 years. Reverse weathering reactions were hypothesized in very early chemical equilibrium and mass balance (Mackenzie and Garrels, 1966) models of the oceans. Subsequent observations that marine clay minerals generally resemble those weathered from adjacent land and the discovery of hydrothermal circulation put these ideas on the back burner. Recent studies of silicate and aluminum diagenesis, however, have rekindled awareness of this process, and it is back in the minds of geochemists as a potentially important process for closing the marine mass balance of some element (see chapter 2). 

The imbalance in the K+ budget and small imbalances in other budgets may be nullified by a number of processes. One possibility is the concept of reverse weathering reactions . In reverse weathering, highly degraded clay minerals react with cations, HCOf and silica in seawater to form complex clay mineral-like silicates. An example reaction addressing the K+ problem would be ... 

This reaction shows that reverse weathering is exactly opposite to continental weathering reactions, which consume C02 and liberate I ICO, (see Section 4.4.3). Experimental studies with Amazon delta sediments in the mid 1990s have provided the first evidence that reverse weathering reactions occur naturally. The K+ sink in Amazon continental shelf sediments alone is calculated to be 6.8 X 1012 gyr-1, representing about 10% of the annual global K+ river flux to the oceans. 

In a similar way, the coexistence of kaolinite, smectite, and quartz fix the ratio (Na )/(H ). Although Sillen s predicted data agree very well with the cation ratios of ocean water, it has not been possible to prove that these "reverse weathering" reactions between clay minerals and quartz take place to a significant extent. The interaction between clay minerals and ambient water is complicated and therefore difficult to study under natural conditions. 

Recently, much attention has been given to reverse-weathering reactions (kaolinite + illite + H ) and aluminosilicate-carbonate reactions (of... 

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