NATURAL "SEQUESTRATION" OF ATMOSPHERIC CARBON BY WEATHERING OF KENTUCKY'S CARBONATE MINERALS

Interactions between the atmosphere and Kentucky's abundant carbonate rocks create a significant atmospheric carbon sink. This (originally) atmospheric carbon leaves Kentucky as dissolved inorganic carbon, primarily bicarbonate, via the Ohio River. Recent field measurements within the 25 km² Cave City basin of the south central Kentucky karst area indicate that of the 7.8x10³±1.9x10³ kg ha^-1 of total inorganic carbon (TIC) leaving the basin over one year, 1% entered the aquifer as recharge, 42% was produced by biological activities (originally as atmospheric carbon), and 57% was derived from carbonate mineral dissolution within the landscape/aquifer system. For comparison, the rate of the atmospheric carbon loss from this process is roughly 50 times that of the projected sequestration rate at Kentucky's Paradise Fossil Plant Carbon Sequestration Test Site.

The ratio of TIC derived from "old" mineral carbon to that from "young" atmospheric carbon of 57:43 is in contrast to published estimates of continental carbonate mineral weathering CO₂ sink terms that have typically assumed that each mole of old mineral carbon reacts with one mole of young carbon as H₂CO₃* for a 50:50 ratio. Examination of the kinetics of the CaCO₃-H₂O-CO₂ system suggests that details of atmospheric CO₂/carbonate mineral interactions may have some dependence on the kinetics of the dissolution and precipitation reactions. The often-assumed overall balance between the continental CO₂ sink (from weathering of carbonate minerals) and the oceanic CO₂ source (from an equal amount of carbonate mineral precipitation) may thus not be in balance to the extent that the kinetics of the reactions are influenced by varying geochemical environments.

We are currently 1) collecting data at several locations in Kentucky during 2001-02 to add organic carbon fluxes to our model, and to quantitatively evaluate impact of strong acids, and 2) expanding our carbon dynamics monitoring network to California (alpine) and southern China (subtropical) to begin to understand climatic influences on these processes.