Direct measurement of the combined effects of lichen, rainfall, and temperature on silicate weathering

A key uncertainty in models of the global carbonate-silicate cycle and long -term climate is the way that silicates weather under different climatologi c conditions, and in the presence or absence of organic activity. Digital i maging of basalts in Hawaii resolves the coupling between temperature, rain fall, and weathering in the presence and absence of lichens. Activation ene rgies for abiotic dissolution of plagioclase (23.1 +/- 2.5 kcal/mol) and ol ivine (21.3 +/- 2.7 kcal/mol) are similar to those measured in the laborato ry, and are roughly double those measured from samples taken underneath Lic hen. Abiotic weathering rates appear to be proportional to rainfall. Dissol ution of plagioclase and olivine underneath lichen is far more sensitive to rainfall. Copyright (C) 1999 Elsevier Science Ltd.