Börker, Janine, Hartmann, Jens, Romero-Mujalli, Gibran and Li, Gaojun (2018) Short Communication: Aging of basalt volcanic systems and decreasing CO<sub>2</sub> consumption by weathering. Earth Surface Dynamics . pp. 1-9. DOI 10.5194/esurf-2018-10.

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Abstract

Basalt weathering is one of many relevant processes balancing the global carbon cycle via land-ocean alkalinity fluxes. The CO2 consumption by weathering can be calculated using alkalinity and is often scaled with runoff and/or temperature. Here it is tested if information on the surface age distribution of a volcanic system is a useful proxy for changes in alkalinity production with time.

A linear relationship between temperature normalized alkalinity fluxes and the Holocene area fraction of a volcanic field was identified, using information from 33 basalt volcanic fields, with an r2=0.91. This relationship is interpreted as an aging function and suggests that fluxes from Holocene areas are ~10 times higher than those from old inactive volcanic fields. However, the cause for the decrease with time is probably a combination of effects, including a decrease in alkalinity production from surface near material in the critical zone as well as a decline in hydrothermal activity and magmatic CO2 contribution.

A comparison with global models suggests, that global alkalinity fluxes considering Holocene active basalt areas are ~70% higher than the average from these models imply. The contribution of Holocene areas to the global basalt alkalinity fluxes is however only ~6%, because identified, mapped Holocene basalt areas cover only ~1% of the existing basalt areas. The large trap basalt proportion on the global basalt areas today reduces the relevance of the aging effect. However, the aging effect might be a relevant process during periods of globally, intensive volcanic activity, which remains to be tested.

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