Changes in solute chemistry of Yangtze headwaters following the 2008 Wenchuan earthquake: Does seismicity influence silicate weathering fluxes?

Abstract:

Large earthquakes may directly connect tectonic activity and chemical fluxes because they trigger landslides that supply fresh minerals for chemical weathering, at the same time that earthquakes and landslides influence the hydrological pathways that regulate solute production. But connections between earthquakes and continental dissolved chemical fluxes have yet to be clearly observed. Here we show increases in the concentration of silicate-derived dissolved ions and in the dissolved ⁸⁷Sr/⁸⁶Sr isotopic ratios in the Min Jiang (Yangtze river, with >20,000 km² basin area) following the 2008 Wenchuan earthquake along the eastern margin of the Tibetan Plateau. Specifically, we find large changes in the Na/Ca ratio of the dissolved load of the Min Jiang that represent a ~4x increase in the flux of cations from chemical weathering of silicate minerals above pre-earthquake values. We suggest that this change reflects a significant, earthquake-driven increase in the silicate-derived alkalinity that removes carbon dioxide from the ocean-atmosphere system over geologic timescales. Post-earthquake changes in Min Jiang solute chemistry extend beyond the region of co-seismic landslide activity, suggesting that large-scale hydrologic changes inferred for this earthquake play at least a significant role in driving the observed hydrochemical patterns. Our new empirical evidence demonstrates that a large earthquake can substantially alter river solute chemistry at the continental scale and thus points to a potential mechanistic link between tectonic activity, which regulates earthquake frequency, and fluxes of alkalinity from weathering.