Earthquake-triggered increase in biospheric carbon export from a mountain belt: Insight from the 2008 Mw 7.9 Wenchuan earthquake

Abstract:

Large earthquakes can trigger landslides in mountain belts and erode significant volumes of clastic sediment that is supplied to rivers. Organic carbon eroded by landslides has been viewed as a source of carbon dioxide (CO₂) to the atmosphere, on the basis that organic material is oxidized in the landscape. However, export of this organic carbon by rivers while sediment loads are elevated may instead contribute to a long-term CO₂ sink through sedimentary burial. This process could provide a direct coupling between active tectonics, the carbon cycle and CO₂ drawdown. Despite this recognition, the fate of biospheric carbon eroded by earthquake landslides remains unconstrained.

Here we quantify particulate organic carbon (POC) export in the Zagunao River before and after the 2008 M_w 7.9 Wenchuan earthquake. We use radiocarbon and stable carbon isotopes to correct for rock-derived organic carbon, and we then quantify the flux of POC eroded from the biosphere. We find that biospheric carbon export fluxes doubled in the years following the earthquake, demonstrating the rapid export of earthquake-mobilized carbon by rivers. To examine the decadal impacts, we use measurements until the end of 2011 and a model which considers both particulate organic carbon export and its degradation in the landscape. We estimate that the majority of the earthquake-mobilized organic carbon will be exported by rivers rather than remaining in situ and being oxidized. While the ultimate fate of this material remains to be assessed, enhanced sediment discharge may promote sedimentary burial and long-term preservation. Our findings suggest that erosion of biospheric carbon by earthquake-triggered landslides can directly link active tectonics and mountain building to the drawdown of CO₂.