Long term carbon export from mountain forests driven by hydroclimate and extreme event driven landsliding.

Abstract

The export of organic carbon from terrestrial ecosystems by erosion may play a central role in balancing the geological carbon cycle and Earth's climate over millennial timescales. However, constraints on organic carbon yields have come from sampling modern rivers that don't capture variation over decades to millennia driven by changing hydroclimate and erosion during extreme events. Here we use volumetric reconstructions of lake sedimentary fills to generate timeseries of sediment and organic carbon yields from two catchments draining the Southern Alps, New Zealand over the last millennium. The reconstructed yields indicate that earthquake-induced landslides significantly increase sediment and organic carbon yields, contributing to pulsed export that accounts for ~40% of the total. Between extreme events, organic carbon export increased twofold during centuries with a wetter reconstructed climate. Our findings suggest that the link between hydroclimate and organic carbon export may act as a negative feedback in the longer-term carbon cycle.