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Erosion drives the export of particulate organic carbon from the terrestrial biosphere (POC biosphere ) and its delivery to rivers. The carbon transfer is globally significant and can result in drawdown of atmospheric carbon dioxide (CO 2 ) if the eroded POC biosphere escapes degradation during river transfer and sedimentary deposition. Despite this recognition, we lack a global perspective on how the tectonic and climatic factors which govern physical erosion regulate POC biosphere discharge, obscuring linkages between mountain building, climate, and CO 2 drawdown. To fill this deficit, geochemical (δ 13 C, 14 C and C/N), hydrometric (water discharge, suspended sediment concentration) and geomorphic (slope) measurements are combined from 33 globally-distributed forested mountain catchments. Radiocarbon activity is used to account for rock-derived organic carbon and reveals that POC biosphere eroded from mountain forests is mostly < 1300 14 C years old. Annual POC biosphere yields are positively correlated with suspended sediment yields, confirming results from Taiwan and a recent global analysis, and are high in catchments with the steepest slopes. Based on these relationships and the global distribution of slope angles (3-arc-second), it is suggested that topography steeper than 10° (16% of the continental area) may contribute ~ 40% of global POC biosphere erosional flux. Climate is shown to regulate POC biosphere discharge by mountain rivers, by controlling hydrologically-driven erosion processes. In catchments where discharge measurements are available (8 of the 33) a significant relationship exists between daily runoff (mm day − 1 ) and POC biosphere concentration (mg L − 1 ) ( r = 0.53, P < 0.0001). The relationship can be described by a single power law and suggests a high connectivity between forested hillslopes and mountain river channels. As a result, annual POC biosphere yields are significantly correlated with mean annual runoff ( r = 0.64, P < 0.0001). A shear-stress POC biosphere erosion model is proposed which can explain the patterns in the data. The model allows the climate sensitivity of this carbon flux to be assessed for the first time. For a 1% increase in annual runoff, POC biosphere discharge is predicted to increase by ~ 4%. In steeper catchments, POC biosphere discharge increases more rapidly with an increase in annual runoff. For comparison, a 1% increase in annual runoff is predicted to increase carbon transfers by silicate weathering solute fluxes in mountains by 0.4–0.7%. Depending on the fate of the eroded POC biosphere , river export of POC biosphere from mountains may act as an important negative feedback on rising atmospheric CO 2 and increased global temperature. Erosion of carbon from the terrestrial biosphere links mountain building and climate to the geological evolution of atmospheric CO 2 , while the carbon fluxes are sensitive to predicted changes in runoff over the coming century. [ABSTRACT FROM AUTHOR]

In tectonically active mountain ranges, landslides triggered by earthquakes mobilise large volumes of sediment that affect river dynamics. This sediment delivery can cause downstream changes in river geometry and transport capacity that affect the river efficiency to export this sediment out of the epicentre area. The subsequent propagation of landslide deposits in the fluvial network has implications for the management of hazards downstream and for the long-term evolution of topography over multiple seismic cycles. A full understanding of the processes and time scales associated with the removal of landslide sediment by rivers following earthquakes however, is still lacking. Here, we propose a nested numerical approach to investigate the processes controlling the post-seismic sediment evacuation at the mountain range scale, informed by results from a reach scale model. First, we explore the river morphodynamic response to a landslide cascade at the reach-scale using a 2D modelling approach. The results are then used to describe empirically the evacuation of a landslide volume which avoids using a computationally extensive model in catchments which may have thousands of co-seismic landslides. Second, we propose a reduced-complexity model to quantify evacuation times of earthquake-triggered landslide clusters at the scale of a mountain range, examining the hypothetical case of a M w 7.9 earthquake and its aftershocks occurring on the Alpine Fault, New Zealand. Our approach combines an empirical description of co-seismic landslide clusters with the sediment export processes involved during the post-seismic phase. Our results show that the inter-seismic capacity of the mountain range to evacuate co-seismic sediment is critical to assess the sediment budget of large earthquakes, over one to several seismic cycles. We show that sediment evacuation is controlled by two timescales, 1. the transfer time of material from hillslopes to channels and 2. the evacuation time of the landslide deposits once it has reached the fluvial network. In turn, post-seismic sediment evacuation can either be connectivity-limited, when sediment delivery along hillslopes is the main limiting process, or transport-limited, when the transport by rivers is the limiting process. Despite high values of runoff, we suggest that the Southern Alps of New Zealand are likely to be in connectivity-limited conditions, for connection velocities <10 m.yr−1. Connection velocities >2 m.yr−1 are sufficient to allow most of co-seismic sediments to be mobilised and potentially exported out of the range within less than one seismic cycle. Because of the poorly-constrained rate of sediment transfer along hillslopes, our results potentially raise the issue of co-seismic sediment accumulation within mountain ranges over several seismic cycles and of the imbalance between tectonic inputs and sediment export. We, therefore, call for renewed observational efforts to better describe and quantify the physical processes responsible for the redistribution and mobilization of sediment from landslide scars and deposits. [ABSTRACT FROM AUTHOR]