Sediment fluxes and buffering in the post-glacial Indus Basin

The Indus drainage has experienced major variations in climate since the Last Glacial Maximum (LGM) that have affected the volumes and compositions of the sediment reaching the ocean since that time. We here present a comprehensive first-order source-to-sink budget spanning the time since the LGM. We show that buffering of sediment in the floodplain accounts for ca. 20-25% of the mass flux. Sedimentation rates have varied greatly and must have been on average three times the recent, predamming rates. Much of the sediment was released by incision of fluvial terraces constructed behind landslide dams within the mountains, and especially along the major river valleys. New bedrock erosion is estimated to supply around 45% of the sedimentation. Around 50% of deposited sediment lies under the southern floodplains, with 50% offshore in large shelf clinoforms. Provenance indicators show a change of erosional focus during the Early Holocene, but no change in the Mid-Late Holocene because of further reworking from the floodplains. While suspended loads travel rapidly from source-to-sink, zircon grains in the bedload show travel times of 7-14kyr. The largest lag times are anticipated in the Indus submarine fan where sedimentation lags erosion by at least 10kyr.