FLUVIAL-AEOLIAN COUPLING IN SIGNAL BUFFERING: THE ROLE OF THE THAR DESERT IN SEDIMENT FLUX TO THE INDIAN OCEAN

The Indus is the dominant river of SW Asia and its submarine fan can potentially be used to reconstruct the changing state of erosion in the western Himalaya and Karakoram. The composition of the river is known to change quickly during glacial cycles in response to changes in monsoon rainfall intensity. Recently budgets suggest that around half of all the sediment reaching the delta since the start of the Holocene is recycled from terraces, with mountain valleys being the primary source of buffering. However, the role of recycling through the Thar Desert has so far been ignored. In the Indus flood plains fluvial and aeolian systems have exchanged sediment over large spatial scales (100s km) since at least 6 ka. Long distance recycling of Indus River sediment by summer monsoon wind northeastward into the Thar Desert is important enough that the desert shows dominantly lower Indus sediment provenance. Sediments in the Indus lower reaches and delta have had similar zircon U-Pb age populations, feldspar Pb isotope characteristics and Nd isotopic compositions as downwind Thar Desert sand since the mid-Holocene (<4 ka). On smaller spatial scales (1–10 m) there is also stratigraphic evidence of fluvial and aeolian sediment reworking from more local river sources. Summer monsoon winds recycle sediment from the Indus delta northeastward, i.e., upstream, back into the desert. Thus, since the Mid-Holocene, when the desert expanded and the river sediment load decreased because of a weakening summer monsoon, fluvial-aeolian recycling has become an important but little recognized process buffering sediment flux to the ocean. Similar fluvial-aeolian coupling likely also affects sedimentary signal transfer in other dryland regions globally.