LAUSR

Abstract The development of the Mekong River, although poorly constrained, plays a key role in our understanding of South China Sea drainage evolution. Here we attempt to improve our understanding of this evolution using a fungal spore record in the southwestern South China Sea at International Ocean Discovery Program (IODP) Site U1433. We present the variety of fungal morphologies extracted from the sediments and investigate their possible relationships with paleoenvironmental changes based on types, concentration and flux changes. Overall, > 30 morphologic types were found and are grouped into three basic assemblages: single-, double- and multi-celled spores. The spore fluxes continuously increase up-section, along with their diversity, although there are strong shorter fluctuations. One notable step in evolution is recorded at ca. 8 Ma. We argue that the trends in fungal flux are mainly linked to the strengthened terrestrial biomass input driven by tectonics rather than paleoclimate change and that this event is mainly linked to onset of the Mekong River in its present location.