Environmental controls on the brGDGT and brGMGT distributions across the 10 Seine River basin (NW France): Implications for bacterial tetraethers as a proxy for 11 riverine runoff 12

26 Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial lipids that have been 27 largely used as environmental proxies in continental paleorecords. Another group of related lipids, 28 branched glycerol monoalkyl glycerol tetraethers (brGMGTs), has recently been proposed as a 29 potential paleotemperature proxy. Nevertheless, the sources and environmental dependencies of 30 both brGDGTs and brGMGTs along the river-sea continuum are still poorly understood, 31 complicating their application as paleoenvironmental proxies in aquatic settings. In this study, the 32 sources of brGDGTs and brGMGTs and the potential factors controlling their distributions are 33 explored across the Seine