(Table 1) SPM samples and sites along the Rhône Rive

We tested the applicability of the BIT (branched and isoprenoid tetraether) index as a proxy for palaeoflood events in the river-dominated continental margin of the Gulf of Lions (NW Mediterranean). We compared the concentrations of branched glycerol dialkyl glycerol tetraethers (br GDGTs) and crenarchaeol in suspended particulate matter (SPM) collected downstream in the Rhône River, as well as in surface sediments and a ca. 8m piston core from the Rhône prodelta. The core covered the last 400 yr, with four distinct intervals recording the river influence under natural and man-induced shifts in four main channels of the river mouth (Bras de Fer, Grand Rhône, Pégoulier and Roustan). The results indicate that there are mixed sources of br GDGTs and crenarchaeol in the prodelta, complicating application of the BIT index as an indicator of continental organic carbon input and thus as a palaeoflood proxy. However, the sedimentary BIT record for the period when ontinental material was delivered by the river more directly to the core site (Roustan phase; 1892 to the present) mimics the historical paleoflood record. This shows the potential of the BIT index as a palaeoflood proxy, provided that the delivery route of the continental material by rivers to the core sites remains constant over time. The study also highlights the idea that shifts in river channels should be taken into account for the use of the BIT index as a palaeoflood proxy.

本研究针对西北地中海利翁湾以河流为主的陆缘环境，检验了支链与类异戊二烯四醚（branched and isoprenoid tetraether，BIT）指数作为古洪水代用指标的适用性。我们对比了罗讷河下游采集的悬浮颗粒物（suspended particulate matter，SPM）、表层沉积物，以及取自罗讷河前三角洲的约8米长活塞岩心中的支链甘油二烷基甘油四醚（branched glycerol dialkyl glycerol tetraethers，br GDGTs）与泉古菌醇（crenarchaeol）浓度。该岩心覆盖了过去400年的沉积记录，其中存在4个清晰的沉积段，对应河口4条主要河道（铁汊道、大罗讷河、佩古利耶汊道与鲁斯坦汊道）在自然与人为扰动下的河流影响时段。研究结果表明，前三角洲环境中br GDGTs与泉古菌醇的来源复杂多样，这使得BIT指数作为陆源有机碳输入指标、进而作为古洪水代用指标的应用变得复杂化。然而，当陆源物质经由河道直接输送至岩心站位时（鲁斯坦期，1892年至今），沉积记录中的BIT指数序列与历史古洪水记录较为吻合。这表明，只要河流向岩心站位输送陆源物质的路径随时间保持稳定，BIT指数便可作为古洪水代用指标，具备应用潜力。本研究同时强调，在利用BIT指数作为古洪水代用指标时，需将河道变迁纳入考量范围。