Magnetic susceptibility (MS) was measured with high resolution (5 mm) on a 9 m long, 14C dated core from Lake Le Bourget (Savoie, France), spanning the last 7200 years. The strong correlation (R=0.85) of the MS with the silicate-borne suite of elements (Si, Al, Fe, Mg, K) and anti-correlation with the carbonate content (R =-0.87) allows it to be used as a proxy for the fluctuations of the abundance of riverborne clastic fraction versus authigenic carbonates in sediment. As the Rhône is the only river bringing a significant amount of silicate minerals to the coring site, the MS downstream is interpreted as a proxy of the Rhône suspended load discharge in Lake Le Bourget. This is confirmed over the last 3000 years by the good match with the evolution of hydrological activity of the Rhône as it is known through geomorphological studies of well-dated archaeological sites. Over the last 7200 years, the record is consistent with the regional record of lake water-level fluctuations. While the intensity of the MS signal might be widely affected by the human impact on soil stability, the timing of the period of enhanced hydrological activity appears to be mostly climate-related, and should thus constitute a first step toward a high-resolution (< 8 yr) continuous history of hydrological conditions in the NW Alps.

Two twin-cores (LDB 0101 and LDB 0102) were taken using an Uwitec® coring device on site I (45044.848'N; 5050.891'E) of the ECCHYMOSE 2001 coring survey. Each synthetic core is composed of a succession of three cores. The second core succession was shifted by 2 m in sediment depth and about 5 m in position, in order to ensure the continuity of the record. Cores were cut into < 2 m sections, split, described and stored at 4°C.

Supplement to: Arnaud, Fabien; Revel, M; Chapron, Emmanuel; Desmet, Marc; Tribovillard, N (2005): 7200 years of Rhône river flooding activity in Lake Le Bourget, France: a high-resolution sediment record of NW Alps hydrology. The Holocene, 15(3), 420-428