North western Alps Holocene paleohydrology recorded by flooding activity in Lake Le Bourget, France

Abstract

A 14-meter long piston core was retrieved from Lake Le Bourget, NW Alps (France), in order to provide a continuous record of flooding events of the Rhone River during the Holocene. The selection of the coring site was based on high resolution seismic profiling, in an area with limited mass wasting deposits and accumulated proximal Rhone River inter-and under-flow deposits. The age-depth model of this core is based on (i) 14 AMS radiocarbon dates, (ii) radionuclide dating ( 137 Cs) and (iii) the identification of historical data (flood events, eutrophication of the lake). The sedimentary record dates back to 9 400 cal BP, and includes a thin mass wasting event deposited around 4500 cal BP. A multi-proxy approach was used to track the evolution and origin of clastic sedimentation during the Holocene, in order to identify periods of higher hydrological activity in the catchment area.Spectrophotometry was used to detect fluctuations in clastic supply and the study of clay minerals (especially the Illite cristallinity index) allowed locating the main source area of fine grained clastic particles settling at the lake after flood events. This dataset highlights up to 12 periods of more intense flooding events over the last 9 400 years in Lake Le Bourget and shows that the main source area of clastic particles during this period is the upper part of the Arve River drainage basin. This part of the catchment area drains several large glaciers from the Mont Blanc Massif, and fluctuations in Rhone River flood supply in Lake Le Bourget is interpreted as resulting essentially from Mont Blanc Glacier activity during the Holocene. The comparison of clastic sedimentation in Lake Le Bourget with periods of increasing land use and periods of Alpine glacier and mid-European lake level fluctuations, suggest that the core LDB04 clastic record in Lake Le Bourget is a continuous proxy of the Holocene hydrological history of the NW Alps.

A spatiotemporal investigation of varved sediments highlights the dynamics of hypolimnetic hypoxia in a large hard‐water lake over the last 150 years

“…Long cores indicate that severe hypoxia did not occur in Lake Bourget over the last 9000 yr, despite many fluctuations in climate and hydrology (Arnaud et al 2005(Arnaud et al , 2012Debret et al 2010). Severe hypoxia has occurred only in the last 80 yr, which indicates clearly that it is a consequence of recent anthropogenic activities and, in particular, of increased nutrient inputs, as shown in other similar lakes (Bü hrer and Ambü hl 2001).…”

Tracking Holocene glacial and high-altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments (Lake Blanc Huez, Western French Alps)

“…Such a climate change at high altitude favoured the development of glaciers at the head of the catchment area as reflected by the increasing content of goethite and FOM in LBH06 (figures 7 and 8). During this period, several more humid and cooler phases were also identified in the Alps by vegetation, glacier and paleohydrological reconstructions based on well-dated sedimentary archives (Haas et al, 1998;Magny, 2004;Vollweiler et al, 2006;Guyard et al, 2007Guyard et al, , 2013Debret et al, 2010). This peak may also partly result from soils erosion induced by the maximal advance of glaciers during the Holocene (ca.…”

“…8500 to 6800 cal BP ( figure 7G) is also matching higher values of L* in LBH06 (figure 7B) reflecting higher clastic supply to LBH. Since glaciers were very limited during the Early Holocene, this signal is interpreted as resulting from relatively colder and wetter conditions at high-altitudes before the onset of cooling abrupt phases also identified in the Alpine realm at lower altitudes based on pollen assemblages, lake levels and large alpine rivers flooding activity (Haas et al, 1998;Magny, 2004;Debret et al, 2010).…”

“…Bourget dated between 9400 and 9700 cal BP and attributed to a large paleo-earthquake (van Rensbergen et al, 1999;Chapron et al, 1996Chapron et al, , 2004Debret et al, 2010;Arnaud et al, 2012). Following the classification of Mulder and Cochonat (1996), SE 1 and SE 11 are interpreted as slide deposits, while SE 9 and SE 10 are graded beds typical from thin distal turbidites.…”

Quantitative historical hydrology in Europe

“…In the River Mosel, the 28 February 1784 flood water level was significantly higher than any other recorded during the past millennium (Sartor et al, 2010), although any discharge estimation should consider that ice jams can raise water levels to much higher elevations than open-water floods (Beltaos, 2008). Other factors enhancing flood severity through time include timing of melting of glaciers (Debret et al, 2010). Global warming is introducing changes in the spatial (latitudinal) and temporal (seasonal) distribution of flooding related to ice and snowmelt (Beltaos and Prowse, 2009).…”