6700 yr sedimentary record of climatic and anthropogenic signals in Lake Aydat (French Massif Central)

Abstract

words)A 19-meter-long sedimentary record retrieved in Lake Aydat (French Massif Central) covers the last 6700 yrs at a high-resolution. A multi-proxy approach (density, magnetic susceptibility, XRF, Rock-Eval, pollen and non-pollen palynomorph analyses and a historical archives study) was used to characterise and propose a model of sedimentation. The high 2 deposition rate results from the combined effects of the high suspension load of the river, autochthonous production and the narrow shape of the incised fluvial valley dammed by a lava flow ca. 8550 years ago. Two contrasted periods (6700±200 -3180±90 cal. BP, and 1770±60 cal. BP-now) were characterized. The lower unit (mid-Holocene) displays a fine and regular lamination and holds a single, major, flood deposit. This unit is capped by an erosive mass wasting deposit triggered ca. 1770±60 cal. BP. The upper unit (late-Holocene) is made of organic rich and fine grained faintly laminated sediment, with numerous interbedded flood deposits and diatom blooms. The sedimentation was principally controlled by climatic forcings until ca. 1100 cal. BP, accompanied by detrital events linked to human activities around the lake. Then, a more detrital input attested by numerous and recurrent flood deposits can be linked to the intensification of a persistent anthropogenic impact on the catchment.Two phases of lake eutrophication are highlighted: 1200-1130 cal. BP, as a result of increased anthropogenic pressure, and the current phase that could have started ca. 150 cal. BP.

Guidelines for Rock–Eval analysis of recent marine sediments

“…It has been increasingly applied to the characterization of organic matter (OM) in soils (Di Giovanni et al, 2000;Disnar et al, 2003;Hetényi et al, 2005;Sebag et al, 2006;Graz et al, 2012;Saenger et al, 2013;Hétényi and Nyilas, 2014), the detection of black carbon (Copard et al, 2006;Poot et al, 2009) and even the analysis of pure organic products (Carrie et al, 2012). It has also been applied for several decades to the study of recent lacustrine sediments (Campy et al, 1994;Di Giovanni et al, 1998;Meyers and Lallier-Vergès, 1999;Ariztegui et al, 2001;Steinmann et al, 2003;Sanei et al, 2005;Jacob et al, 2004;Boussafir et al, 2012;Zocatelli et al, 2012;Lavrieux et al, 2013;Sebag et al, 2013, amongst others) or recent marine sediments (Peters and Simoneit, 1982;Hussain and Warren, 1991;Calvert et al, 1992;Combourieu et al, 1999;Ganeshram et al, 1999;Ozcelik and Altunsoy, 2000;Holtvoeth et al, 2001Holtvoeth et al, , 2003Holtvoeth et al, , 2005Tamburini et al, 2003;Baudin et al, 2007Baudin et al, , 2010Kim et al, 2007;Marchand et al, 2008;Tribovillard et al, 2008Tribovillard et al, , 2009Biscara et al, 2011;…”

Lake Pavin Paleolimnology and Event Stratigraphy

“…In the lower diatomite unit, the development and maturity of beech ( Fagus ) and fi r ( Abies ) woodlands matches the regional climatic variation of the Mid-Holocene toward wetter and cooler conditions (Magny and Hass 2004 ;Lavrieux et al 2013 ). Such conditions also favored the development of vegetation on the shore of Lake Pavin dominated by alder.…”

“…A recent synthesis by Magny et al ( 2013 ) discussed the impact of climate on welldated synchronous phases of lake level changes during the Holocene across Western European mountain ranges or around the Mediterranean Sea, but little is still known about the amplitudes of these lake level changes. Because such lake level reconstructions in Western Europe are typically performed in carbonated lake systems, none of these phases of lake level changes were ever documented in the volcanic area of the French Massif Central during the present interglacial period (Truze and Kelts 1993 ;Chapron et al 2012 ;Lavrieux et al 2013 ). Finally, the outlet of Pavin has been stabilized at an altitude of 1197 m only recently, by the building of human infrastructures at the end of the eighteenth century (Chap.…”

“…The topographic drainage basin of Lake Pavin is presently densely covered by mixed deciduous/coniferous forest (Fig. 23.1 ) compared to nearby environments in this mid altitude region where the vegetation cover has been deeply affected by human activities (and particularly agropastoralism) since the Roman period and the Middle Age (Stebich et al 2005 ;Miras et al 2004 ;Lavrieux et al 2013 ).…”

“…23.12 , they might refl ect larger scale climate shifts. Phases of enhanced precipitation at the onset of the Neoglacial period (between 6000 and 5000 cal BP), during the Bronze Age (between 4300 and 3500 cal BP), at the beginning of the Iron Age (between 2800 and 2600 cal BP) and during the Roman period (around 2000 cal BP) in Lake Pavin might for example match periods of enhanced soil erosion in Lake Aydat (Lavrieux et al 2013 ), higher Rhone River fl ooding activity in Lake Le Bourget (Debret et al 2010 ;Arnaud et al 2012 ), increasing glacier activity in Lake Banc Huez (Simonneau et al 2014 ), phases of higher lakelevels in the Western Europe (Magny 2006 ;Magny et al 2013 ), reactivation of canyons draining into lakes Majeur and Sigriou (Simonneau et al 2013b ) and soil erosion in maar lake Meerfelder (Martin-Puertas et al 2012 ). These clastic input peaks in Lake Pavin could either result from the direct impact of periods of heavy rainfalls on runoff along the steep slopes of the crater rim characterized by numerous gullies and thalwegs (Fig.…”