Detecting climatic signals in an anthropogenically disturbed catchment: The late-Holocene record from the Petit Lac d’Annecy, French Alps

Abstract

Historical and documentary records from the Petit Lac d’Annecy, indicate that human activities have been the dominant ‘geomorphic process’ shaping the catchment during the late Holocene, with deforestation, agriculture and artificial drainage profoundly affecting both the pace and spatial distribution of soil erosion. The impact of past climatic change on the evolution of the catchment is less certain because of the lack of long-term climate records for the site. Previous attempts to use the sediment record from the lake to investigate the role past climate change may have played were hampered by the difficulty in isolating and disentangling the climatic signal preserved within the archive, because of overprinting of human activity. This is a common problem in regions with a long history of human activity in the landscape. In this study we use a range of novel statistical techniques (including cross-correlation and cross spectral analysis) to assess the relative importance of climate in driving landscape dynamics. The statistical analysis is carried out on an updated high-resolution palaeo-environmental data set from the Petit Lac d’Annecy. The results of the statistical analysis indicate that regional climate phenomena such as the Atlantic multidecadal oscillation are partly responsible for landscape dynamics at Petit Lac d’Annecy throughout the late Holocene. We find that the Petit Lac d’Annecy catchment typically requires decades, or longer, to respond to changes in precipitation, reflecting the stochastic nature of river sediment storage and transport. The use of a 4 yr integrated lake core record effectively attenuates the ‘signal shredding’ effect of shorter-term internally generated sediment transport processes. Nonetheless, the lake record of climatically induced geormorphic process–responses is weak compared with the pervasive impact of human activities.

Erosion under climate and human pressures: An alpine lake sediment perspective

“…Numerous publications are presenting several thousand yearslong continuous erosion records from low altitude alpine lakes with small-scale (<100 km 2 ) catchment areas (Bajard et al, 2015;Cruise et al, 2009;Czymzik et al, 2013;Dearing et al, 2001;Doyen et al, 2013;Foster et al, 2003;Joannin et al, 2014;Jones et al, 2013;Lauterbach et al, 2012;Manalt et al, 2001;No€ el et al, 2001;Simonneau et al, 2013b;Swierczynski et al, 2013). In those cases, the terrigenous flux or at least the more commonly and more accurately-measured relative terrigenous contribution to the sediment can be obtained.…”

“…Noteworthy is the major research effort in the late 1990's: drilling of Lake Annecy, which generated a large number of papers collected in a 2001 special issue of the Journal of Paleolimnology (Oldfield and Berthier, 2001). However, regarding erosion patterns, Lake Annecy represents a slightly smaller catchment area which does not permit to integrate erosion at a regional scale whereas it developed to be a major site to discuss erosion processes (Dearing et al, 2001;Foster et al, 2003;Jones et al, 2013).…”

“…The onset of high resolution, nondestructive and cost effective investigation tools based on rock magnetic, physical and geochemical sediment properties marked the early 2000's participating in the increasing amount of studied sequences and a better definition of Holocene hydroclimate variability (Arnaud et al, 2005;Bertrand et al, 2007;Chapron et al, 2002;Haug, 2001). However, in areas where human activities deeply shaped the environment for millennia it appeared more and more obvious that reconstructing climate from erosion cannot be successful without understanding the influence of human practices and inversely (Arnaud et al, 2005;Dearing and Jones, 2003;Foster et al, 2003;Giguet-Covex et al, 2014, 2012Jones et al, 2013). As a consequence, climate and land-use changes as well as their impacts upon the erosion cycle must be understood together in order to be able to reconstruct each of them accurately.…”

Geomagnetic and mineral magnetic characterization of the Anthropocene

“…The premise of most mineral magnetic studies of the Holocene is that lake sediments are likely to record details of the interplay between palaeoclimate, ecosystem stability and functioning, and sediment delivery within the catchment of lakes. These linkages are complex and often mostly catchment-specific (Dearing & Jones 2003;Jones et al 2013). Nevertheless, mineral magnetic studies are powerful in discriminating catchment sediment sources (especially topsoils or rock types; Dearing 2000).…”

“…First, the mineral magnetic record of atmospheric particulate pollution related to fossil fuel burning has left behind a strong record of magnetic Fe-oxides in peat bogs (Oldfield et al 1978;Rothwell et al 2005) and lakes (Dearing 1999). Second, deforestation, soil erosion and sediment delivery into lacustrine and marine systems has left behind strong signatures in the mineral magnetic record (Dearing 1999;Dearing & Jones 2003;Mercuri et al 2012;Jones et al 2013). Identification of both these responses has inevitably relied upon using a multi-method approach, one that often involves integrating mineral magnetic, pollen, historical and often chemical data, combined with detailed chronologies.…”