Séminaire ISTerre

Quantitative evaluation of the impact of human and climate forcing on erosion in the Alpine Critical Zone over the Holocene

mardi 14 décembre 2021 - 09h45
William Rapuc - ATER, Université Grenoble Alpes, IsTerre, CNRS, Grenoble, France
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The Critical Zone (CZ), defined as the thin active layer at the Earth’s surface is at risk due to climate change and anthropogenic pressure increase. This represents a potential threat to the future of humanity as the CZ is the locus of developing human societies. CZ’s soil erosion is now considered as one of the geosciences/society central issues. Understanding the influence of both forcing factors is key to improve our management of the CZ’s soil resource, especially in mountainous areas where erosion is highest. Only studies combining large spatial and temporal approaches allow to assess the effect of the different forcing factors on soil erosion rates. By applying a retrospective approach based on lake sediments it is possible to reconstruct the long-term evolution of erosion in alpine landscapes. Lake Bourget and Lake Iseo, located in the northern French and Italian Alps, respectively, acts as natural sinks for all the erosion products from their large catchments. Currently, we combined a multiproxy study of lacustrine sediment sections covering the Holocene (Lake Bourget) and the last 2 kyrs (Lake Iseo) with a source-to-sink method, using isotopic geochemistry (εNd, 87Sr/86Sr). The applied methodology allows to disentangle the role of climate and land use as erosion forcing factors through their differential impact on the various rock types present in the catchment. Indeed, high-altitude areas of the two study sites, where the erosion is dominated by precipitation and glacier advances, present isotopic signature different from those of the sedimentary rocks located in the rest of the catchment, where both human activities and precipitations impact erosion through time. To understand the effect of human activities, erosion signals from high-altitude and the rest of the catchment are compared to local and regional erosion chronicles. During the Early Holocene and until 3.8 kyr cal BP, the erosion signal is dominated by climate fluctuations. Since 3.8 kyr, climate fluctuations alone cannot explain measured erosion trends. From then, human activities by modifying the soil erodibility through land-use become the dominant forcing factor of the physical erosion in mountainous environment of the European Alps.

Equipe organisatrice : Organisation labo

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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Sujet : Postdoc sémianire W. Rapuc
Heure : 14 déc. 2021 09:00 AM Amsterdam, Berlin, Rome, Stockholm, Vienne

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