A 2500 year record of natural and anthropogenic soil erosion in South Greenland

Charly Massa (1) , Vincent Bichet (1) , Emilie Gauthier (1) , Bianca Perren (1) , Olivier Mathieu (2) , Christophe Petit (3, 4, 5) , Fabrice Monna (6) , Jacques Giraudeau (7) , Rémi Losno (8) , Hervé Richard (1)

1 LCE - Laboratoire Chrono-environnement (UMR 6249)
2 BGS - Biogéosciences [UMR 6282]
3 ArScAn - Archéologies et Sciences de l'Antiquité
4 UP1 UFR03 - Université Paris 1 Panthéon-Sorbonne - UFR Histoire de l'art et archéologie
5 Archéologies environnementales
6 ARTeHiS - Archéologie, Terre, Histoire, Sociétés [Dijon]
7 EPOC - Environnements et Paléoenvironnements OCéaniques
8 LISA (UMR_7583) - Laboratoire Interuniversitaire des Systèmes Atmosphériques

The environmental impact of the Norse landnám in Greenland has been studied extensively. But to date, no study has quantified the soil erosion that Norse agricultural practices are believed to have caused. To resolve this problem, a high resolution sedimentary record from Lake Igaliku in South Greenland is used to quantitatively reconstruct 2500 years of soil erosion driven by climate and historical land use. An accurate chronology allows for the estimation of detritic fluxes and their uncertainties. Land clearance and the introduction of grazing livestock by the Norse around 1010 AD caused an acceleration of soil erosion up to 8 mm/century in 1180 AD which is two-fold higher than the natural pre-landnám background. From 1335 AD to the end of the Norse Eastern Settlement (in the mid-fifteenth century), the vegetation began to recover from initial disturbance and soil erosion decreased. After an initial phase of modern sheep breeding similar to the medieval one, the mechanization of agriculture in the 1980s caused an unprecedented soil erosion rate of up to 21 mm /century, five times the pre anthropogenic levels. Independently, a suite of biological and geochemical proxies (including Ti and diatom concentrations, C:N ratio, 13C and 15N of organic matter) confirm that the medieval and modern anthropogenic erosion far exceeds any natural erosion over the last 2500 years. Our findings question the veracity of the catastrophic scenario of overgrazing and land degradation considered to have been the major factor responsible for Norse settlement demise. They also shed light on the sustainability of modern practices and their consequences for the future of agriculture in Greenland.

Mots clés: Landnám; Eastern settlement; Soil erosion; Agriculture; Greenland; Norse

Domaines: Interfaces continentales, environnement; Milieux et Changements globaux

Charly Massa, Vincent Bichet, Emilie Gauthier, Bianca Perren, Olivier Mathieu, et al.. A 2500 year record of natural and anthropogenic soil erosion in South Greenland. Quaternary Science Reviews, 2012, 32, pp.119-130. ⟨10.1016/j.quascirev.2011.11.014⟩. ⟨hal-00648503⟩