Magnetic measurements recording Late Holocene man‐induced erosion in S. Greenland

Abstract

Magnetic measurements have been carried out on four lake sediment successions in interior S. Greenland. The longest record extends back to 7000 C14 years BP. Based on the magnetic susceptibility six units have been distinguished. The results of the magnetic analyses show a close correlation between the four investigated sites, corroborated by pollen stratigraphy and radiocarbon dates. The period after the deglaciation, lasting for some thousand years, was characterized by sparse vegetation on the unstable soils. Erosion rates were high as revealed by the high concentration of magnetic minerals. Along with the spreading of dwarf‐shrub heaths the soils stabilized, reducing the eroding capacity, and are seen as decreasing concentrations of magnetic minerals in the sediments. During the subsequent period there seems to have been an equilibrium between climate and vegetation resulting in minimal erosion. The arrival of the Norsemen in c. AD 1000, introducing cattle and cutting down the ‘forests’, seems to have caused a disturbance in the fragile environment. It destroyed the attained equilibrium and is seen in the sediment records as an increase in magnetic concentrations. Due to the disappearance of the Norsemen in the 15th century, or slightly later, a new phase of soil stabilization began. A new and still ongoing phase of even more severe soil erosion is connected with the reappearance of man, now as a sheep breeder, in the beginning of this century. Magnetic concentrations are again high, being in the same order of magnitude as during early Holocene time.