A Late Holocene record of landscape degradation from Heygsvatn, the Faroe Islands

Abstract

Diatom, magnetic susceptibility and loss-on-ignition (LOI) analyses of a 9-metre sediment core from Heygsvatn (Suðuroy, the Faroe Islands) were used to investigate the response of lake and catchment to mid-Late Holocene environmental change. A 30-lake training set from Faroese lakes was also used to explore the relationships between diatoms and environmental variables and assist in the interpretation of the diatom stratigraphy. Canonical Correspondence Analysis showed that lake depth, light penetration, total phosphorus (TP), pH and dissolved organic carbon (DOC) were the most significant variables affecting diatom distribution in Faroese lakes ( p < 0.06). Nine 14C AMS dates indicated that the sediment record covered the last ~ 5700 years. Exceptionally high rates of sediment accumulation, an increase in LOI and magnetic susceptibility and inversion of radiocarbon dates suggested that a period of elevated soil erosion occurred at Heygsvatn ca. 1700–1200cal. yr. BP. Because this erosion pre-dates the arrival of humans the most likely cause is climate deterioration (cooler, wetter conditions). The diatom stratigraphy supports this hypothesis by showing that during the period of erosion the lake was deeper or/or more depauperate in TP, consistent with the climate becoming wetter and leading to increased lake flushing. Subsequently, with sustained sediment erosion, the lake became more shallow and pH increased as the lake infilled. In combination, the proxies support the idea that the climate became wetter ca. 1700–1200cal. yr. BP in the Faroe Islands, but that the response of the landscape was partly dependent on the increased development of peat initiated during the onset of Neoglacial cooling after 5000cal. years BP.