Palaeoenvironmental changes during the last ca. 8590 calibrated yr (7800 radiocarbon yr) in the dry forest ecosystem of the Patía Valley, Southern Colombian Andes: a multiproxy approach

Two sediment cores were recovered from two swamps in the dry forest lowland ecosystem of the Patía Valley (Colombia). The 500-cm long core El Patía-1 was analysed using diatoms, pollen, lithostratigraphy, geochemistry, charcoal and radiocarbon dates. The 270-cm long core Patía-2 was analysed using pollen, lithostratigraphy and radiocarbon dates. The environmental reconstruction includes the local development and history of the Patía-1 swamp and the regional vegetation history of the two swamps. The environmental reconstruction shows a fluvial system in the area before 7830 14C yr BP (ca. 8590 cal yr BP). After this date, the river gradually moved away leading to the formation of the swamp Patía-1; open vegetation with patches of dry forest surrounded the swamp. Between 7670 and 6860 14C yr BP (8350-7690 cal yr BP), the swamp become partially isolated from the river and was a permanent water body which was alkaline and mesotrophic. During this period, the surroundings were covered by dry forest. From 6860 to 5870 14C yr BP (7690-6690 cal yr BP), the swamp was totally isolated from the river and suffered from frequent periods of desiccation and erosion. From 5870 to 3570 14C yr BP (6690-3890 cal yr BP), the swamp turned into a marsh/terrestrial environment and in the surrounding area, the dry forest alternated with open vegetation; it is possible that there were human impacts on the environment during this period. Between 3570 and 1990 14C yr BP (3890-2000 cal yr BP), unstable conditions prevailed. After 1990 14C yr BP (2000 cal yr BP), swamp conditions of permanent water were re-established; open vegetation surrounded the swamp. Agriculture and human activities were present and have continued since then. The climatic reconstruction suggests an increase in humidity at ca. 7670 14C yr BP (8350 cal yr BP) and a dry climate between 6860 and 5870 14C yr BP (7690-6690 cal yr BP).