Holocene climate change and human impact, central Mexico: a record based on maar lake pollen and sediment chemistry

This paper presents multiproxy (pollen, magnetic susceptibility, sediment chemistry) records from two maar crater lakes in the Valle de Santiago of Guanajuato, Mexico: Hoya San Nicolás and Hoya Rincon de Parangueo. Sediment cores from the two sites have basal dates of ca 11,600 and 9600 cal yr BP, respectively. The San Nicolás results show that the lake desiccated several times during the Holocene, and this resulted in the selective destruction of the less resistant pollen types. A comparative analysis of data from both sites indicates that during the earliest Holocene (ca 11,600–9000 cal yr BP) there were short term oscillations of wetter and drier climate; during the early Holocene (ca 9000–5700 cal yr BP) it was on average wetter; during the middle Holocene (ca 5700–3800 cal yr BP) drier; and during the middle to late Holocene (ca 3800–2200 cal yr BP) wetter. Increasing human disturbance during the late Holocene of environment obscures the climatic record. Agricultural activities in the area began as early as ca 5700 cal yr BP and intensified around 2400 cal yr BP.