Deglaciation and Holocene climate change in the western Peruvian Andes

Pollen, charcoal, magnetic susceptibility, and bulk density data provide the first paleoecological record spanning the last 33,000 years from the western cordillera of the Peruvian Andes. Sparse super-puna vegetation existed before 30,000 cal yr B.P. around Lake Compuerta (3950 m elevation), prior to a sedimentary hiatus that lasted until c. 16,200 cal yr B.P. When sedimentation resumed, a glacial foreland or super-puna flora is represented in which Polylepis was a significant element. Glacial outwash, marked by high sedimentary magnetic susceptibility, increased from c.16,200 cal yr B.P. and reached a peak at c. 13,200 cal yr B.P. Between c. 12,500 cal yr B.P. and 10,000 cal yr B.P., magnetic susceptibility was reduced. Vegetation shifts suggest a cool dry time, consistent with regional descriptions of the Younger Dryas event. Deglaciation resumes by 10,000 cal yr B.P. and the last ice is lost from the catchment at ∼7500 cal yr B.P. During the early Holocene warm and dry period between 10,000 and 5500 cal yr B.P., Alnus expanded in downslope forests. Alnus declined in abundance at 5500 cal yr B.P. when wetter and cooler conditions returned and human activity intensified. Maize (Zea mays) pollen first occurred in the core at ∼2600 cal yr B.P., indicating a minimum age for local agriculture. An increase in Alnus pollen abundance at ∼1000 cal yr B.P. could be due to human activity or perhaps due to a regional climate change associated with cultural turnover elsewhere in the Andes at this time.