Rodent (Abrocoma, Lagidium, Phyllotis) middens collected from 2350 to 2750 m elevation near Arequipa, Peru (16°S), provide an ∼9600-yr vegetation history of the northern Atacama Desert, based on identification of > 50 species of plant macrofossils. These midden floras show considerable stability throughout the Holocene, with slightly more mesophytic plant assemblages in the middle Holocene. Unlike the southwestern United States, rodent middens of mid-Holocene age are common. In the Arequipa area, the midden record does not reflect any effects of a mid-Holocene mega drought proposed from the extreme lowstand (100 m below modern levels, >6000 to 3500 yr B.P.) of Lake Titicaca, only 200 km east of Arequipa. This is perhaps not surprising, given other evidence for wetter summers on the Pacific slope of the Andes during the middle Holocene as well as the poor correlation of summer rainfall among modern weather stations in the central Andes-Atacama Desert. The apparent difference in paleoclimatic reconstructions suggests that it is premature to relate changes observed during the Holocene to changes in El Niño Southern Oscillation modes.
Bibliographical noteFunding Information:
We thank M. Betancourt, J. Dohrenwend, C. Latorre, H. Paisley, and C. Placzek for field assistance; A. Cano for logistical support and permission to sample herbarium specimens at the Museo de Historia Natural in Lima; J. Dohrenwend for map support; M. Dillon for assistance in determining plant flowering seasons; O. Davis for valuable comments; the Instituto Nacional de Recursos Natural (INRENA) for permission to collect plant and other samples in Peru; Geochronology Laboratory for conventional 14C dates; and the University of Arizona National Science Foundation (NSF) Accelerator Facility for accelerator mass spectrometry 14C dates. This study was supported by an Inter-American Institute grant to J. L. Betancourt and V. Markgraf and a NSF grant to J. Quade and J. L. Betancourt.
- Atacama Desert