Another intriguing finding in the Quelccaya record is the discovery of two pronounced peaks in the electrical conductivity and particulate data. Electrical conductivity measurements (ECM) vary
with the acidity of the core sample, providing information on alkaline dust content. Particulate measurements also quantify the amount of dust in a given core layer.
The two pronounced peaks centered at 600 A.D. and 920 A.D. suggest pre-Incan
agricultural activities on the altiplano. While killing frosts occur here even in summer, hardy tubers such as potatoes and cold-adapted chenopods like quinoa are well suited to the altiplano environment. The existence of an extensive pre-hispanic
system of raised fields in this region of the altiplano and the increase in dust inputs evident in the Quelccaya record suggest that pre-Incan peoples may have placed large portions of the altiplano under cultivation with tubers and grains. It is
unlikely that climate change alone could produce such marked signals in the ECM and particulate records; well before the present millennium, it seems, mankind was already making its mark on the Andean environment.
NOAA Paleoclimatology Program and INSTAAR, University of Colorado, Boulder
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