Geoscience Reference
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Figure 21.6. Geoglyphs, northern Atacama, Chile. (Photo: Mike Smith.)
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S in the Atacama Desert of northern Chile. In order to establish the magnitude of
the radiocarbon reservoir effect, they obtained 14 C ages for different types of sample,
including non-aquatic, carbon-rich sediments. They found that the reservoir effect
ranged from
°
10,700 14 C years. Any uncorrected ages would thus seem
much older than their true age. On the basis of their reservoir corrections, Geyh et al.
( 1999 ) concluded that the humid phase began between 13,000 and 12,000 14 Cyr
BP, while maximum lake levels were reached between 10,800 and 9,200 14 CyrBP.
These results differ from those of Sylvestre et al. ( 1999 ) for the timing of the wettest
phase. A probable reason for these differences is that the lakes and swamps in the
two regions studied were under the influence of air masses that originated from quite
separate sources and were active at quite different times, a conclusion also reached by
Sylvestre ( 2009 ) in her review of LGM climates in South America and by Thompson
et al. ( 2013 ) in their analysis of Andean ice cores.
1,200 to
21.6 Conclusion
The climate of South America is dominated by the easterly summer monsoon in the
tropical north of the continent and by winter westerly air masses in the south of the
continent. As a result, the lands to the west of the central and northern Andes are in
the rain shadow of these very high mountains, while Patagonia in the far south lies in
the rain shadow east of the Andes. The aridity of the Atacama Desert ( Figures 21.4 ,
21.5 and 21.6 ) results from four independent factors: its location in the zone of dry
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