Geoscience Reference
In-Depth Information
subsiding air along the southern limb of the Hadley Cell; the presence offshore of a
cold ocean current and cold upwelling ocean water; its distance from the easterly air
masses that bring rain to Amazonia; and its location in the rain shadow of the Andes.
The Atacama was already arid more than 30 million years ago and may have been dry
for some 150 million years, making it the oldest extant desert on earth. The Neogene
uplift of the Andes occurred in stages, with prolonged intervals of stability punctuated
by phases of relatively rapid uplift. Uplift accelerated in the mid- to late Miocene,
causing major changes in erosion, sedimentation, climate and vegetation. The late
Pliocene and Quaternary climates were marked by rapid fluctuations in temperature
and precipitation and multiple glacial advances and retreats in the high Andes and
Patagonian Andes. Glacial maxima were broadly synchronous in both hemispheres.
Lake fluctuations have been hard to date precisely because of large reservoir effects
but appear to show cold and relatively dry conditions in much of the tropical north
during the Last Glacial Maximum, in contrast to the relatively moist but still very cold
conditions in the centre and south.
