Biology Reference
In-Depth Information
centuries-long El Niño- and La Niña-like periods that eerily parallel the
rise and fall of these and other pre-Incan cultures” (2002, 84). A fi nding of
special interest for Holocene ecosystem history is that between the annual
layers of 1490 and 1880 there is evidence of a cold period corresponding to
the Little Ice Age even at this equatorial latitude. Similar cores have been
retrieved from Tibet and Kilimanjaro that give a global perspective to the
fi ndings. Today, there are about 160,000 mountain glaciers, and multispec-
tral satellite data from the LandSat Thematic Mapper (TM) show that be-
tween 1985 and 1999, a set of 930 glaciers in the Swiss Alps lost 18 percent
of their former area at a rate seven times higher than between 1850 and
1973 (Paul et al. 2004).
Events at the transition between the late Pliocene and the early to middle
Pleistocene are recorded in the Canoa Formation of coastal central Ecuador
from stable isotope studies of fossil fi sh, otoliths, mollusks shells, benthic
foraminifera, and shark teeth (Pellegrini and Longinelli 2008). An interest-
ing hypothesis is that there was a north to south migration of cold temper-
ate fi sh from southern North America (e.g., California) to coastal Ecuador
as a result of the closing of the Panama seaway. The idea is that the closure
caused coastal upwelling of cold waters, like that noted in chapter 7 for the
middle Pliocene Paraje Solo Formation of southeastern Mexico, and this
afforded a migratory pathway of suitable water temperatures for cool to
cold-water fi sh.
A number of innovative studies are being made in the high Central Andes
(Betancourt et al. 2000; Baker et al. 2001; Grosjean et al. 2003; Placzek
et al. 2006; Placzek et al. 2009; Theissen et al. 2008). They show that the
dry lake beds on the Altiplano of Bolivia, for example, the Salar de Uyuni
(fi g. 8.6), have repeatedly fi lled up and dried out since 120 kyr. Between
120 and 98 kyr, the now dry lakes were 80 m deep; at 95-20 kyr there was
intermittent shallowing; then between 18.1 and 14.1 kyr there developed
“the deepest and largest lake in the basin” (140 m; Placzek et al. 2006). If
such profound changes were happening during the last glacial-interglacial
cycle, surely they must have occurred on multiple occasions during the past
2.6 million years.
In Argentina and Chile, the Quaternary vegetation and climatic history
often involves subtle shifts in shrubs, herbs (especially grass), and trees
(especially
Nothofagus
) under the infl uence of the meandering Antarctic
anticyclone high pressure system. At the glacial maxima, this system cov-
ered an area about double that of the interglacials and shifted northward
by around 10° latitude. There was a Younger Dryas cold interval, a mid-
Holocene warm/dry period, and a Little Ice age.
