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monsoon region, indicate that climate conditions turned ei-
ther sharply arid or more humid circa 5 ka B.P. [Magny and
Haas, 2004], and records from East Africa suggest increased
aridity around this time [Chalié and Gasse, 2002]. The Soreq
Cave in Israel contains speleothems, which have provided
continuous climate records covering several tens of thou-
sands of years and are shown here (Figure 2d) because of
their proximity to the Kilimanjaro ice core records. As in the
Kilimanjaro ice core record, the Soreq Cave record (Figure
2d) suggests that an abrupt event also occurred in the Middle
East and that it was the most prominent climatic event in the
last 13,000 years [Bar-Matthews et al., 1999; Bar-Matthews
and Ayalon, 2004].
Research at many sites located in extratropical latitudes has
yielded information that unusually cold, but humid, condi-
tions dominated in these areas. The most famous of these
discoveries was
“
Otzi
”
or the
“
Tyrolean ice man,
”
whose
remarkably well-preserved body was discovered in the Alps
in 1991 when it melted out of a retreating glacier (location in
Figure 1). When his remains were radiocarbon dated, it was
discovered that he died (the forensic evidence suggests he
was murdered) and was enclosed in a sudden surge of snow
and ice around ~5200 years ago [Baroni and Orombelli,
1996]. In other locations around the world, vascular plants
are being exposed for the
Whether effective moisture increased or decreased during
this period, there is a consensus among the records that an
abrupt and marked cooling episode occurred. This anoma-
lously cold climate lasted a relatively short time, perhaps a
few decades to a few centuries, before the climate just as
abruptly reverted to its previous state. A possible link to this
temperature excursion is seen in the methane records from
the Greenland and Antarctic ice cores (Figure 2e), which
shows the lowest concentration of this
gas in
the Holocene ~5200 years ago [Chappellaz et al., 1997;
Raynaud et al., 2000], at the same time as the event in the
Kilimanjaro and Soreq Cave records and at a time when NH
insolation was rapidly decreasing. More recent measure-
ments of CO
2
concentrations and
13
C isotopic compositions
in the EPICA Dome C ice core are reported in higher
resolution and with an updated chronology [Elsig et al.,
2009]. In this record, CO
2
shows a steady rise to preindus-
trial values (~280 ppm) after 5600 years B.P. before which
values were ~260 ppm or slightly lower. Although the
declining insolation did not directly drive this abrupt cool-
ing, feedback within the climate system (oceanic, atmo-
spheric, vegetative, and cryospheric) likely ampli
“
greenhouse
”
ed the
gradual solar variations and the small changes in green-
house gas abundances [deMenocal et al., 2000]. However,
whether a decrease in methane contributed to the forcing of
the mid-Holocene abrupt event, or is a consequence of the
cooling, is still not known.
The cultural rami
first time in 5200 years as glaciers
are melting and retreating. The margin of the Quelccaya Ice
Cap in southern Peru has retreated substantially since it was
first photographed in 1977, and in 2002, a perfectly preserved
wetland plant deposit, which contained no woody tissue, was
discovered. It was identi
cations of the 5200 years B.P. climatic
shift are also debatable. Weiss and Bradley [2001] argued that
from the archaeological perspective, uncertainty about the
causal linkage between abrupt climate change and societal
collapse is due to chronological imprecision and the uncer-
tain ability of societies to adapt to the abruptness, magnitude,
and duration of environmental change. During the Late Uruk
period (~5200 years B.P.), societies in southern and northern
Mesopotamia collapsed [Postgate, 1986; We i s s , 2003]. Con-
comitantly, severe drought was hypothesized to have been
responsible for settlement urbanization in southern Mesopo-
tamia around 5200 years B.P. [Nissen, 1988]. Coincident or
not, this was around the time that some Mesopotamian cul-
tures flourished [Rothman, 2004]. Meanwhile, two civiliza-
tions on opposite sides of the world created calendars at this
time; the Mesoamericans began their long-count calendar in
ed as Distichia muscoides, which
today grows in the valleys below the ice cap and was radio-
carbon dated at ~5200 years B.P. [Thompson et al., 2006a].
This is strong evidence that this ice cap has not been smaller
than its present size for over
five millennia. As the glacier
continues to retreat, more plants have been collected and
radiocarbon dated, and almost all of these con
rm these
original
findings [Buffen et al., 2009]. Other paleoclimate
evidence of this event has been discovered in North America.
For example, trees preserved underwater along the southern
margin of Lake Tahoe in the Sierra Nevada Range suggest an
immersion date of about 5000 years B.P. The preserved
condition of the trees indicates that the water in the lake has
remained high thereafter [Lindstrom, 1990].
18
O record
Figure 2.
(opposite) Various Holocene records showing (a) changing tropical Northern Hemisphere summer insolation; (b) the
δ
18
O ice core record (as 50 year averages), in which
the time series from 4.2 ka B.P. to the present is a composite of Northern Ice Field isotopic records; (d) the
(as 100 year averages) from the Huascar
á
in ice core, northern Peru; (c) the Kilimanjaro
δ
18
O record from the Soreq Cave
(Israel) speleothem; and (e) the polar ice core methane records. The demarcation at ~5.2 ka B.P. divides the early Holocene
δ
“
Hypsithermal
”
18
O values, and more depleted
18
O speleothem values from the late
as characterized by higher insolation, more enriched ice core
δ
δ
Holocene
during which insolation and ice core isotopic values were lower and speloethem isotopic ratios were higher. This
line also marks an archeological horizon in Peruvian prehistory and the onset of the
“
Neoglacial
”
“
modern
”
El Ni
ñ
o
-
Southern Oscillation.
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