Abrupt Climate Change: A Paleoclimate Perspective From the World’s Highest Mountains - Abrupt Climate Change: Mechanisms, Patterns, and Impacts - page 212

Figure 1. Locations of sites discussed in the text from which evidence of abrupt climate change has been collected listed as
1 through 12. Ice core sites are shown by circles, sites from which biological evidence was obtained are shown as squares,
marine cores are shown by triangles, speleothems are shown by diamonds, and lakes are shown by water drops. Other ice
core sites mentioned in the text are shown as “ a ” through “ f. ”

climatic events of the middle Holocene are discussed. These
are well documented in several ice core and other proxy
records, the locations of which are shown in Figure 1.

the tropical North Atlantic [Thompson et al., 1995]. The
Holocene has been divided into two climatic regimes: the
early “ Hypsithermal ” (also called the “ Climatic Optimum ” ),
when insolation and average δ

18 O in the ice core records
were highest (indicative of the warmer early Holocene), and
the later “ Neoglacial, ” by which time insolation had declined
to ~60% of the early Holocene high and thereafter decreased
to the present levels. A similar increase in the variability of
concentrations of several chemical species (Cl and SO 4 2
in particular) and insoluble dust was noted in the Sajama ice
cores starting between 5000 and 6000 years B.P. [Thompson
et al., 1998; Bradley et al., 2003]. The division between
these two regimes has been placed in Figure 2 at ~5000 ka
B.P., which is roughly when the frequency of ENSO under-
went a transition to its “ modern ” mode [Abarzua and Mor-
eno, 2008; Moy et al., 2002; Rodbell et al., 1999; Rowe et al.,
2002; Sandweiss, 2003].
It was also around this time (~5.2 ka B.P.) that one of the
most dramatic middle Holocene abrupt climate events

2. ABRUPT CLIMATE EVENTS IN THE HOLOCENE

2.1. The Abrupt Cold Event of 5200 Years B.P.

Solar insolation in the tropical Northern Hemisphere (NH)
increased during the early Holocene as the Earth recovered
from the last glacial stage, peaking at ~9 ka B.P., then
decreasing toward the present (Figure 2a). The shape of this
insolation curve is mimicked by the Holocene records of
δ

18 O from two tropical ice cores: Huascar á in (9°S) in the
Cordillera Blanca of northern Peru (Figure 2b) and Kiliman-
jaro (3°S) in Tanzania, East Africa (Figure 2c). Although
Huascar á in is located in the Southern Hemisphere (SH), its
stable isotope record more closely follows the NH insolation
curve because the predominant source of its precipitation is