Geoscience Reference
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marine organisms. James Kennett and his research group analyzed the
fossil remains from sediment cores taken from the Santa Barbara Basin. h ey
used two species of foraminifera: Globigerina bulloides, a surface dweller,
and Neogloboquadrina pachyderma, a species that lives at about 60 meters'
(195 feet) depth, where ocean temperatures become much cooler. h eir results
show that coastal waters were unusually warm (by 2-3°C, or 3.5-5.5°F) from
11,000 to 10,300 years ago. At er that time, during the earliest Holocene,
temperatures began to drop, cooling by 4-5°C (7-9°F), and remained low for
the next 1,500 years. Temperatures then increased again between 8,200 and
6,700 years ago, and they fell once more between 6,700 and 5,200 years ago.
h ese millennial-scale climate cycles during the Holocene were initially
identii ed about a decade ago in climate records from Greenland ice cores and
North Atlantic sediment cores. Since then, researchers have found evidence
for them in pollen records showing vegetation change throughout North
America as well as marine records from the Pacii c Ocean. We will return to
these broad cycles of climate in the next few chapters and will discuss their
possible causes in chapter 11.
h e transition from the peak of the last ice age to the Holocene encom-
passed some of the most rapid and monumental climate shit s in the geologic
record. Global cooling at the peak of the last ice age is important because
it represents a period when the climate was quite dif erent from the warm
conditions we experience today and are likely to experience in the future.
h e evidence shows that the West was signii cantly wetter during this cooler
period, resulting in the formation of the enormous Great Basin lakes, which
were ten times larger than they are today. h ese lakes have since largely dried
up, and they are predicted to dry even more as the climate continues to warm.
As these lakes gradually desiccate into salt l ats, they serve as a warning of how
rapidly water can vanish in a region that is highly sensitive to climate change.
Compared to the monumental environmental and climatic upheaval of the
previous ice age, the Holocene epoch was a more tranquil period. h ere were
no wild expansions and contractions of great lakes; no large, abrupt shit s in
temperature. Even so, the climate l uctuations and extremes of the past 11,000
years have been large enough to dramatically alter the landscape, disrupt human
societies, and, in some cases, lead to mass migration and societal collapse. As we
shall explore in the next chapter, the most extreme of these l uctuations was one
of the longest and most severe droughts of the Holocene in the West.
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