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CHAPTER 12 • Last Glacial Maximum 215

lent atmosphere that carried dust farther south than
today.
Almost everywhere we look, evidence shows that
more debris was blowing across Earth’s surface in the
glacial world. One way of testing climate model simula-
tions of the last glacial maximum is to examine the
distribution of various kinds of debris carried by winds,
ranging from desert sands to windblown silts (loess) and
fine (clay-sized) dust. Because climate models can simu-
late the strength and direction of winds from the
surface up to jet stream altitudes, the potential exists to
Loess deposits compare model simulations with the observed patterns
of windblown glacial debris.
Unfortunately, even though the current generation
FIGURE 12-4 Glacial maximum loess Ice sheets and
mountain glaciers eroded large amounts of debris of all sizes of climate models does a fairly good job of simulating
and carried it to their margins. Winds picked up silt-sized loess the large-scale circulation of the atmosphere, the mod-
and deposited it downwind of these sources. (Adapted from K. els do not do as good a job at the smaller scales needed
Pye, “Loess,” Progress in Physical Geography 8 [1984]: 176–217.) to simulate dust transport. The models are less success-
ful at simulating the processes that actually lift and
transport silt and dust from Earth’s surface, such as local
wind gusts along frontal systems or small-scale eddies of
than nearby North America. Glacial ice also contains wind.
–
+
more Na and Cl ions, an indication that far more salt
was lifted from stormy glacial sea surfaces and deposited
in the ice then than today.
Dust transport was also greater at lower latitudes
during the last glacial maximum. Today the North North
tropic
African and Arabian deserts and their semiarid margins
produce some of the largest dust storms on Earth. By
comparison, sediment cores from the Indian Ocean east
of the Arabian Peninsula show that dust accumulated Equator
five times faster during the last glacial maximum and
during several previous glaciations than it does today. South tropic
Cores from the equatorial Atlantic Ocean reveal that
dust was also deposited in that region at higher rates
during glaciations.
The extremely arid cores of the deserts were also A Sand dunes active today
affected (Figure 12–5). Regions of Arabia and North North
Africa identified as deserts on modern maps have actu- tropic
ally varied in moisture level through time: moving sand
dunes and loose soil are prevalent during extremely arid
intervals, but the dunes are stabilized by sparse desert Equator
vegetation during monsoonal intervals that are moister
(Chapter 8). In these areas and in Australia as well, South tropic
moving sand dunes were much more extensive during
the last glaciation than they are today because the winds
were stronger and the climate was drier.
Even the South Pole was dustier. Glacial-age layers
of ice cores from Antarctica contain more than ten B Sand dunes active at glacial maximum
times as much dust as modern interglacial layers. FIGURE 12-5 Glacial maximum sand dunes (A) Moving
Geochemical fingerprinting of likely source areas sand dunes occur today in Africa, Arabia, and Australia.
suggests that this dust came from the southernmost (B) At the last glacial maximum, drier climates and stronger
tip of South America (Patagonia). The increased flux winds created more extensive sand dunes. (Adapted from M.
of dust probably resulted both from greater pro- Sarnthein, “Sand Deserts During Glacial Maximum and Climatic
duction of debris at the sources and from a more turbu- Optimum,” Nature 272 [1978]: 43–46.)