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traveled dust are also important paleoclimate indicators because they yield information about synoptic-scale circulation. Records in deep-sea sediment cores, ice cores, and soils indicate that the Americas have been both a source and a sink for far-traveled, fine-grained dust.

Darwin (1846) was one of the first investigators to observe airborne dust over the Atlantic Ocean enroute to the Americas. A century later, numerous researchers have confirmed that African dust travels to the Americas via the northeasterly trade winds (Fig. 21). Delany et al. (1967), Prospero et al. (1970, 1981), and Prospero and Nees (1977, 1986) demonstrated, through analysis of satellite imagery and dust trap collections, that African dust falls on Florida, Barbados, and northern South America. By the time it reaches the western Atlantic Ocean, airborne dust from Africa is composed mostly of particles less than 20 ^m in diameter, and about half of this is clay-sized material less than 2 ^m in diameter (Prospero et al., 1970). The most important mineral in the silt-sized fraction is quartz, and mica dominates the clay-sized fraction (Delany et al., 1967; Glaccum and Prospero, 1980). The modern flux of dust from Africa is, to a great extent, a function of the degree of aridity in the southern Sahara and Sahel (Prospero

FIGURE 18 Map showing the distribution of eolian sand and loess and paleowinds inferred from eolian sand data in Alaska and northwestern Canada. E, Epiguruk (see Fig. 20); UT, upper Tanana River (see Fig. 20); MT, middle Tanana River (see Fig. 20); LT, lower Tanana River (see Fig. 20); D, Dawson, Yukon Territory, Canada (see Fig. 19). Eolian sand and paleowinds data are from Lea and Waythomas (1990); loess distribution is redrawn from Pewe (1975).

FIGURE 18 Map showing the distribution of eolian sand and loess and paleowinds inferred from eolian sand data in Alaska and northwestern Canada. E, Epiguruk (see Fig. 20); UT, upper Tanana River (see Fig. 20); MT, middle Tanana River (see Fig. 20); LT, lower Tanana River (see Fig. 20); D, Dawson, Yukon Territory, Canada (see Fig. 19). Eolian sand and paleowinds data are from Lea and Waythomas (1990); loess distribution is redrawn from Pewe (1975).

SEWARD PENINSULA, ALASKA

EVA CREEK, FAIRBANKS, ALASKA

FOX, FAIRBANKS, ALASKA

DAWSON, YUKON, CANADA

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