Loess or reworked loess

Paleosol, peat, or woody zone


FIGURE 21 Modern summer and winter circulation patterns over a portion of the Atlantic Ocean, the location of modern Saharan dust plumes, and the ratio of last glacial maximum (LGM) to modern dust fluxes as recorded in deep-sea cores between Africa and South America. (Redrawn from Ruddiman 1997.)

and Nees, 1977), but measurable dust has been collected in Florida and Barbados most years since collections began in the 1960s (Prospero, 1981).

It has been known for some time that deep-sea sediments in the Atlantic Ocean that date to the LGM are enriched in quartz relative to Holocene sediments (Bowles, 1975; Kolla et al., 1979). Quartz enrichment in the North Atlantic is due to ice rafting, but in the equatorial Atlantic it is interpreted to be the result of westward eolian transport of quartz-rich particles from Africa via the trade winds. Deep-sea sediment records and soils indicate that African dust transport to the Atlantic Ocean and the Americas have been an important process for hundreds of thousands of years, and show distinctive maxima (Fig. 22). At site 663A in the Atlantic Ocean, maximum fluxes of African dust to the Atlantic Ocean generally occur during glacial or stadial periods, whereas peak interglacial periods have low dust fluxes (deMenocal et al., 1993; Ruddiman, 1997). Studies of soils on high-purity carbonate reef terraces and eolian-ites on Barbados, the Bahamas, and the Florida Keys show that they are unlikely to have formed as residual products by carbonate dissolution (Muhs et al., 1987, 1990). Lesser Antilles island arc volcanic ash deposition on these islands has been an important process in the Quaternary period (Carey and Sigurdsson, 1980). It is possible that soils have developed primarily from this source. However, geochemical analyses show that African dust is a much more likely parent material and has been so for the last several glacial-interglacial cyles (Fig. 22).

Some of the highest resolution paleoclimate records of the Americas are ice cores from glaciers in the high Andes of South America. Dust flux is one of the records available from these cores, and there are differences over both time and space. The Huascaran, Peru, ice core shows a dust flux during the LGM that is about 200 times greater than most Holocene values (Thompson et

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