FIGURE 8.1 Locations of Pacific and Atlantic Ocean cores discussed in text.

FIGURE 8.2 Pleistocene-Holocene eolian flux to the Pacific Ocean.

The most flux data exist for the North Pacific where essentially all of the eolian dust deposited comes from central and western China and Mongolia. That material is transported to the east by the westerlies and the westerly jet stream, then drifts south towards the equator and dominates eolian deposition all the way south to the Intertropical Convergence Zone (Merrill et al., 1989). Flux rates decline all along this transport path (Figure 8.2).

Rea and Leinen (1988) reported on the late Glacial to Holocene eolian records of a suite of six cores along a latitudinal profile extending from 28.4°N to 46.6°N between 155° and 160°E. Data from those cores (Figure 8.3) show distinct latitudinal variations in dust flux with a present-day maximum of about 1000 mg/cm2/kyr at 38° to 40°N and flux values falling off to the north and south. The latitudinal position of the flux maxima has remained unchanged through the last 30,000 years, although the amount has varied (Rea and Leinen, 1988). Farther east, at the same latitude of 37 to 40°N and between 174 and 179°E, the flux of dust in uppermost samples (i.e., Pleistocene, not Holocene) of DSDP and piston cores is approximately 250 mg/cm2/kyr, a significant decline in about 1500 km of transport distance.

To the south of the main region of the westerlies, the eolian fluxes in the central North Pacific decline to less than 100 mg/cm2/kyr at about 30 to 35°N, depending on longitude. Flux values from three equatorial cores whose late Glacial and Holocene records were studied in detail, all from about 1°N and spaced between 109 and 179°W, remain quite constant at 10 to 20 mg/cm2/kyr over the past 30 kyr (Figure 8.4). The Holocene flux value from DSDP Core 503B at about 4°N, 96°W, somewhat closer to the presumed South American source area, is slightly greater (Rea et al., 1986).

We have determined the flux of eolian dust to the South Pacific for five of the DSDP Leg 92 drill sites which were spaced along 19°S from 130 to 117°W (Figure 8.1; Bloomstine and Rea, 1986). The flux value of the uppermost sample from each of these cores averaged 1 mg/cm2/kyr and was never greater than 1.8 mg/cm2/kyr. Eolian fluxes to the South Pacific are very low and have been so at least since the Oligocene (Rea and Bloomstine, 1986). Results from the southern Indian Ocean indicate similarly low fluxes for most of the Cenozoic (Hovan and Rea, 1991).

The Pacific data are adequate to construct a map of the flux of eolian dust to the ocean (Figure 8.2). The data mapped (Table 8.1) include both Holocene and whole-Pleistocene values so the map does not represent a true (i.e., restricted) time slice. Nevertheless the primary flux patterns are clear. High eolian accumulation rates near Asia decrease to the east along a latitude band approximately 35 and 45°N from over 1000 to less than 250 mg/cm2/kyr in the central North Pacific. Isopleths of eolian flux trend east-west, matching the pattern of present-day transport (Merrill et al., 1989) and the pattern of mineralogy of sea-floor surface sediments (Leinen et al., 1986). There is an order of magnitude decline in dust input along about 30° N from the high values to the north to values of a few tens of mg/cm2/kyr in the northern subtropics. Another order of magnitude decline occurs at the Intertropical Convergence Zone, where the rainfall associated with the equatorial low serves as an effective barrier to the interhemispherical transport of dust.

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