Introduction

The atmosphere and the oceans are joint partners in transporting energy and moisture around the globe. Atmospheric circulation not only transports energy and moisture but also particles of dust. Wind transports dust from the continents to the deep ocean basins, where it may play a significant role in supplying biologically available iron to marine phytoplankton (Martin, 1990). At the present day, biological productivity and biomass are limited by iron deficiency in some areas of the world's oceans (e.g. the Southern Ocean). Increased marine productivity may have occurred during past glacial events due to significantly enhanced continental aridity and aeolian transport. Dust concentrations in ice cores from Greenland and Antarctica show that dust fluxes during glacial periods were approximately five to 20 times higher than during interglacial periods (Thompson & Mosley-Thompson, 1981; Petit et al., 1981). Such changes in aeolian transport can in turn exert a major climate feedback, via drawdown of carbon and significant reduction of atmospheric CO2 levels. Major present-day sources of modern dust can readily be identified from remotely sensed ocean-haze data (see Fig. 3.3, Chapter 3). They include north and northwest Africa, south-east Asia, the Indian subcontinent, Arabia, central America and eastern Europe (especially around the Black Sea).

Records of past variations in dust supply and transport exist not only in ice cores but in marine and lake sediments and in terrestrial sequences of loess. Such records can provide a natural archive of past changes in (a) wind patterns and intensities, and (b) dust source areas. As summarized by Rea (1994), three uniformitarian principles are normally applied to interpret the geological record of aeolian dust supply to the oceans.