GEOLOGIC RECORDS OF DUST IN THE QUATERNARY: A REVIEW AND EVALUATION

Geologic records of dust, including information about their composition, sources and deposition rates, are crucial for understanding the role of dust in the overall planetary radiation balance, fertilization of organisms (e.g., primary producers such as phytoplankton) in the world’s oceans, and nutrient additions to the terrestrial biosphere and soils. Dust is also one of the most direct pieces of evidence for past atmospheric circulation and thus is important for paleoclimatic reconstructions. Both glacial and non-glacial processes produce dust-sized (fine silt and clay) particles that can be transported by the wind. Records of dust occur in a number of geologic archives: (1) loess deposits; (2) lake sediments; (3) soils; (4) deep-ocean basins; and (5) polar ice sheets and smaller glaciers. These depositional records have several characteristics that make them highly suitable for understanding the dynamics of dust entrainment, transport, and deposition. First, they are often distributed over wide geographic areas, which permits reconstruction of spatial variation of dust flux. Second, a number of dating methods can be applied to sediment archives, which allows identification of specific periods of greater or lesser dust flux. Third, aeolian sediment particle size and composition can be determined so that dust source areas can be ascertained and dust transport pathways can be reconstructed. Over much of the Earth's surface, these records show that dust deposition rates were greater during glacial periods compared to interglacial periods. A dustier Earth during glacial periods is likely due to increased source areas, greater aridity, less vegetation, lower soil moisture, possibly stronger winds, a decreased intensity of the hydrologic cycle, and greater production of dust-sized particles from expanded ice sheets and glaciers.