The impacts of Lake-Dust on Global Dust Cycle and Direct Radiative Effects

Ephemeral lakes, also called playas, have been identified as dust hot spots. Although their total surface is a small fraction of arid regions, their contribution to global emission may be significant. The surface of ephemeral lakes is generally composed of alluvium, which differs from the mineralogical composition of their surroundings. This contrast of soil composition will transfer to dust interactions with Earth’s climate systems, in particular radiation. This study aims at investigating, for the first time, the contribution of ephemeral lakes to global dust cycle, and their impacts on optical properties and radiative effects.

In this study, we categorized dust sources into two groups: ephemeral lakes (referred to as lake sources) and regular dust sources (referred to as surrounding sources). The surrounding sources are identified as topographic lows with bare ground surface, as suggested in Ginoux et al. (2001). Dust from surrounding sources is assumed to contain 0.9% hematite by volume, as indicated in our recent study Song et al. (2024). Lake sources are identified using the ephemeral water data from MODIS/Terra Level 2G Daily Surface Reflectance State data product (MOD9). We varied the hematite content of lake dust from 0.1% to 4.0% to investigate how dust scattering properties and radiative effects depend on the contrasting soil composition between lake and surrounding sources. We use GFDL-AM4.0 model to simulate the dust cycle and the direct radiative effects of dust from surrounding and lake sources, respectively. We found that lake dust contributes approximately 15% to global dust emission, with around 10% in the Northern Hemisphere (NH) and more than 55% in the Southern Hemisphere (SH), highlighting ephemeral lakes as the primary dust sources in the SH. Global dust absorption is highly sensitive to lake dust hematite content, with global mean dust single scattering albedo (SSA) varying from 0.94 to 0.91. The radiative effects of lake dust transition from cooling to warming over regions including Northern Africa, Middle East Asia, and Australia with increasing hematite content.

Overall, ephemeral lakes play a dominant role over the SH in the dust cycle and its impacts on radiation. In the NH, its contribution is smaller but still significant, particularly on regional and local scale.