Dust cycle: An emerging core theme in Earth system science

The dust cycle is an integral part of the Earth system. Each year, an estimated 2000 Mt dust is emitted into the atmosphere, 75% of which is deposited to the land and 25% to the ocean. The emitted and deposited dust participates in a range physical, chemical and bio-geological processes that interact with the cycles of energy, carbon and water. Dust profoundly affects the energy balance of the Earth system, carries organic material, contributes directly to the carbon cycle and carries iron which is vital to ocean productivity and the ocean-atmosphere CO sub(2) exchange. A deciphering of dust sources, transport and deposition, requires an understanding of the geological controls and climate states - past, present and future. While our knowledge of the dust cycle, its impacts and interactions with the other global-scale bio-geochemical cycles has greatly advanced in the last 30 years, large uncertainties and knowledge gaps still exist. In this review paper, we attempt to provide a benchmark of our present understanding, identify the needs and emphasise the importance of placing the dust issue in the Earth system framework. Our review focuses on (i) the concept of the dust cycle in the context of global biogeochemical cycles; (ii) dust as a climate indicator; (iii) dust modelling; (iv) dust monitoring; and (v) dust parameters. The adoption of a quantitative and global perspective of the dust cycle, underpinned by a deeper understanding of its physical controls, will lead to the reduction of the large uncertainties which presently exist in Earth system models.