Massive dust emitted from the Sahara Desert is carried by trade winds across the tropical Atlantic Ocean, reaching the Amazon rainforest, Caribbean Sea, and southeastern United States and affecting the environment in many ways. Airborne dust degrades air quality and interacts with radiation and clouds. Dust falling to land and ocean adds essential nutrients that could increase the productivity of terrestrial and aquatic ecosystems and modulate the biogeochemical cycles. Furthermore the climate change resulting from the dust influences on radiation, clouds, and biogeochemical cycles will feed back on the production of dust in the Sahara and its subsequent transport and deposition. Long-term observations of the three-dimensional (3D) structure of dust are needed to advance the understanding of dust long-range transport and its complex roles in the climate system. In this talk, I will present results of using an 8-year (2007-2014) record of CALIPSO lidar measurements of aerosol 3D distributions to characterize the temporal and spatial variability of trans-Atlantic dust transport and deposition and assess its implications for fertilizing Amazon rainforest and degrading air quality in the Caribbean Basin. In this study, dust is distinguished from other types of aerosol by using CALIPSO measured particulate depolarization ratio. The mass fluxes of dust transport and deposition and dust lifetime are then estimated. On a basis of the 8-year average, approximately 180 Tg (1 Tg = million tons) of dust leaves the coast of North Africa and is transported across the Atlantic Ocean. 34 Tg dust is imported to the lowest 1 km atmospheric layer of the Caribbean Basin, which significantly degrades air quality in the region. During the cross-ocean transport with an estimated lifetime of 9 days, about 102, 20, and 28 Tg of dust is deposited into the tropical Atlantic Ocean, Caribbean Sea, and Amazon Basin, respectively. The dust deposition into the Amazon provides the amount of phosphorus that replenishes the leak of this plant-essential nutrient from the basin by rains and flooding, suggesting an important role of Saharan dust in maintaining the productivity of Amazon rainforest on decadal or century timescale. The CALIPSO-based estimates are compared or evaluated with those derived from measurements of passive sensors (e.g., MODIS, MISR, AIRS, and IASI), GOCART simulation, and MERRA2 reanalysis.
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