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Deforestation Strengthens Dust Transport from North Africa to the Amazon

Presentation Date
Monday, December 7, 2020 at 5:38pm



Atmospheric mineral dust originating from Africa contains micronutrients that fertilize both surface marine ecosystem in Atlantic Ocean and tropical forest in Amazonia. However, the mechanism of land use and land cover change (LULCC) impacts on such nutrient transport pathway remain poorly understood. In this presentation, we use the Community Earth System Model (CESM) to investigate how large-scale deforestation affects the dust transport and deposition in the tropics. We find that surface biophysical changes (i.e., albedo increase, evapotranspiration and surface roughness decline) that accompany deforestation produce a warmer, drier and windier surface environment, which enhances the long-range dust transport from North Africa to the Amazon. Tropics-wide deforestation weakens Hadley circulation (HC) through reducing the surface latent heating that weakens the vertical velocity in deep tropics. The weakened upward branch of HC tends to force the tropical air poleward and this shift of more stable air tends to increase subtropical static stability. Such atmospheric perturbation is related to the poleward expansion of HC that leads to the increase of local surface air pressure in North Africa. Local northeasterly winds increase accordingly and make the dust in North Africa more easily to be transported across the tropical North Atlantic Ocean. We estimate that the annual atmospheric phosphorus deposition from dust thereby increases by about 26±25% in the Amazon. Our results exemplify how LULCC can modify the tropical nutrient transport, the change of which may have important implications for the long-term changes in productivity and biodiversity of tropical ecosystems.

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