By: Brendan Alvis
Summary: The Saharan desert is the largest source of mineral dust on Earth. “The arid regions of North Africa are estimated to emit about 800 Tg yr−1 of soil dust each year, 70% of the global total and six times more than the next largest source, Asia (Huneeus et al. 2011).” This is equivalent to 8 x 10^11 kg/year of dust. The destination of this dust can be discerned based on air and ocean circulation trends in the Atlantic. Because of the area of high pressure sitting in the north central Atlantic, the prevailing winds, known more commonly as trade winds, move from the west coast of Africa straight across to the Caribbean. As a result, the tropical Atlantic, Amazon, and Caribbean can be thought of as the primary repositories of Saharan dust.
What are some of the effects of this massive amount of sediment being transported? Firstly, the mineral matter can be an excellent source of nutrients for phytoplankton and other aquatic organisms as well as a soil fertilizer in the Americas. Surges in dust transportation have been associated with algal blooms across the Atlantic. It also has been found that Saharan dust can have negative impacts on coral reefs, although the exact mechanism is debated. Other relevant impacts include negative effects on human health/air quality as well as altering marine biogeochemical processes. Finally, the dust can have atmospheric impacts. High dust concentration and the associated meteorologic conditions associated with Saharan dust transportation can moderate tropical cyclones and hurricanes by lowering the ocean temperature. “These changes, in turn, could be linked to the suggested negative correlation between Atlantic dustiness and hurricane activity. Cloud microphysics could also be affected by African dust, which can serve as both condensation (Twohy et al. 2009) and freezing nuclei (Cziczo et al. 2013; Heymsfield et al. 2009).” The levels of particulate in the atmosphere can impact levels of albedo, or reflectivity and alter levels of radiation and subsequent temperature of the air. It seems that something as simple as dust can have large impacts far from their origin.
Why we should care? The Sahara produces massive amounts of dust and mineral matter that is transported and deposited by global circulation. This can impact: soil fertilization, marine biogeochemical processes, air quality, and climate and weather worldwide.
Example News Article:
This article discusses a Saharan dust plume that was headed towards Florida and its moderating effects on the atmospheric conditions/ tropical storm development in the area. I found it particularly interesting that they could estimate the exact location of the source of the majority of the dust. This ended up being the dried up lake bed of Lake Chad, now known as the Bodélé Depression in the southern Sahara. Also, it was interesting that the layer of dust-laden air spread from 5,000 feet all the way up to 20,000 feet.
Science in Action.
Dr. Joseph M. Prospero is Professor Emeritus at University of Miami-Rosenstiel School of Marine and Atmospheric Science.
Dr. Prospero's research focuses on the chemistry and chemical processes associated with the transport of aerosols into the ocean. Specifically, he was a large contributor to the discovery of wind-delivered iron as a limiting factor of marine ecosystems. He studies the source of dust, the properties of dust, and the effects of climate on dust using modeling. Interestingly, he is now studying the long range transport of microorganisms such as bacteria and fungi by the trade winds.