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Saharan Dust: The Good and The Bad

Each year, beginning in the late spring and continuing through early fall, a haze seems to settle around St. Croix. While this haze can give the appearance of a light fog off in the distance, it is actually dust in the atmosphere originating from Africa. This phenomenon is called the Saharan Air Layer, or, as it is more commonly known here on the island, Sahara dust.

According to the Hurricane Research Division of National Oceanic and Atmospheric Administration (NOAA), the Saharan Air Layer forms over Africa and moves out into the tropical Atlantic Ocean about every 3-5 days. Generally located between 5,000 and 15,000 feet above the earth’s surface, the Saharan Air Layer is transported westward from Africa by bursts of strong winds in the central and western Atlantic. As crazy as it seems, not only does the Saharan dust effect the Caribbean, but has been found to influence levels of precipitation as far away as California!

Saharan Dust: The Good and The Bad

When the Saharan dust season is in full swing here on St. Croix, there are a few unpleasant side effects that blow in with the dry, dusty air. First, the dust gets everywhere. No matter how much you try to keep your house, car or office cleaned, a fine layer of dust seems to be permanently settled on every surface. Second, the dust in the atmosphere raises the heat index; so, in addition to the warmer temperatures of summer, the air also feels hotter. Third, the dust can wreak havoc on those with allergies or respiratory conditions, whether human or animal. So, stock up on your allergy medications, eye drops, and nose sprays.

Saharan dust hangs in the air over Christiansted Harbor

As for it’s impact on the Caribbean, Saharan dust is rich in minerals, like iron – making it essentially an airborne fertilizer for marine life as well as tropical rainforests. Unfortunately, this same ‘fertilizer’ encourages the growth of algae blooms and toxic algae blooms (known as ‘red tides’) in the sea which have been responsible for the deaths of huge numbers of fish and other marine life in the past. Researchers have also linked Saharan dust to coral disease. Coral reefs in the Caribbean have been in a state of decline since the 1970s, and several other marine species suffered mass mortalities in 1983. Coincidentally, the Saharan Air Layer has increased dramatically since the 1970s, with peak dust years occurring in 1973, 1983, and 1987. According to Gene Shinn, Senior Geologist at the U.S. Geological Survey Center for Coastal Geology: ‘Our hypothesis is that much of the coral reef decline in the Caribbean is a result of pathogens transported in dust from North Africa.’

Now for the good news… according to NOAA, the Saharan Air Layer can weaken tropical cyclones by creating downdrafts (sinking air) around the storm, which may result in the weakening of tropical systems. The strong winds of the Saharan Air Layer can also substantially increase the vertical wind shear in and around tropical systems, making the conditions hostile for tropical storm development. Translation: the Saharan Air Layer helps to lessen the intensity of tropical storms and hurricanes! Having been through the devastation of  Hurricanes Irma and Maria, I would say this is definitely a good thing.

While it can be a nuisance, Saharan dust is a reality of island life. While there are issues that arise from the dust, remember that the Saharan Air Layer also brings benefits. This mineral laden dust provides nutrients for the health of our rainforests and for sustaining life over much of the Northern Atlantic Ocean, as well as being key factor in suppressing potentially dangerous hurricanes. Just remember, EVERY cloud has a silver lining, even a dust cloud.

– Jennie Ogden, Editor

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