The Harmattan: The Winds of Life and Death, Part I
On Thursday January 17th, 2013, the residents of Siesta Key, Florida woke to an unpleasant sight. Dead fish in the thousands were washing up on the beach, vomited from the sea on the incoming tide. The fish were killed; victims of a red tide. Red tides are the colloquial name given to a phenomenon called algal blooms, rapid, explosive growths of toxic algae which float in slimy mats across large expanses of the ocean. Algal blooms kill fish and other marine wildlife by clogging their gills with slimy muck and asphyxiating them, by sucking all of the available oxygen from the water column, and by releasing toxic chemicals. They’re not much better for humans – causing respiratory problems if the water is swam in, and even death if people consume contaminated shellfish. Red tides are a recurrent nightmare for ocean-front communities throughout the Caribbean and up and down the East Coast. They cause severe economic damage by shutting down tourism and fisheries for months at a time.
Most algae grow at low densities because they cannot acquire the necessary nutrients to grow faster. They live a tenuous existence, constrained by the emptiness of the ocean. But like an oxygen starved fire, they need only a spark to burst into uncontrollable life. For algae, that spark is iron. The growth of algae is constrained by a lack of iron. Iron is rare in the open ocean – most biologically available iron comes from dust and soil blown into the sea. That happens regularly, but its not usually enough for algae to take advantage of, so they’re said to be iron-limited. But occasionally, a massive influx of iron – like opening the door on a backdraft – causes an explosive growth of algae which leads to a bloom. The source of those periodic iron influxes is an unlikely one. The spark which causes algal blooms in North American comes from many thousands of miles away, deep in the Sahara Desert. It is one of the greatest shows of primal force and power found anywhere on Earth, capable of influencing weather on a global scale. It is the harmattan.
Lawrence Durrell, in his novels The Alexandria Quartet, provides a vivid description of the harmattan:
Before sunrise the skies of the desert turned brown as buckram, and then slowly darkened, swelling like a bruise and at least releasing the outlines of cloud, giant octaves of ochre which massed up from the Delta like the drift of ashes under a volcano. The city has shuttered itself tightly, as if against a gale. A few gusts of air and a thin sour rain are the forerunners of the darkness which blots out the light of the sky. And now unseen in the darkness of shuttered rooms the sand is invading everything, appearing as if by magic in clothes long locked away, books, pictures and teaspoons. In the locks of doors, beneath fingernails. The harsh sobbing air dries the membranes of throats and noses, and makes eyes raw with the configurations of conjunctivitis. Clouds of dried blood walk the streets like prophecies; the sand is settling into the sea like powder into the curls of a stale wig.
Michael Ondaatje, in The English Patient, adds another:
Travelling alone the ground like a flood. Blasting off paint, throwing down telephone poles, transporting stones and statue heads. The harmattan blows across the Sahara filled with red dust, dust as fire, as flour, entering and coagulating in the locks of rifles. Mariners called this red wind the “sea of darkness.” Red sand fogs out of the Sahara were deposited as far north as Cornwall and Devon, producing showers of mud so great this was also mistaken for blood.
In Arabic it is called the kamsin, meaning 50, because it blows for 50 days. The Tuareg, blue-veiled nomads of the Sahara are the ones who call it harmattan, poetically The Hot Wind of the Desert, but more literally, just “evil thing.” In the more staid realm of meteorology, it is a West African Trade Wind, originating in the Sahara near Lake Chad. But that’s hardly exciting.
The harmattan is the troubled offspring of two major wind systems which clash over North Africa: moist tropical winds blowing up from the equator, and cooler, subtropical winds coming down from the north. In winter these two fronts collide at the southern edge of the Sahara, the Sahel, and the harmattan is born – a powerful, spinning “extratropical cyclone” that blows north and west across the desert.
To say it stirs up sandstorms is an understatement. A member of the French Foreign Legion once wrote that the harmattan travels, “as a mist or fog of dust as fine as flour, filling the eyes, the lungs, the pores of the skin and nose.” It is a hot, dry wind which blows incessantly for months. Humidity can drop as low as 10%; all of the moisture is sucked from the air, causing spontaneous nose bleeds. Visibility is minimal. The sand creeps everywhere, and cities shut down – their people hidden behind windows and walls as the mercury climbs to 50 degrees C. In 1927, the harmattan derailed a train in Algeria. In 1999, it decimated a grove of date palms at an oasis in Mali. Without the life-giving sustenance of the trees, the community was abandoned within a week.
But the harmattan is too powerful to be contained to just one continent. The violent convective winds that swirl through the Sahara jettison thousands of kilograms of dust and sand kilometres into the atmosphere, where they are grabbed by high altitude winds and whisked out to sea.
Of course, and as is always the case, Darwin noticed it first. On January 16th, 1833, the HMS Beagle was travelling passed Santiago, the largest island of Cape Verde (an island republic a short hope from Africa’s west coast). In his journals, Darwin wrote that, “the atmosphere was so hazy that the visible atmosphere was only mile distant.” Owing to the direction of the wind, he surmised that, “the dust probably came from the coast of Africa”. The novelty of the ocean dust wore off quickly, as the constant whirl of sand grains infiltrated every nook and cranny of the Beagle, and damaged the delicate compasses and sextants on which the sailors relied.
Caught in tropospheric air currents, dust from the harmattan takes a week to cross the Atlantic, before depositing as a silty shower in North and South America. One estimate says that as much as 20% of the soil on the eastern seaboard has its origins in North Africa. The iron-rich dust of the desert bleeds into the ocean half a world away, where it triggers toxic algal blooms. Along with dust, the winds carry microbes and fungal spores across the ocean, which are linked to the decline of coral reefs in the Caribbean. Humans can be harmed more directly too – the winds carry fungal meningitis spores around the world. In North Africa, outbreaks of meningitis regularly follow in the wake of the harmattan.
But the harmattan doesn’t just bring death; it also brings life. Part II tomorrow.
Repost of an article originally written for other-nations.com
Feature photo credit: Aka Teraka, akateraka.wordpress.com
Garrison et al. 2003. African and Asian Dust: From Desert Soils to Coral Reefs. Bioscience 53.
Herald-Tribune. “Red tide, fish kill reported at Sarasota beaches”, January 17th 2013.
Stoorvogel JJ, N Van Breemen and BH Jassen. 1997. The nutrient input by Harmattan dust to a forest ecosystem in Cote d’Ivoire, Africa. Biogeochemistry 37: 145-157.
Prospero, JM. 1996. Saharan Dust Transport Over the North Atlantic Ocean and Mediterranean: An Overview, in The Impact of Desert Dust Across the Mediterranean. Editors: S Guerzoni and R Chester. Kluwer Academic Publishers: Nowell, USA.
Ondaatje, M. 1993. The English Patient. Vintage Canada: Toronto, Canada.
de Villiers M, and S Hirtle. 2003. Sahara: A Natural History. McClelland and Stewart Ltd: Toronto, Canada.