Apr 26, 2012
Kalahari Desert could dust up Southern Ocean
Take a deep breath. If you live in the northern hemisphere then you will have inhaled a fair amount of dust. If you live in the southern hemisphere that breath was relatively dust free. However, new research indicates that the southern hemisphere is set to become dustier, as the South-African Kalahari Desert starts to erode. Ultimately, this additional airborne sand may breathe new life into ocean ecosystems.
Over 90% of the world's airborne dust originates from northern hemisphere sources, such as the Bodélé Depression in northern Chad and the Sahara Desert in North Africa. Little of this dust makes it over the equator, and the ocean-dominated southern hemisphere has fewer dust sources of its own, leaving its air relatively dust free. However, the southern hemisphere has some dust sources waiting in the wings.
The Kalahari Desert, in Botswana, Namibia and South Africa, is one such source. Today the dunes are covered in vegetation, which bind its dusty soil to the ground, but gradually the desert is changing. "Overgrazing and aridification are leading to an increase in dust emissions," said Paolo D'Odorico, from the University of Virginia in the US.
How much dust could the Kalahari release and what impact would it have? To answer this question, D'Odorico and colleagues collected soil samples from the Kalahari and analysed how they might behave if the dunes were bare of vegetation. They then compared their Kalahari dust with samples taken from contemporary southern-African dust sources – the Etosha and Makgadikgadi pans, in Namibia and Botswana, respectively.
Each sample was placed in a custom made "dust generator" – a rotating tube with a gentle flow of air wafting through. Potential dust was carried by the breeze into a dust sensor, which measured the size distribution of the particles.
The team's results, published in Environmental Research Letters, show that if the Kalahari loses its vegetation it is capable of producing significant volumes of dust, comparable to those currently coming from the Etosha and Makgadikgadi pans. "We found that the inter-dune areas [valleys between dune crests] are richer in fine particles and can be expected to become the major contributors to dust emissions in the region," D'Odorico told environmentalresearchweb.
However, unlike dust bowls, deserts tend to provide a limited source of dust. The researchers estimate that the Kalahari would be a relatively short-lived dust generator, running out of dust after just one to two decades. Nonetheless, this dust would make its mark.
"Our trajectory analysis shows that the current wind regime is sufficient to transport dust to the Southern Ocean," said D'Odorico. Once there, the soluble iron content of the dust would be likely to trigger a burst in ocean productivity, feeding new algal blooms and supporting entire ocean ecosystems.
Meanwhile, a similar scenario is likely to be played out in other southern hemisphere locations. Already there is evidence that deforestation and overgrazing in Patagonia, South America, and droughts and land-use change in Australia's deserts are adding to the southern hemisphere's dust load. The future looks hazy down south.
D'Odorico and colleagues reported their findings in Environmental Research Letters (ERL).
About the author
Kate Ravilious is a contributing editor to environmentalresearchweb.