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  • [♩ INTRO ]

  • When you eat a tomato from Florida, chances are it was grown in African soil.

  • But not because someone shipped the dirt over there or anything.

  • Every year, tons of dust from the Sahara desert is kicked up by dust storms, blasted high

  • into the sky, and whisked across the Atlantic Ocean on wind currents.

  • It takes about a week.

  • Then, it's hello, Florida.

  • In fact, our oceans and continents are all linked into this weird, global dust ecosystem.

  • Whether it's going from Australia to New Zealand or from Asia to Oregon, the current

  • estimate, worldwide, is that 3 billion tons of dust move through the atmosphere every

  • year.

  • It comes with some powerful, and surprising, global effects, not all of which are good.

  • But one way or another, this dust is definitely changing our world.

  • Scientists can track how the dust moves using satellite images or by analyzing soil samples.

  • The dust in certain regions tends to contain specific kinds or amounts of elements, and

  • they act kind of like a fingerprint.

  • So by measuring where those fingerprints turn up, the researchers can see how the dust has

  • migrated and what its effects are.

  • A lot of those effects involve ecology.

  • Like for starters, dust builds soil.

  • Lots of soil.

  • Scientists estimate that more than 30% of the soil in Barbados comes from Africa.

  • And the stuff in the Bahamas and the Florida Keys?

  • Mostly African imports.

  • Besides being weird to think about, the dust is also really important.

  • In fact, without African dust, the vegetation on some Caribbean islands wouldn't be nearly

  • so lush.

  • See, those islands, along with parts of Florida, are mostly built of crusty coral.

  • When that coral breaks down, it leaves a pile of broken-up calciumwhich, on its own,

  • isn't that fertile.

  • But blast over some African dust and voila.

  • You've suddenly got nutrients in your soil, like magnesium, phosphorous, and potassium,

  • and things get a whole lot greener.

  • Dust nourishes soil all over the world, too, including in the Amazon rainforest and northern

  • Hawaiian islands.

  • So, on your next tropical vacation, you can thank dust for the scenery.

  • Now, all that might sound greatand it is.

  • But long-distance dust can also bring less welcome visitors, too, like pesticides and

  • metals.

  • For example, mercury made in China gets mixed in with the dust and blows east across the

  • Pacific.

  • Scientists have detected it in rivers and from the top of roughly 3 kilometer high at

  • Mt. Bachelor in Oregon.

  • They know it's from China because it has a specific chemical profile, but also because

  • the mercury only wafts in when the wind blows from the west.

  • So it's almost certainly coming from Chinese coal-fired power plants.

  • Mercury has plenty of ill effects on humans and ecosystems, including birth defects and

  • reproductive problems, so accumulating more of it in the water or soil isn't exactly

  • a great idea.

  • I mean, it's not great anywhere in the world, but it's harder to manage when it's blowing

  • all over the place.

  • Even without mercury, long-distance dust is also linked to problems with asthma and other

  • respiratory diseases.

  • That's because the particles that travel around the world tend to be especially fine

  • and harmful to lungs.

  • The dust can pick up some other hitchhikers, too, including live locusts and, most surprisingly,

  • microbes.

  • Until around 2000, scientists figured that intense ultraviolet radiation from the sun

  • would kill anything alive on its way across the ocean.

  • But they were wrong.

  • In a 2002 study from the journal American Scientist, researchers used petri dishes to

  • collect air samples in the Caribbean on an especially dusty day, and soon, microbes grew

  • in them.

  • Microbes aren't always bad, but altogether, about 20% of the ones found in international

  • dust have been linked to plant and animal diseases.

  • One microbe from Africa seems to be strongly linked to a disease killing fan coral in the

  • Caribbean.

  • Another is the same disease that causes diseases in Florida's carrots.

  • Even occasional human pathogens -- like ones linked to urinary tract or respiratory infections

  • -- can hitch a ride.

  • The scientists think that the microbes that survive the journey either have dark pigment,

  • which could act like sunscreen, or float near the bottom of the dust clouds where radiation

  • isn't as intense.

  • Enough attention is paid to these flying microbes that there's even a name for this field

  • of research: aeromicrobiology.

  • Now, flying dust might have a big impact on ecology, but its influence isn't just linked

  • to soil or plant diseases.

  • The dust can also interact with Earth's weatherlike how African dust weakens

  • hurricanes.

  • Yeah.

  • Hurricanes.

  • As the dust flies through the air, it can darken the clouds.

  • That reduces how much of the sun's heat reaches the Atlantic, and keeps the ocean

  • surface cooler.

  • That, in turn, suppresses hurricane formation, since warm ocean temperatures fuel the monster

  • storms.

  • So more dust equals fewer hurricanes.

  • This actually happened in 2006, when thick African dust caused the north Atlantic to

  • cool a third more than usual.

  • That year, only five hurricanes formed in the Atlantic compared to the 15 the year before

  • when there was less dust.

  • So, from fewer hurricanes to flying microbes, the global dust ecosystem is kind of a mixed

  • bag.

  • But one way or another, it's definitely cool.

  • Scientists are still working out what this vast, global migration of dust really means

  • like what it carries, and how, for better or worse, it's altering our world.

  • And with more tracking and more experiments, hopefully we'll find even more of those

  • weird effects soon.

  • Thanks for watching this episode of SciShow!

  • Besides causing problems on Earth, dust can cause even more trouble in spaceand in

  • fact, it's kind of an astronaut's worst enemy.

  • You can learn all about it over at SciShow Space.

  • [♩ OUTRO ]

[♩ INTRO ]

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B1 US dust soil african florida linked mercury

How African Dust Feeds Florida's Crops

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    joey joey posted on 2021/05/19
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