Warmer Ocean Temperatures May Decrease Saharan Dust Crossing the Atlantic
Narration: Lara Streiff
Transcript:
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Earth is a system
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of systems. That means that even small changes
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in one part of the planet can have effects felt all the way around the globe.
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The world’s largest,
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hottest desert --the Sahara -- is nearly the size of the continental United States.
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Each year millions of tons of its nutrient-laden
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dust are swirled up into the atmosphere by easterly trade winds,
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and carried across the Atlantic. The plumes can make
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their way from the African continent as far as the Amazon rainforest,
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where they fertilize the plant life of one of Earth’s most biodiverse regions.
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The dust carries phosphorus, a nutrient necessary
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for plant growth. As it travels around
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the globe, the resultant layer of dust can easily be seen from space.
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This was especially true over the month of June 2020,
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when satellites and astronauts observed an unusually large quantity
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of dust, nicknamed the Godzilla plume, heading west from Northern Africa.
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It thinned out over its 3000-mile
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mile journey, depositing nutrients into the ocean and land below.
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To travel such a distance requires strong winds.
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These winds are from the trade wind system. The trade winds are affected
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by differences in sea surface temperature between the northern and southern Atlantic Ocean.
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Over the last century, the North Atlantic
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Ocean has experienced a shift in sea surface temperature every few decades,
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referred to as the Atlantic Multidecadal Oscillation,
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or the Atlantic Multidecadal Variability.
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Warmer sea surface temperatures in the north, like those observed in recent years,
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lower the contrast between north and south and change wind circulation,
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slowing the trade winds down.
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The northern and southern trade winds converge along a latitudinal band called the
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the Intertropical Convergence Zone, or ITCZ, which is where
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rainfall is most concentrated in the region. The ITCZ
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and its connection to sea surface temperature and
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wind has been supported by observations over thousands of years.
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Though the band of rain always moves north and south
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with the seasons, a recent NASA study shows that the ITCZ
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has been migrating farther and farther north over the last several decades,
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likely a result of the warming climate. As the band covers more of the Sahara,
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increased quantities of rainfall over the desert dampen down
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the dust, making it less likely to be carried off by the already
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weakened winds. As the climate changes,
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dust activity will continue to be affected. NASA researchers
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predict that within the next century we will see dust transport
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approach a 20,000-year minimum.
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NASA