That dust that appears magically on your windowsill in Hawai'i?
It may be better-traveled than you are.
(Image: Here, airborne dust from the Sahara is seen as a brown haze over the Caribbean. The same thing happens in the Pacific, with dust from both Asia and South America. NOAA photo from the GOES8 satellite.)
There's a fair chance some of the material on the windowsill is Asia dust, lately resident of Chinese deserts or the smokestacks of China industry.
“Each year, long-distance winds drop up to 900 million tons of dust from the deserts and other parts of the land into the oceans,” write a team of researchers who have studied the issue.
Earlier work suggests Asian dust storms may have dumped enough material on the Islands to increase the fertility of worn-out volcanic soils. The most recent studies, looking at ocean sediments, suggest that dust volume is associated with climate change.
Researchers led by geochemist Gisela Winckler, of Columbia University's Lamont-Doherty Earth Observatory, studied seafloor sediments across 6000 miles of the Pacific south of Hawai'i—along the Equator from New Guinea to the Galapagos.
“Dust from Asia travels long ways, including Hawai'i and the West coast of the U.S., for example. In our study we present geochemical evidence that the dust in the central and western tropical Pacific (at the equator) is of Asian origin while the dust in the eastern equatorial Pacific is predominantly
derived from South America,” Winckler said in an email to RaisingIslands.
The paper, with the unfortunate title “Covariant glacial-interglacial dust fluxes in the equatorial Pacific and Antarctica,” was written by Winckler, Martin Fleisher, Robert Anderson and David McGee, all of Columbia, and Natalie Mahowald of Cornell. It was to be published today (Feb. 28) at the ScienceExpress website.
The dust is high in a range of nutrients—more on that later.
They used the isotope thorium 232 to track land dust—if you find this isotope in the remote ocean, it's generally from land-sourced dust. And they used various other isotopes to identify where the dust came from. Most on the western side of the Pacific came from Asia. On the Galapagos side, it tended to come from South America.
They also compared their data with information from previous cores done in Antarctica, where the main source of dust is Patagonia. Both sets of cores showed that during ice ages, there's a spike in the amount of continental dust deposited in the oceans.
Why do we care about dust? Because, as the paper says, “dust affects climate.” It may even be acting as a kind of feedback mechanism.
With more dust in the air, sunlight (and heat) is radiated back into space—helping keep the Earth's temperatures cool.
Dust has considerable amounts of iron, and it may fertilize the oceans, causing them to grow more plants and to suck carbon-dioxide out of the atmosphere. The reduced carbon-dioxide would lessen the atmosphere's ability to hold heat, and would further support cooling.
Other researchers have considered dumping iron into the oceans as a way of fertilizing them, causing themto take up more carbon-dioxide, all in hope that the stuff would sink to the deep sea and be hidden away for a long time. Winckler and her team, in a press release, say the jury is still out on how well that would work.
“A dozen early experiments in different regions have shown that plankton growth increases when iron is artificially added, but scientists have yet to show that this could lock significant amounts of CO2 into the ocean...The new data gives us a natural experiment to see what might have happened in the past.
They plan to study their sediment cores to see if they also include high levels of carbon, which might indicate carbon was effectively being sequestered.
The scientists say it's not entirely clear why there's more dust during ice ages, but it seems clear that there is a relationship between more cold and more dust.
Or, to let them use their own words:
“Although there is uncertainty concerning the complex interplay of the factors influencing dust generation in any particular region, we infer from the synchronous changes in dust fluxes seen in our records that in each of the source areas, i.e. Asia, northern South America and Patagonia, the dominant processes regulating dust generation experienced a coherent response to global climate change.”
© 2007 Jan W. TenBruggencate
