National Geographic calls Ethiopia's Danakil Depression "the cruelest place on Earth." It's a desert wasteland, where temperatures can push past 120 F, where ancient and current lava flows impede movement, and where water is so scarce that that people build rock domes over the top of volcanic vents to trap and condense steam.
It's also a place where Ethiopian men and boys regularly travel in order to cut slabs of salt off of the surface of the Earth and haul them back to civilization. Salt flats like this occur when entire bodies of water totally evaporate. In the Danakil Depression, you'll also find salt towers and other formations caused by evaporation off of volcanic geysers and hot springs.
The photo above was taken by Reuters photographer Siegfried Modola, who traveled with a group of salt miners into the desert and then followed their haul all the way back to the marketplace. You can see his full slideshow of images online. I chose this one because it gives you a view of the salt as it's found on the ground, and the neat, rectangular blocks the merchants cut it into for shipping.
The spot is a favorite of photographers. I'd also recommend checking out the photos and story put together by Christina Feldt, who posted about the Danakil salt flats earlier this year.
On Monday, I posted about an incredibly fascinating study linking the minerals that fertilize the Amazon rainforest to a specific corner of the Sahara desert in the country of Chad. That lake of sand—once an actual lake the size of California—is what keeps the Amazon green and verdant.
The interesting thing is that the study is actually not anything new. It came out in 2006. I heard about it from science writer Colin Schultz. Earlier this week, Colin went on News Talk 610 CKTB out of Niagara Falls, Ontario, to talk about how he stumbled across the study and why it's important far beyond simply connecting the desert and the jungle.
The interview delves into the subject in a lot more depth. In fact, it's a great demonstration of how reading a single research paper can be interesting, but doesn't necessarily give you the full picture of what's actually going on in science. Turns out, what we know about how dust travels to the Amazon has important implications for how we think about climate change and geoengineering. Also great: Colin comparing the volume of dust traveling from the Sahara to the volume of several Honda Civics. It's short, and very much worth listening to.
You can follow Colin Schultz on Twitter. BTW: He'd like you to know that when he says "bioengineers" in the interview, he means "geoengineers".
• A 2010 Nature News article on the connection between the Sahara and the Amazon.
• Geophysical Research Letters on changes in dust transport over time.
• NASA on the way that dust affects climate.
• A 2010 follow-up to the 2006 paper by the same group of researchers. Colin says that this gets more into the details of how the dust becomes an important fertilizer in the Amazon.
This is probably the most amazing thing I learned all weekend. The Amazon rainforest—with all its plant and animal life, and all its astounding biodiversity—could not exist as we know it without the patch of African desert pictured above.
The rainforest is amazing, but the soil it produces isn't very nutrient rich. All the minerals and nutrients that fertilize the rainforest have to come from someplace else. Specifically: Africa. Scientists have known for a while that this natural fertilizer is crossing the Atlantic in the form of dust storms, but science writer Colin Schultz ran across a 2006 paper in the journal Environmental Research Letters that not only produces evidence for a much larger trans-oceanic transfer of dust than was previously assumed ... it also pinpoints the exact (and astoundingly small) location where all the fertilizer in the Amazon is coming from.
The research paper, itself, is pleasantly readable, as far as these things go, so I'm going to quote directly from it. One quick note before I launch into this quote. The authors are measuring the mass of the dust in teragrams (or Tg). As you're trying to wrap your head around this, it might be helpful to know that 1 Tg = 1 million tons.
A total of 140 (± 40) Tg is deposited in the Atlantic ocean and 50 (± 15) Tg reach and fertilize the Amazon basin. This is four times an older estimate, explaining a paradox regarding the source of nutrients to the Amazon forest. Swap et al suggested that while the source for minerals and nutrients in the Amazon is the dust from Africa, it was estimated that only 13 Tg of dust per year actually arrive in the Amazon. However, they pointed out that 50 Tg are needed to balance the Amazon nutrient budget.
Here we show a remarkable arrangement in nature in which the mineral dust arriving at the Amazon basin from the Sahara actually originates from a single source of only ~ 0.5% of the size of the Amazon: the Bodélé depression. Located northeast of Lake Chad (17°N, 18°E) near the northern border of the Sahel, it is known to be the most vigorous source for dust over the entire globe.
Basically, these 2006 calculations account for all the fertilization needs of the Amazon, while previous calculations left a weird gap in between the amount of dust the rainforest needed and the amount the scientists thought was getting there.
Also: The place the dust is coming from is a single, highly specific region. As Alexis Madrigal pointed out at The Atlantic, we're talking about a patch of desert only 1/3 the size of Florida supplying the nutrient needs of a jungle that is roughly the same size as all 48 contiguous United States. Mind, blown.
Read the full research paper at Environmental Research Letters
Check out The Atlantic's write up on this, including a satellite photo of the dust storms in question.
Follow the guy who started it all—the very smart, very entertaining, and very tall Colin Schultz
Via Bart King