Link between Dust from Sahara and Amazon

 Dust from the Sahara keeps the Amazon rainforest alive

Scientists have just uncovered an incredible link between the world’s largest desert (the Sahara) and its largest rainforest (the Amazon). New research says that the Sahara Desert replenishes phosphorus in the Amazon rainforest via vast plumes of desert dust blowing over the Atlantic Ocean. Cold air pushing into the US may seem far removed from the soils of the Brazilian Amazon. Yet the atmosphere does not care about borders. This is a small world, and we’re all connected together. Air moves heat, water, smoke, dust and nutrients across oceans. Large weather systems can shape whether the Amazon receives air packed with African particles or air that has been scrubbed clean by rain over the Atlantic. The Amazon looks endlessly rich. Its trees grow thick, its rivers run wide and its wildlife is famous worldwide. But much of its soil is surprisingly poor in nutrients. Heavy rain washes minerals out of the upper soil layers, a process called leaching. Phosphorus is the biggest missing nutrient. Calcium, potassium and magnesium also run low. Part of the fix comes from far across the ocean: mineral dust from the Sahara Desert and smoke aerosols from biomass burning in Africa.

Although the richest spectacle of life on the planet, the Amazon rainforest is famous for its nutrient poor soils. Indeed, around 90% of the forest’s soils are low in phosphorous, which has long made intensive farming next-to-impossible in the region. Moreover, tens of thousand of tons of nitrogen wash away through river systems in the Amazon every year. So, how does the rainforest replenish its lost phosphorous? The researchers found that rainy days in the tropical Atlantic often lined up with cold air incursions into the US. High-pressure systems dominated the eastern US, while pressure also rose over the central and southern Atlantic. This setup strengthened low-level wind convergence near the equator. Moisture moved more strongly toward the Amazon. Rain increased. The air got cleaner before it reached the forest. We know that dust is very important in many ways. It is an essential component of the Earth system. Dust will affect climate and, at the same time, climate change will affect dust. Using data from a NASA satellite, it was estimated for the first time just how much dust reaches the Amazon from the Sahara Desert. According to the research, 27.7 million tons of dust on average ends up in the Amazon from the Sahara in what is described as the world’s largest transfer of dust.

Luiz Augusto Toledo Machado is a professor in the Physics Institute at the University of São Paulo and a collaborator with the Department of Chemistry at the Max Planck Institute in Germany. “The results demonstrate that there’s an interconnection, a symbiosis of life on the planet. Climate change affects this pattern, causing a disruption whose outcome and consequences for future ecosystems are still unknown,” said Machado. Researchers used daily black carbon measurements from the Amazon Tall Tower Observatory, a 1,066-foot tower in the Uatumã Sustainable Development Reserve in Brazil. The tower tracks meteorological, chemical and biological data, including greenhouse gases. Black carbon is soot from burning fuel and biomass. During the rainy season, it helps scientists track long-distance particle transport. According to Machado, approximately 60% of the black carbon that reaches the Amazon during the rainy season originates in Africa. This is important because a tiny percentage of that dust, 0.08%, is phosphorous, but just enough to make a big difference. Overall, the scientists estimate that the amount of phosphorus reaching the Amazon annually from the Sahara, 22,000 tons, equals about how much the rainforest loses to rivers.

The team studied daily black carbon levels in January and February from 2015 to 2022, the start of the Amazon rainy season. Some days carried strong African influence. Other days were unusually clean. The key surprise was rain over the tropical Atlantic. Clean days over the Amazon came after peak rainfall over the ocean. Earlier thinking leaned toward wind direction as the main reason for these changes. This study points to a larger weather pattern. It adds a sharp detail to a bigger story: forests, deserts, oceans and weather systems are linked in ways that are easy to miss. A cold spell in one place can help change the mix of particles reaching another place thousands of miles away. Machado also pointed to earlier research showing that low phosphorus can limit Amazon growth even when the air has more CO2. It matters because faster plant growth can help pull carbon from the atmosphere. Later maps made with artificial intelligence confirmed low phosphorus levels across the region.

Contrary to what one might imagine, this region is very important for the health of the planet. Its dust contains crucial minerals not only for fertilizing the Amazon, but also for sustaining aquatic life. Among them are iron and phosphorus, which are fundamental for forest productivity and life in the oceans. This suggests that African dust may have important implication for maintaining the health of Amazon rainforests over the long term. Without the phosphorus input from African dust, the hydrological loss would greatly deplete the soil phosphorus reservoir over a time scale of decades or centuries and affect the health and productivity of the Amazon rainforest, but researchers also caution that they still don’t know the amount of dust needed to provide adequate phosphorus for maintaining the productivity of the Amazon rainforest. Particles and gases usually travel from Africa above the marine boundary layer, the lower part of the atmosphere that touches the ocean. The Amazon’s low-level jet stream then helps move them into the basin. Changes in these low-level jets could shift how much dust and smoke reach the forest. This could affect the Amazon’s long-term strength, especially as climate change alters rainfall, pressure systems, and wind patterns.

The scientists believe the most important source of phosphorous for the Amazon is dust whipped up from the Bodélé Depression in Chad. The frequent dust storms from this ancient lake bed contain massive amounts of dead microorganisms and, as such, are super-rich in phosphorus. The researchers also found that the amount of dust reaching the Amazon from the Sahara was hugely variable during the years of research. They theorize that rainfall in the Sahel, a vast region of drylands just south of the Sahara, may be responsible for the variation, though they note that more long term research is needed to have some conclusive theory.

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Non-Rotating Galaxy found

 A giant galaxy that doesn’t spin is a surprise to astronomers     

Using instruments on the James Webb Space Telescope, astronomers can measure the movement of mass inside galaxies less than two billion years after the Big Bang. To their surprise, astronomers discovered a galaxy that is not rotating as would be expected at that age of the Universe. Astronomers using the James Webb Space Telescope have made a surprising discovery about a galaxy long, long ago and far, far away, It isn’t rotating. That’s something only seen in the most massive, mature galaxies that are closer to us in space and time, said Ben Forrest, a research scientist in the Department of Physics and Astronomy at the University of California, Davis, and first author of the paper.  Astronomers using the James Webb Space Telescope spotted something that shouldn’t exist, at least not so early in the universe. A massive galaxy, formed less than 2 billion years after the Big Bang, appears to have no rotation at all, a trait usually seen only in much older, evolved galaxies. This challenges current theories that young galaxies should still be spinning from their formation.

“This one in particular did not show any evidence of rotation, which was surprising and very interesting,” Forrest said. According to current theories, as the first galaxies formed, angular momentum from inflowing gas and the influence of gravity set them spinning. A giant ancient galaxy that mysteriously doesn’t spin is rewriting what we thought we knew about how galaxies form. Despite forming when the universe was still very young, this galaxy shows no signs of rotation. This behavior is typically seen only in very large, mature galaxies much closer to Earth, explained Ben Forrest. "This one in particular did not show any evidence of rotation, which was surprising and very interesting," Forrest said. The research was supported by grants from NASA, the Space Telescope Science Institute, and the National Science Foundation. Over many billions of years, some galaxies, especially those within galaxy clusters, merged with each other multiple times and their combined rotations added to or partly canceled each other. That’s why some galaxies which are closest to Earth (and therefore also relatively recent) can show little overall rotation but a lot of random movement of stars within them. This process should take an enormously long time, so it’s surprising that galaxy XMM-VID1-2075 had achieved this state when the universe was less than 2 billion years old. 

Using the James Webb Space Telescope, the team examined XMM-VID1-2075 alongside two other galaxies from the same era. This allowed them to track how material moves within each system. "This type of work has been done a lot with nearby galaxies because they're closer and larger and so you can do these kinds of studies from the ground, but it's very difficult to do with high redshift galaxies because they appear a lot smaller in the sky," Forrest said. "James Webb Space Telescope is really pushing the frontier for these kinds of studies." Among the three galaxies, one clearly rotates, another shows irregular structure and the third shows no rotation but strong random motion of its stars. "That's consistent with some of the most massive galaxies in the local universe, but it was a bit surprising to find it so early on," Forrest said.

Forrest and colleagues in the MAGAZ3NE (Massive Ancient Galaxies at z>3 NEar-Infrared) survey had previously observed this galaxy with the W.M. Keck observatory in Hawaiʻi. “Previous MAGAZ3NE observations had confirmed this was one of the most massive galaxies in the early universe, with already several times as many stars as our Milky Way, and also confirmed that it was no longer forming new stars, making it a compelling target for follow-up observations,” Forrest said. Current models suggest that galaxies begin spinning as they form. Gas flowing inward and the pull of gravity create angular momentum, setting these systems in motion. Galaxies can collide and merge, especially in dense clusters. These repeated interactions can either build up or cancel out rotation. As a result, some nearby galaxies show little overall spin and instead display stars moving in random directions. Because this transformation is thought to take a very long time, it is surprising to see it in galaxy XMM-VID1-2075 when the universe was less than 2 billion years old.

The team were able to measure the relative movement of material inside them. Researchers are now trying to understand how this galaxy became what scientists call a "slow rotator" so quickly. One possible explanation is not a long history of multiple mergers, but a single dramatic collision. If two galaxies spinning in nearly opposite directions collided, their motions could cancel out. Of the three galaxies they sampled, one is clearly rotating, one is “kind of messy,” and one has no rotation but a lot of random motion, Forrest said. The XMM-VID1-2075 shows a lack of rotational movement compared to the other two galaxies. How did this galaxy become a “slow rotator” in less than 2 billion years? One possibility is that it is the result not of multiple mergers, but a single collision between two galaxies rotating pretty much in opposite directions. That idea is supported by the team’s observations. “For this particular galaxy, we see a large excess of light off to the side. And so that's suggestive of some other object which has come in and is interacting with the system and potentially changing its dynamics,” Forrest said.

The astronomers are continuing to search for similar galaxies in the early universe. By comparing observations with computer simulations, scientists can test whether current theories of galaxy formation hold up. "There are some simulations that predict that there will be a very small number of these non-rotating galaxies very early in the universe, but they expect them to be quite rare. And so this is one way in which we can test these simulations and really figure out how common they are, and that can then give us information about whether our theories of this evolution are correct," Forrest said. 

Muhammad (Peace be upon him) Name