Tyler O'Neal, Staff Editor

CNRS researcher Pierron's supercomputer-simulated genetic data shows human expansion 1,000 years ago linked to Madagascar’s loss of large vertebrates

Current anthropized landscape of Madagascar CREDIT MAGE ConsortiumThe island of Madagascar—one of the last large land masses colonized by humans—sits about 250 miles (400 kilometers) off the coast of East Africa. While it’s still regarded as a place of unique biodiversity, Madagascar long ago lost all its large-bodied vertebrates, including giant lemurs, elephant birds, turtles, and hippopotami. A human genetic study reported in the journal Current Biology on November 4 links these losses in time with the first major expansion of humans on the island, around 1,000 years ago.

“This human demographic expansion was simultaneous with a cultural and ecological transition on the island,” says Denis Pierron, French National Centre for Scientific Research (CNRS) researcher in Toulouse, France. “Around the same period, cities appeared in Madagascar and all the vertebrates of more than 10 kilograms disappeared.”

The origins of humans in Madagascar have long been an enigma, Pierron explained. Madagascar is home to 25 million people who speak an Asian language despite the island’s proximity to East Africa. Other groups who speak similar languages live more than 4,000 miles away. The people that live in Madagascar are known to trace their roots back to two small populations: one Bantu-speaking from Africa and another Austronesian-speaking from Asia. But, beyond that, the history remained rather murky.

To retrace the history and understand more about the origin of the Malagasy people, a multi-disciplinary consortium launched 2007 a project known as Madagascar Genetic and Ethnolinguistic (MAGE). Over 10 years, Malagasy and international researchers visited more than 250 villages across the country to sample the cultural and genetic human diversity.

In the new study, Pierron and his colleagues took a close look at the human genetic evidence. More specifically, they closely studied how various segments of human chromosomes were shared with local ancestry information and supercomputer-simulated genetic data. Together, they’ve inferred that the Malagasy ancestral Asian population was isolated on the island for more than 1,000 years with an effective population size of just a few hundred individuals.

Their isolation ended about 1,000 years ago when a small group of Bantu-speaking African people came to Madagascar. Afterward, the population continued to expand rapidly over generations. The growing human population led to extensive changes to the Madagascar landscape and the loss of all large-bodied vertebrates that once lived there, they suggest.

The findings have important implications that may now be applied to studies of other human populations. For instance, it shows it’s possible to untangle the demographic history of ancient populations even well after two or more groups have mixed, by using genetic data and supercomputer simulations to test the likelihood of different scenarios. The findings also offer new insights into how past changes in human populations led to changes in whole ecosystems.

“Our study supports the theory that it was not directly the arrival of humans on the island that caused the disappearance of the megafauna, but rather a change in lifestyle that caused both a human population expansion and a reduction in biodiversity in Madagascar,” Pierron says.

While these efforts have led to a much better understanding of Madagascar’s history, many intriguing questions remain. For instance, Pierron asks, “If the ancestral Asian population was isolated for more than a millennium before mixing with the African population, where was this population? Already in Madagascar or in Asia? Why did the Asian population isolate itself over 2,000 years ago? Around 1,000 years ago, what triggered the observed cultural and demographic transition?” 

British Antarctic Survey demos new link between greenhouse gasses, sea-level rise

Tyler O'Neal, Staff Editor

A new study provides the first evidence that rising greenhouse gases have a long-term warming effect on the Amundsen Sea in West Antarctica.  Scientists from British Antarctic Survey (BAS) say that while others have proposed this link, no one has been able to demonstrate it.

Ice loss from the West Antarctic Ice Sheet in the Amundsen Sea is one of the fastest-growing and most concerning contributions to global sea-level rise.  If the West Antarctic Ice Sheet were to melt, global sea levels could rise by up to three meters.  The patterns of ice loss suggest that the ocean may have been warming in the Amundsen Sea over the past one hundred years, but scientific observations of the region only began in 1994.                        

In the study - published in the journal Geophysical Research Letters - oceanographers used advanced supercomputer modeling to simulate the response of the ocean to a range of possible changes in the atmosphere between 1920 and 2013.

The simulations show the Amundsen Sea generally became warmer over the century. This warming corresponds with simulated trends in wind patterns in the region which increase temperatures by driving warm water currents towards and beneath the ice. Rising greenhouse gases are known to make these wind patterns more likely, and so the trend in winds is thought to be caused in part by human activity. 

This study supports theories that ocean temperatures in the Amundsen Sea have been rising since before records began.  It also provides the missing link between ocean warming and wind trends which are known to be partly driven by greenhouse gasses.  Ocean temperatures around the West Antarctic Ice Sheet will probably continue to rise if greenhouse gas emissions increase, with consequences for ice melt and global sea levels.  These findings suggest, however, that this trend could be curbed if emissions are sufficiently reduced and wind patterns in the region are stabilized.

Dr. Kaitlin Naughten, an ocean-ice modeler at BAS and lead author of this study, says,

“Our simulations show how the Amundsen Sea responds to long-term trends in the atmosphere, specifically the Southern Hemisphere westerly winds.  This raises concerns for the future because we know these winds are affected by greenhouse gases.  However, it should also give us hope, because it shows that sea-level rise is not out of our control.”

Professor Paul Holland, ocean and ice scientist at BAS and a co-author of the study, says,

“Changes in the Southern Hemisphere westerly winds are a well-established climate response to the effect of greenhouse gasses.  However, the Amundsen Sea is also subject to very strong natural climate variability.  The simulations suggest that both natural and anthropogenic changes are responsible for the ocean-driven ice loss from the West Antarctic Ice Sheet.”

China applies mesoscale drag to improve the CFD model for simulating the flue gas desulfurization process in powder-particle spouted beds

Tyler O'Neal, Staff Editor

Sulfur dioxide is the main source of air pollution and easily forms a haze deteriorating the air quality. Therefore, various studies on the reduction of sulfide emissions generated during fossil combustion have been performed. Among them, the semi-dry flue gas desulfurization technology in powder-particle spouted beds (PPSBs) is considered a reliable and effective desulfurization method. Schematic diagram of desulfurization mechanism in powder-particle spouted bed CREDIT Feng Wu

With the development of computational fluid dynamics (CFD) methods, an increasing number of researchers conducted numerical simulations of the desulfurization of semi-dry flue gas in a spouted bed. Such a bed involves a multiphase flow and heat and mass transfer, including a gas-solid two-phase flow, a water vaporization process, and a desulfurization reaction. However, the current homogeneous drag models (such as the Gidaspow and Wen-Yu ones) used in simulations did not consider the influence of the mesoscale structure during drag coefficient calculations, resulting in a severe overestimation of the drag, which hurt simulation accuracy. To solve this problem, Feng Wu and his team modified the heterogeneous gas-solid drag model and applied it to the simulation of the two-dimensional spouted bed. The relevant work was published online in Frontiers of Chemical Science and Engineering on December 9, 2021.

In this study, by simulating and analyzing the gas-solid two-phase flow coupled water vaporization and desulfurization process of the spouted bed, they found that the adjusted mesoscale drag model can accurately and effectively describe the semi-dry flue gas desulfurization process in the spouted bed. There is a structure-activity relationship between the drag model and the heat transfer, mass transfer, and desulfurization reaction.

The obtained results revealed that the particle velocity simulated by the modified mesoscale model is more consistent with the experimental data. The spout morphology simulated by the adjusted mesoscale drag model was unstable and discontinuous bubbling spout unlike the stable continuous spout obtained using the Gidaspow model. The bubbling spout state conforms to physical reality.

The water distribution in the spouted bed simulated by the EMMS drag model was uniform, and its water vaporization rate was larger than that determined by the Gidaspow drag model. The mass fraction of water in the gas at the outlet obtained by the heterogeneous drag model was 1.5 times greater than estimated by the homogeneous drag model during the simulation of water vaporization.

For the desulfurization reaction, the experimental desulfurization efficiency was 75.03%, while the simulated desulfurization efficiencies obtained by the Gidaspow and adjusted mesoscale drag models were 47.63% and 75.08%, respectively, indicating much higher accuracy of the latter technique.

Feng Wu and his team will further expand the adjusted mesoscale drag model to three dimensions to obtain more relationships between drag models and heat and mass transfer.