S Asian black carbon aerosols increase glacial mass loss in Tibet Study (GS Paper 3, Environment)
Why in news?
- Black carbon aerosols have indirectly affected the mass gain of the Tibetan Plateau glaciers by changing long-range water vapour transport from the South Asian monsoon region, a study has found.
- The South Asia region adjacent to the Tibetan Plateau has among the highest levels of black carbon emission in the world.
Black carbon:
- Black carbon aerosols are produced by the incomplete combustion of fossil fuels and biomass, and are characterised by strong light absorption.
- Many studies have emphasised black carbon aerosols from South Asia can be transported across the Himalayas to the inland region of the Tibetan Plateau.
Observations made:
- Researchers noted that black carbon deposition in snow reduces the albedo of surfaces, a measure of how much of Sun's radiations are reflected, which may accelerate the melting of glaciers and snow cover, thus changing the hydrological process and water resources in the region.
- The study found that since the 21st century, South Asian black carbon aerosols have indirectly affected the mass gain of the Tibetan Plateau glaciers by changing long-range water vapour transport from the South Asian monsoon region.
Impact:
- Black carbon aerosols in South Asia heat up the middle and upper atmosphere, thus increasing the NorthSouth temperature gradient.
- Accordingly, the convective activity in South Asia is enhanced, which causes convergence of water vapour in South Asia. Meanwhile, black carbon also increases the number of cloud condensation nuclei in the atmosphere.
- These changes in meteorological conditions caused by black carbon aerosols make more water vapour form precipitation in South Asia, and the northward transport to the Tibetan Plateau was weakened.
- As a result, precipitation in the central and the southern Tibetan Plateau decreases during the monsoon, especially in the southern Tibetan Plateau.
- The decrease in precipitation further leads to a decrease of mass gain of glaciers. From 2007 to 2016, the reduced mass gain by precipitation decrease accounted for 11 per cent of the average glacier mass loss on the Tibetan Plateau and 22.1 per cent in the Himalayas.
What’s next?
- The transboundary transport and deposition of black carbon aerosols from South Asia accelerate glacier ablation over the Tibetan Plateau.
- Meanwhile, the reduction of summer precipitation over the Tibetan Plateau will reduce the mass gain of plateau glaciers, which will increase the amount of glacier mass deficit.
A new coronavirus variant on the block
(GS Paper 2, Health)
Context:
- India’s first case of the XBB.1.5 subvariant of Omicron was confirmed in Gujarat by the national genome sequencing consortium on December 31.
- XBB.1.5 has been driving COVID-19 cases in the U.S. Studies of the strain indicate that it is highly transmissible and evades pre-existing immunity. Yet it doesn’t seem to cause severe disease.
- The global prevalence of XBB.1.5 isn’t clear yet, although its parent strain has been detected in at least 35 countries.
How did the variant begin?
- XBB.1.5 is a recombinant, which means its genome is the product of the genomes of two different strains spliced together. This can happen when two strains infect a person at the same time; a recombinant variant is produced as they replicate together.
- Recombinant strains also arise when existing recombinant strains mutate. Previous recombinants include XD (Delta + Omicron), XE (BA.1 + BA.2), and XBB (BA.2.10.1 + BA.2.75). The XBB strain is descended from BA.2.10.1.1 and BA.2.75.3.1.1.1.
- It mutated further and became XBB.1.5. XBB.1, which also descended from XBB, accounted for 14% of new cases in India around mid-December 2022.
How transmissible is it?
- XBB.1.5 is as immune-evasive as XBB.1. Both XBB and XBB.1 were more immune-evasive than BA.5.2 (its descendant BF.7 is surging in China) and in fact are the most evasive strains so far.
- XBB.1.5 is better at binding to ACE2 receptors in the body than XBB or XBB.1. So XBB.1.5 is more transmissible. There is already empirical data to show that it spreads faster than BQ.1.1, the subvariant that it displaced in the U.S. as the dominant strain.
- However, that XBB.1.5’s ACE2 binding affinity is comparable to that of BA.2.75, the Omicron sub-variant detected in India in May 2022. The transmissibility of XBB.1.5 is otherwise still high: it allows the virus to spread more, giving it more opportunities to mutate to more potent forms.
- XBB.1.5 has an ACE2 binding affinity similar to that of BA.2.75, could be more transmissible than XBB and XBB.1, and be as immune-evading as the two.
- Overall, it has a high growth advantage. And so far, it doesn’t appear to be able to cause severe disease.
What are the implications for India?
- Variants would have been of some concern if the virus’s transmission wasn’t ongoing; however, as most settings have continuous virus transmission without clinical disease, even reduced efficacy against new variants in the real world has been compensated for by natural infections and booster doses.
- The research on new vaccines should continue but that it shouldn’t peg them to newer sub-variants: by the time such vaccines are made available, a new subvariant might emerge.
Rhinos dispersed across South, Central Asia via Tibet Study
(GS Paper 3, Environment)
Why in news?
- The giant rhino, Paraceratherium, was the largest land mammal that ever lived and was found primarily in Asia, particularly in China, Mongolia, Kazakhstan, and Pakistan.
- However, it was long unknown how this genus spread across Asia. A recent discovery has shed new light on this process.
New species:
- Researchers recently, reported a new species, Paraceratherium linxiaense sp. nov., which offers important clues to the dispersal of giant rhinos across Asia.
- The new species’ fossils comprise a completely preserved skull and mandible with their associated atlas, as well as an axis and two thoracic vertebrae from another individual.
- The fossils were recovered from the Late Oligocene deposits of the Linxia Basin in Gansu Province, China, which is located on the northeastern border of the Tibetan Plateau.
- Phylogenetic analysis yielded a single most parsimonious tree, which places P. linxiaense as a derived giant rhino, within the monophyletic clade of the Oligocene Asian Paraceratherium.
Six species:
- Within the Paraceratherium clade, the researchers’ phylogenetic analysis produced a series of progressively more-derived species–from P. grangeri, through P. huangheense, P. asiaticum, and P. bugtiense–finally terminating in P. lepidum and P. linxiaense.
- P. linxiaense is at a high level of specialization, similar to P. lepidum, and both are derived from P. bugtiense.
- Adaptation of the atlas and axis to the large body and long neck of the giant rhino already characterized P. grangeri and P. bugtiense, and was further developed in P. linxiaense, whose atlas is elongated, indicative of a long neck and higher axis with a nearly horizontal position for its posterior articular face. These features are correlated with a more flexible neck.
- The giant rhino of western Pakistan is from the Oligocene strata, representing a single species, Paraceratherium bugtiense. On the other hand, the rest of the genus Paraceratherium, which is distributed across the Mongolian Plateau, northwestern China, and the area north of the Tibetan Plateau to Kazakhstan, is highly diversified.
Findings:
- The researchers found that all six species of Paraceratherium are sisters to Aralotherium and form a monophyletic clade in which P. grangeri is the most primitive, succeeded by P. huangheense and P. asiaticum.
- The researchers were thus able to determine that, in the Early Oligocene, P. asiaticum dispersed westward to Kazakhstan and its descendant lineage expanded to South Asia as P. bugtiense. In the Late Oligocene, Paraceratherium returned northward, crossing the Tibetan area to produce P. lepidium to the west in Kazakhstan and P. linxiaense to the east in the Linxia Basin.
Migration in Oligocene:
- The researchers noted the aridity of the Early Oligocene in Central Asia at a time when South Asia was relatively moist, with a mosaic of forested and open landscapes. Late Oligocene tropical conditions allowed the giant rhino to return northward to Central Asia, implying that the Tibetan region was still not uplifted as a high-elevation plateau.
- During the Oligocene, the giant rhino could obviously disperse freely from the Mongolian Plateau to South Asia along the eastern coast of the Tethys Ocean and perhaps through Tibet.
- The topographical possibility that the giant rhino crossed the Tibetan area to reach the Indian-Pakistani subcontinent in the Oligocene can also be supported by other evidence.
- Up to the Late Oligocene, the evolution and migration from P. bugtiense to P. linxiaense and P. lepidum show that the “Tibetan Plateau” was not yet a barrier to the movement of the largest land mammal.
