1. OVERTURNING CIRCULATION
TAG: GS 1: GEOGRAPHY
CONTEXT: Antarctica sets the stage for the world’s greatest waterfall. The action takes place beneath the surface of the ocean. Here, trillions of tonnes of cold, dense, oxygen-rich water cascade off the continental shelf and sink to great depths. This Antarctic “bottom water” then spreads north along the sea floor in deep ocean currents, before slowly rising, thousands of kilometres away. Antarctica drives a global network of ocean currents called the “overturning circulation” that redistributes heat, carbon and nutrients around the globe.
EXPLANATION:
What is Overturning circulation?
- The ocean’s water is constantly circulated by currents.
- Tidal currents occur close to shore and are influenced by the sun and moon. Surface currents are influenced by the wind. However, other, much slower currents that occur from the surface to the seafloor are driven by changes in the saltiness and ocean temperature.
- The overturning is crucial to keep the earth’s climate stable.
- It is also the main way oxygen reaches the deep ocean.
Effects of overturning circulation:
- Melting of Antarctic ice is disrupting the formation of Antarctic bottom water. As the flow of bottom water slows, the supply of oxygen to the deep ocean declines. The shrinking oxygen-rich bottom water layer is then replaced by warmer waters that are lower in oxygen, further reducing oxygen levels.
- Ocean animals, large and small, respond to even small changes in oxygen. Deep-ocean animals are adapted to low oxygen conditions but still have to breathe. Losses of oxygen may cause them to seek refuge in other regions or adapt their behaviour.
- Slowdown of the overturning may also intensify global warming. The overturning circulation carries carbon dioxide and heat to the deep ocean, where it is stored and hidden from the atmosphere. As the ocean storage capacity is reduced, more carbon dioxide and heat are left in the atmosphere. This feedback accelerates global warming.
- Reductions in the amount of Antarctic bottom water reaching the ocean floor also increases sea levels because the warmer water that replaces it takes up more space (thermal expansion).
How is this happening?
- Overturning circulation has slowed by almost a third (30%) and deep ocean oxygen levels are declining.
- This slowdown has the potential to disrupt the connection between the Antarctic coasts and the deep ocean.
- Melting of Antarctic ice is disrupting the formation of Antarctic bottom water. The meltwater makes Antarctic surface waters fresher, less dense, and therefore less likely to sink. This puts the brakes on the overturning circulation.
How was it measured?
- The full-depth measurements collected by ships provide snapshots of ocean density but are usually repeated about once a decade.
- Moored instruments, on the other hand, provide continuous measurements of density and speed, but only for a limited time at a particular location.
- A new approach that combines ship data, mooring records, and a high resolution numerical simulation to calculate the strength of Antarctic bottom water flow and how much oxygen it transports to the deep ocean.
Atlantic Meridional Overturning Circulation (AMOC):
- The AMOC circulates water from north to south and back in a long cycle within the Atlantic Ocean. This circulation brings warmth to various parts of the globe and also carries nutrients necessary to sustain ocean life.
- The circulation process begins as warm water near the surface moves toward the poles (such as the Gulf Stream in the North Atlantic), where it cools and forms sea ice. As this ice forms, salt is left behind in the ocean water.
- Due to the large amount of salt in the water, it becomes denser, sinks down, and is carried southwards in the depths below. Eventually, the water gets pulled back up towards the surface and warms up in a process called upwelling, completing the cycle.
- The entire circulation cycle of the AMOC, and the global conveyor belt, is quite slow. It takes an estimated 1,000 years for a parcel (any given cubic meter) of water to complete its journey along the belt.
- Even though the whole process is slow on its own, there is some evidence that the AMOC is slowing down further. NOAA funds research to better understand this potential slowing, as well as to investigate the AMOC’s role in coastal sea level changes and its relationship to extreme events.
2. CHEETAH
TAG: GS 3: ENVIRONMENT AND ECOLOGY
CONTEXT: Almost 70 years after the Asiatic cheetah (Acinonyx jubatus venaticus) went extinct in India, eight cheetahs from Namibia and 12 from South Africa were introduced into the Kuno National Park in Madhya Pradesh in September 2022 and February 2023, respectively. The intent was to establish a free-ranging population of cheetahs belonging to the subspecies, Acinonyx jubatus. Recent Study states that Cheetahs introduced without considering spatial ecology. Ideally, just one cheetah is present in 100 sq. km. of an unfenced area, whereas the density of Cheetahs in the Kuno national park stands at three per 100 sq. km.
EXPLANATION:
- Cheetahs fulfil a unique ecological role within the carnivore hierarchy and their restoration is expected to enhance ecosystem health in India.
- As a charismatic species, the cheetah can also benefit India’s broader conservation goals by improving general protection and ecotourism in areas that have been previously neglected.
Project Cheetah:
- The Union environment ministry’s National Tiger Conservation Authority (NTCA) implements Project Cheetah.
- The project hopes to benefit global cheetah conservation efforts by providing up to 100 000 km2 of habitat in legally protected areas and an additional 600 000 km2 of habitable landscape for the species.
Body characteristics:
- The cheetah is a sexually dimorphic species though it is difficult to identify cheetahs’ sex by appearance alone. Male cheetahs are slightly bigger than females and they have larger heads, but they do not display the same degree of physical difference between the sexes of other big cat species like lions.
- Cheetahs have a thin frame with a narrow waist and deep chest. They have large nostrils that allow for increased oxygen intake. Cheetahs have a large lungs and hearts connected to a circulatory system with strong arteries and adrenals that work in tandem to circulate oxygen through their blood very efficiently.
- With its long legs and very slender body, the cheetah is quite different from all other cats and is the only member of its genus, Acinonyx. The cheetah’s unique morphology and physiology allow it to attain the extreme speeds for which it’s famous.
- The gestation (pregnancy) period for the cheetah is 93 days, and litters range in size from one or two up to six cubs (the occasional litter of eight cubs has been recorded, but it is rare).
- Cheetahs prey includes: gazelles (especially Thomson’s gazelles), impalas and other small to medium-sized antelopes, hares, birds, and rodents. Cheetahs will also prey on the calves of larger herd animals.
Species of Cheetah:
- Widely regarded as the fastest animal on land, cheetahs are divided into four subspecies; the Southeast African cheetah, the Northeast African cheetah, the Northwest African cheetah, and the rare Asiatic cheetah.
Asiatic and African cheetah:
- The Asiatic cheetah is slightly smaller and slender than the African cheetah. The neck is much smaller and longer.
- The Asiatic cheetah has a buff to light fawn color bordering on pale yellow skin, and it has more fur on the body, especially under the belly and the back of the neck. The African cheetah has a light brown to golden brown fur color that is thicker than the Asiatic ones. The spots are more pronounced on the face and are more densely distributed on the body compared to Asiatic cheetahs.
African cheetah Asiatic cheetah
- Asiatic Cheetahs are only found in a small region between Iran and Pakistan. Asiatic cheetahs once roamed the whole expanse of the central Asian continent from India to Afghanistan and Pakistan, but with their numbers reduced, it is hard for them to be sighted outside Iran. On the other hand, The African cheetah is spread out across Africa from Northwest Africa, East Africa, and Southern Africa. With a bigger territory, the African cheetahs have the highest populations compared to their Asiatic counterparts.
- Asiatic cheetah has been listed as Critically Endangered on the IUCN Red while African cheetahs are listed as Vulnerable on the IUCN Red List.
Most of the reasons for the cheetah’s endangerment can be grouped into three overarching categories:
- human-wildlife conflict,
- loss of habitat and loss of prey,
- poaching and illegal wildlife trafficking, with cubs being taken from the Horn of Africa and smuggled into the exotic pet trade, primarily in the Gulf States.
3. GRAVITATIONAL WAVES
TAGS: GS 3: SCIENCE AND TECHNOLOGY
CONTEXT: Since time immemorial, humans have looked up at the universe and pondered its secrets. In the past few centuries, many of these secrets have started to unravel. One such mystery we began to pry apart very recently is the gravitational wave. Gravitational waves are ripples in space-time produced by some of the most intense phenomena in our universe.
EXPLANATION:
- A century ago, Albert Einstein hypothesized the existence of gravitational waves, small ripples in space-time that dash across the universe at the speed of light.
- But scientists have been able to find only indirect evidence of their existence.
- Recently, a news conference called by the U.S. National Science Foundation, researchers announced at long last direct observations of the elusive waves.
- The discovery would represent a scientific landmark, opening the door to an entirely new way to observe the cosmos and unlock secrets about the early universe and mysterious objects like black holes and neutron stars.
What are gravitational waves?
- Gravitational waves are small ripples in space-time that are believed to travel across the universe at the speed of light.
- These waves contain information about the events that emitted them, so studying them can give scientists a glimpse of distant cosmic affairs.
What does Einstein say about gravity?
- In 1915, Albert Einstein’s theory of relativity predicted the existence of gravitational waves.
- According to this theory, celestial objects such as black holes and neutron stars could send gravitational energy thrumming through the fabric of space-time in every direction, moving off at the speed of light.
- While Sir Isaac Newton visualised gravitational force as a pulling force between objects, Albert Einstein opined it to be a pushing force due to the curvature of four dimensional spacetime fabric.
How are these waves detected?
- Scientists have been trying to detect them using two large laser instruments in the United States, known together as the Laser Interferometer Gravitational-Wave Observatory (LIGO), as well as another in Italy.
- The twin LIGO installations are located roughly 3,000 km apart in Livingston, Louisiana, and Hanford, Washington. Having two detectors is a way to sift out terrestrial rumblings, such as traffic and earthquakes, from the faint ripples of space itself.
- The LIGO work is funded by the National Science Foundation, an independent agency of the U.S. government.
What is Laser Interferometer Gravitational-wave Observatories (LIGO)?
- The Laser Interferometer Gravitational-Wave Observatory is a large-scale physics experiment aiming to directly detect gravitational waves.
- They directly observed gravitational waves for the first time in 2015, proving Einstein’s theory.
- LIGO operates two gravitational wave observatories in unison: the LIGO Livingston Observatory in Livingston, Louisiana, and the LIGO Hanford Observatory, on the DOE Hanford Site, located near Richland, Washington.
- These sites are separated by 3,002 kilometers. Since gravitational waves are expected to travel at the speed of light, this distance corresponds to a difference in gravitational wave arrival times of up to ten milliseconds. A third LIGO will be built in India this decade.
Why is the study important?
- Discovery of gravitational waves would represent a scientific landmark, opening the door to an entirely new way to observe the cosmos and unlock secrets about the early universe and mysterious objects like black holes and neutron stars.
4. GENETICALLY MODIFIED CROPS
TAG: GS 3: ENVIRONMENT; GS 3: SCIENCE AND TECHNOLOGY
CONTEXT: Genetically modified crops remains controversial, especially in Europe, but for some experts it is the best science-based method for a sustainable global food system amidst biodiversity loss and a rising population. According to the online scientific publication Our World in Data, agriculture is responsible for a quarter of the carbon emissions in the atmosphere and the vast majority of world’s biodiversity losses.
EXPLANATION:
Genetically modified organisms (GMOs)
- Genetically modified organisms (GMOs) can be defined as organisms i.e. plants, animals or microorganisms in which the genetic material (DNA) has been altered in a way that does not occur naturally by mating and/or natural recombination.
- The technology is often called “modern biotechnology” or “gene technology”, sometimes also “recombinant DNA technology” or “genetic engineering”.
- It allows selected individual genes to be transferred from one organism into another, also between nonrelated species.
- GMOs were first introduced in the US in 1994, with modified tomato plants that ripened more slowly to prolong their shelf life. Since then, a wide range of crops, such as soybeans, wheat and rice have been approved for agricultural use, along with GM bacteria grown to produce large amounts of protein.
- Scientists in India have also developed strains of Sub-1 rice, which are much more resistant to flooding. Flooding is a major issue in rice-growing regions of northern India and Bangladesh, set to become worse as the climate crises develops, and now 6 million farmers in the region are using Sub-1 rice to safeguard their crops against inundation.
- Golden rice, on the other hand, is a GM strain modified to contain vitamin A, designed to combat the shortage of dietary vitamin A in parts of Asia and Africa.
GM Crops:
- Crops produced from or using GM organisms are often referred to as GM crops.
- Genetically modified crops can improve yield, build resistances to pests, frost or drought, or add nutrients.
- Crops can also be modified to reduce carbon emissions and boost the sustainability of food production.
- While widespread, GM crop productionuses only about 10% of the land non-GM crop production uses.
Benefits:
- GM crops are developed and marketed because there is some perceived advantage either to the producer or consumer of these foods. This is meant to translate into a product with a lower price, greater benefit (in terms of durability or nutritional value) or both.
- One of the objectives for developing plants based on GM organisms is to improve crop protection. The GM crops currently on the market are mainly aimed at an increased level of crop protection through the introduction of resistance against plant diseases caused by insects or viruses or through increased tolerance towards herbicides.
- Resistance against insects is achieved by incorporating into the food plant the gene for toxin production from the bacterium Bacillus thuringiensis (Bt). This toxin is currently used as a conventional insecticide in agriculture and is safe for human consumption.
- Herbicide tolerance is achieved through the introduction of a gene from a bacterium conveying resistance to some herbicides. In situations where weed pressure is high, the use of such crops has resulted in a reduction in the quantity of the herbicides used.
What are the main issues of concern for human health?
- Allergenicity: As a matter of principle, the transfer of genes from commonly allergenic organisms to non-allergic organisms is discouraged unless it can be demonstrated that the protein product of the transferred gene is not allergenic.
- Gene transfer: Gene transfer from GM foods to cells of the body or to bacteria in the gastrointestinal tract would cause concern if the transferred genetic material adversely affects human health.
- Outcrossing: The migration of genes from GM plants into conventional crops or related species in the wild (referred to as “outcrossing”), as well as the mixing of crops derived from conventional seeds with GM crops, may have an indirect effect on food safety and food security.
5. IRON FORTIFICATION: HEALTH RISKS OF EXCESSIVE IRON INTAKE
TAG: PRELIMS PERSPECTIVE
CONTEXT: Iron is an essential mineral required for many bodily functions, including the formation of hemoglobin, but can be harmful when taken in excess. The net effect of iron provision through fortification on haemoglobin formation is likely to be lower than thought.
EXPLANATION:
- It is used for the treatment of iron deficiency or anemia.
- Typically, a chosen food staple like wheat or rice or even salt is fortified to provide up to two thirds (10 mg/day) of the iron requirement of adult women, and almost the entire daily requirement of men.
How excess consumption occurs:
- Excess consumption of iron can occur if one habitually consumes a balanced quality diet to begin with or exceeds limits for consumption of the fortified food as can occur with staples like rice or wheat or if two fortified foods are simultaneously consumed.
- When combined with additional iron supplemental interventions like weekly iron folic acid supplements (such as in the National Iron Plus Initiative programme), this can lead to an excess of iron intake for women. There is a defined level of iron intake beyond which the risk of adverse events begins to increase. This is called the ‘tolerable upper limit’ of intake, and is set at 40 mg/day.
- Once iron is absorbed, it is thought that its excretion is steady and very small, except when bleeding takes place, as with menstrual bleeding. Thus, women can ‘excrete’ iron from the body, but men cannot, unless they have some form of pathological or abnormal bleeding. This makes men particularly vulnerable to excess iron intake.
Negative consequences of excess iron:
- Unabsorbed iron can lead to inflammation in the gastrointestinal lining and disrupt the colonic microbiota with long term consequences.
- This irritation of the lining may present itself clinically as abdominal cramps, constipation, or diarrhoea.
- The irritation of mucosa can also lead to gastrointestinal blood loss.
- An excess of iron in the gastrointestinal tract can impair absorption of other minerals such as zinc and copper, which are also essential for the body and lead to other deficiencies.
- Excess iron has been closely linked to many chronic comorbidities like diabetes.
It can be especially deleterious for populations who have iron overload states like patients with thalassemia and other hemolytic anemias, hemochromatosis, and chronic liver disease, which have impaired iron excretion mechanisms.
