The focus of recent climate research zeroes in on Antarctica, with observations indicating that the continent’s deep ocean currents are slowing down earlier than anticipated. This phenomenon could potentially disrupt the overarching overturning circulation, which is central to maintaining global climatic stability. Over the past three decades, significant changes have been noted in the Antarctic deep ocean, including a decline in oxygen levels — an alarming indication of the possible environmental consequences to come.
Overturning Circulation: The Global Temperature Regulator
Overturning circulation refers to the worldwide network of ocean currents that work to distribute heat, carbon, and nutrients throughout the world’s seas. In Antarctica, this involves the sinking of dense, oxygen-rich water from the surface, its spread across the seabed, and eventual rise in other areas.
The circulation process begins in the polar regions, where frigid air masses cause surface water to cool. This cooling instigates the formation of sea ice, which extracts freshwater from the surrounding seawater, thereby increasing the salinity and density of the remaining water. As the water becomes denser, it sinks to lower layers and forms what is known as bottom water. This descent is the force behind overturning circulation, as the dense water travels towards the equator while warmer surface water moves polewards.
As it travels, the deep water mixes with other water masses, facilitating heat, carbon, and nutrient exchange. This modified water eventually re-surfaces, completing the overturning circulation.
The Importance of Overturning Circulation in Climate Stability
Crucial to maintaining Earth’s climate stability, overturning circulation acts as the planet’s temperature regulator. By transporting heat, carbon, and nutrients, it has a widespread influence on the global climate system. Moreover, it ensures the oxygen supply to the deep ocean, which is vital for sustaining marine life.
The Consequences of Slowing Overturning Circulation
The observed slowdown in Antarctica’s deep ocean currents rings alarm bells for climate stability. A diminished flow of bottom water leads to a decreased oxygen supply in the deep ocean, which affects oxygen-dependent marine organisms. Lower oxygen levels can induce behavioural changes, migrations, and food chain disruptions.
Moreover, the slowdown amplifies global warming as the ocean’s ability to store carbon dioxide and heat decreases, thereby intensifying the greenhouse effect.
The Impact of Melting Antarctic Ice on Overturning Circulation
Melting Antarctic ice further complicates the matter by disrupting the formation of Antarctic bottom water. This makes surface waters fresher and less dense, hindering their sinking ability. Consequently, the overturning circulation weakens, diminishing the oxygen supply to the deep ocean.
The replacement of bottom water with warmer, oxygen-deprived waters also exacerbates the decline in oxygen levels. Besides, the melted ice contributes to sea-level rise due to thermal expansion, since warmer water occupies more volume.
Key Insights on Antarctica
Antarctica, Earth’s southernmost continent, is uninhabited except for the staff at about 40 permanent research stations. India, among a few other countries, maintains two such research stations — ‘Maitri’ and ‘Bharati’. The Indian Antarctic Programme operates under the National Centre for Antarctic and Ocean Research, Ministry of Earth Sciences, having launched 41 scientific expeditions to date.
Antarctica, covering 14,000,000 square kilometres, is the fifth-largest continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere. India officially acceded to the Antarctic Treaty System in August 1983, marking its dedication to polar research.
