Date: 03/04/2023
Relevance: GS-3: Climate Change, Global Warming, Ocean Circulation and its effects.
Key Phrases: Atlantic Meridional Overturning Circulation (AMOC), Climate Change, IPCC, Developed Countries, Mitigation Efforts, Global Warming, Marine Productivity, UNEP, Climate Challenge.
Context:
- According to a study published recently in the journal Nature, deep
ocean water flows from the Antarctic could decline by 40% by 2050.
- Rapidly melting Antarctic ice is dramatically slowing down the flow of water through the world's oceans, and could have a disastrous impact on the global climate, the marine food chain and even the stability of ice shelves.
Key Highlights:
- Led by scientists from the University of New South Wales and published in the journal Nature, the peer-reviewed study modeled the impact of melting Antarctic ice on deep ocean currents that work to flush nutrients from the seafloor to fish near the surface.
- Scientists relied on around 35 million computing hours over two years to crank through a variety of models and simulations up to the middle of this century, finding deepwater circulation in the Antarctic could weaken at twice the rate of decline in the North Atlantic.
- The effect of meltwater on global ocean circulation has not yet been included in the complex models used by the IPCC to describe future climate change scenarios, but it is going to be considerable.
Key Findings:
- Three years of computer modeling found the Antarctic overturning
circulation – also known as abyssal ocean overturning – is on track to slow
40% by 2050 if the world continues to burn fossil fuels and produce high
levels of planet-heating pollution.
- A slowdown is expected to speed up ice melt and potentially end an ocean system that has helped sustain life for thousands of years.
- In the past, these overturning circulations changed over the
course of 1,000 years or so, but now these changes are occuring
within a few decades.
- So it is pretty dramatic and challenging.
- The circulation of deep ocean water is considered vital for the health of the sea – and plays an important role in sequestering carbon absorbed from the atmosphere.
- According to the report, while a slowdown of the AMOC would mean the deep Atlantic Ocean would get colder, the slower circulation of dense water in the Antarctic means the deepest waters of the Southern Ocean will warm up.
- In certain areas, mostly south of Australia in the Southern Ocean and in
the tropics, this nutrient-rich cold water moves toward the surface in a
process called upwelling, distributing the nutrients to higher layers of
the ocean.
- However, the study found that as global temperatures warm, melting sea ice “freshens” the water around Antarctica, diluting its saltiness and raising its temperature, meaning it’s less dense and doesn’t sink to the bottom as efficiently as it once did.
- Nutrients exported from the Southern Ocean in other current systems support about three quarters of global phytoplankton production – the base of the food chain.
- The study's findings also suggest the ocean would not be able to absorb as much carbon dioxide as its upper layers become more stratified, leaving more CO2 in the atmosphere.
- Sinking of dense water near Antarctica will decline by 40% by 2050, sometime between 2050 and 2100, impacts of this will start to be seen on surface productivity.
Atlantic Meridional Overturning Circulation (AMOC)
- About:
- The Atlantic Meridional Overturning Circulation (AMOC) is a major ocean current system that transports warm surface waters from the tropics toward the northern Atlantic and colder deep waters that are part of the thermohaline circulation, southward.
- It is driven by the movement of denser water towards the sea floor, helps deliver heat, carbon, oxygen and vital nutrients around the globe.
- One of the main ways the ocean circulates heat, salt, carbon, and nutrients throughout the world’s oceans is through overturning circulation.
- Significance:
- It helps to disperse heat and energy throughout the earth.
- Because of it, the climate in Western Europe is less severe even during the winter (Gulf Stream, North Atlantic Drift).
- By absorbing and storing carbon from the atmosphere, it serves as a carbon sink.
- The distribution of heat to the polar regions is largely
dependent on thermohaline circulation.
- As a result, it impacts how quickly sea ice forms at the poles, which in turn affects other components of the climate system such as the albedo, and thus solar heating, at high latitudes.
- Consequences of a slowing down of AMOC:
- It will increase the regional sea level along the northeast coast of North America.
- It will cause more storms in Northern Europe.
- It will cause a decrease in South Asian summer rainfall.
- It will further decline in marine productivity in the North Atlantic.
Conclusion:
- Sea life in waters worldwide rely on nutrients brought back up to the surface, and that the Antarctic overturning is a key component of that upwelling of nutrients.
Source: The Hindu
Mains Question:
Q. What is Atlantic Meridional Overturning Circulation (AMOC)? Also discuss the significance of AMOC on global climate. (150 Words).
