Changes in ocean ‘conveyor belt’ leading to abrupt climate changes

Simplified diagram of the Atlantic Meridional Overturning Circulation
Simplified diagram of the Atlantic Meridional Overturning Circulation.Credit: Muschitiello et al., Nature Communications, 2019

We are all aware of global warming due to which we experience a lot of changes in the climate. Recently a team of experts found out that there are changes that are happening due to this global warming in the ocean.

Let us now understand as to what are the changes happening in the ocean. In the Atlantic Ocean there lies a giant “conveyor belt” that carries warm water from the tropics into the North Atlantic, where they cool down and sink southwards into the ocean. This circulation pattern is a very important player in the global climate change since it regulates the weather patterns in the Arctic, Europe and across the world.

Today, we have strong evidence that the conveyor belt is slowing down. The scientists are scared that this would cause a dangerous situation to occur like causing climatic changes in Europe and warming the waters of the East Coast of the United States which in return could harm the horticulture.

According to a study done by collaboration between scientist at the Columbia’s Lamont-Doherty Earth Observatory and the Norwegian Research Centreit is believed that if this slowing process continues and there is no measure taken in order to stop it, the entire system would become weak and the effects would be worst.

The above study precisely determines the time lags between past changes to the ocean conveyor belt and major climate changes.

Thermohaline Circulation
This map shows the pattern of thermohaline circulation also known as “meridional overturning circulation”. This collection of currents is responsible for the large-scale exchange of water masses in the ocean, including providing oxygen to the deep ocean. The entire circulation pattern takes ~2000 years. (Source: Nasa Earth Observatory)

The team of scientists studied the AMOC (Atlantic Meridional Overturning Circulation) which is a key section in the ocean current pattern. They zeroed in on a section where water sinks from the surface to the bottom of the North Atlantic and they confirmed that the AMOC started weakening about 400 years before a major cold snap 13,000 years ago and began strengthening again about 400 years before abrupt warming 11,000 years ago.

Francesco Muschitiello from the University of Cambridge and the lead author said, “Our reconstructions indicate that there are clear climate precursors provided by the ocean state—like warning signs, so to speak.

In order to understand whether these changes in the ocean conveyor belt occurred before or after the abrupt climatic shifts that punctuated the last deglaciation in the Northern Hemisphere, the scientist pieced together the data from a sediment core drilled from the bottom of the Norwegian Sea, a lake sediment core from southern Scandinavia, and ice cores from Greenland.

Usually, Carbon-14 is used in order to determine the age of that particular fossil but in oceans, it is not possible to determine as Carbon-14 is formed in the atmosphere and it takes time for it to reach the oceans. That is why Carbon is measured in the nearby lake sediment core and they found out the age of each sediment core.

Now they compared the real age of the marine sediments to the age they were reading from Carbon-14 measurements. Indifference in them gave an estimate of how long it took for Carbon-14 to reach the ocean which means it revealed that how quickly the water was sinking in this area in a process called “deep water formulation” which is essential to keep the AMOC going.

Detailed view of synchronized CO2, climate and ocean circulation records during the Younger Dryas stadial
Detailed view of synchronized CO2, climate and ocean circulation records during the Younger Dryas stadial. Credit: Muschitiello et al., Nature Communications, 2019

The final piece of the puzzle was to analyze ice cores from Greenland, to study changes in temperature and climate over the same time period. Measurements of Beryllium-10 in the ice cores helped the authors precisely link the ice cores to the Carbon-14 records, putting both sets of data on the same timeline. Now they could finally compare the order of events between ocean circulation changes and climatic shifts.

Comparing the data from the three cores revealed that the AMOC weakened in the time leading up to the planet’s last major cold snap, called the Younger Dryas, around 13,000 years ago. The ocean circulation began slowing down about 400 years before the cold snap, but once the climate started changing, temperatures over Greenland plunged quickly by about 6 degrees.

Keeping all that aside, let us stop polluting and let us take preventive measures so as to prevent this slow down of the above-mentioned conveyor belt and to save humanity from its disastrous effect.

Published Research:


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