Atlantification UPSC NOTE

Atlantification

Atlantification is the increasing influence of Atlantic water in the Arctic.
Warmer and saltier Atlantic water is extending its reach northward into the Arctic Ocean.
The Arctic Ocean is becoming warmer and saltier and sea-ice is disappearing as a result.
This change in the Arctic climate is most prominent in the Barents Sea, a shallow shelf sea north of Scandinavia, where sea-ice is disappearing faster than in any other Arctic region, impacting the local and global ecosystem.

Process of Atlantification

The increasing influence of Atlantic water flowing into the Arctic Ocean and the loss of stratification causes the warm Atlantic water to mix with the fresh water at the surface.
The halocline weakens and therefore heat from the Atlantic water reaches the surface.
This warming of the surface water causes a retreat in sea-ice in winter and a total absence of sea-ice in summer.
The loss of winter sea-ice means that in summer, the colder layer of freshwater at the surface is less replenished by melting ice, lessening the temperature difference between the layers.

Process of Atlantification

Also, a lack of sea-ice increases the influence of wind on the sea surface, mixing the layers further.
Model predictions do not show an upward trend in volume transport into the Arctic from the North Atlantic nor an increase in the temperature of the inflowing water.
It leading some to conclude that the Atlantification of the Arctic is not caused by a process in the Atlantic Ocean but rather by atmospheric forcing in the Arctic region, amplified by sea-ice loss.

However observations show a regime shift from winter sea ice cover to open water in the southern Barents Sea in response to the warming of the inflowing Atlantic water.
Observations also reveal the increasing influence of Atlantic water heat further to the east, in the eastern Eurasian Basin, where in recent years the heat flux from the Atlantic water towards the surface has overtaken the atmospheric contribution in this region.
Furthermore, an observed weakening of the halocline over this period coincided increasing wind driven upper ocean currents, pointing to increased mixing.

Consequences

At the moment, the largest part of inflowing heat from the Atlantic Ocean is lost to the atmosphere within the Barents Sea.
It is expected though, that the temperature in the Barents Sea will increase due to changes in the interaction with the atmosphere.
As a result, the water flowing out from the Barents Sea will warm significantly from -0.2∘C to 2.2∘C in 2080.
This shows that warm Atlantic water will penetrate further into the Arctic Ocean, ultimately extending throughout the Eurasian basin, leading to reduction in sea-ice thickness in this region.

Due to the warming of Barents Sea, phytoplankton blooms are moving further into the Eurasian Basin each year.
Typical species have moved 5 degrees further North compared to 1989.
Also, fish communities are moving Northward at the pace of the local climate change, a process called borealization.
Some predators that reach areas previously not warm enough change the ecological systems of the Arctic.
As a result, Arctic shelf fish are being expelled and retract Northwards as well.

For some species, depth might limit their options and this will induce changes in the biodiversity of the Arctic Ocean.
This change in marine ecosystem also influences the bird and mammal species living in the Arctic region.
Sea birds, seals and whales depend directly on the fish populations.
Land mammals like polar bears live on seals and are also strongly dependant on the sea-ice to live on.

There are growing concerns that the Arctic climate might be moving to a so-called tipping point, meaning that if a critical point is reached, the system will settle around a different equilibrium state.
In the Arctic this different state could be one with much less or no sea-ice.

Why it is in news?

Arctic Dipole

The Arctic dipole anomaly is a pressure pattern characterized by high pressure on the arctic regions of North America and low pressure on those of Eurasia.
This pattern sometimes replaces the Arctic oscillation and the North Atlantic oscillation.
It was observed for the first time in the first decade of 2000s and is perhaps linked to recent climate change.

The Arctic dipole lets more southern winds into the Arctic Ocean resulting in more ice melting.
The Arctic dipole has also been linked to changes in arctic circulation patterns that cause drier winters in Northern Europe, but much wetter winters in Southern Europe and colder winters in East Asia, Europe and the eastern half of North America.

What was the findings of the recent study?

Analysis shows that the Arctic dipole alternates in an approximately 15-year cycle and that the system is probably at the end of the present regime.

In the Arctic dipole’s present “positive” regime, high pressure is centered over the Canadian sector of the Arctic and produces clockwise winds.
Low pressure is centered over the Siberian Arctic and features counterclockwise winds.
This wind pattern drives upper ocean currents, with year-round effects on:

Water exchanges between the Nordic seas and the Arctic Ocean are critically important for the state of the Arctic climate system and sea ice decline is “a true indicator of climate change.”

Ocean responses to wind pattern:

Decreased flow from the Atlantic Ocean into the Arctic Ocean through the Fram Strait east of Greenland, along with increased Atlantic flow into the Barents Sea, located north of Norway and western Russia.
These alternating changes in the Fram Strait and the Barents Sea are referred to as a “switchgear mechanism” caused by the Arctic dipole regimes.

This mechanism can lead to potentially more suitable living conditions for sub-Arctic boreal species near the eastern part of the Eurasian Basin, relative to its western part.
Counterclockwise winds from the low-pressure region under the current positive Arctic dipole regime drive freshwater from Siberian rivers into the Canadian sector of the Arctic Ocean.
This westward movement of freshwater from 2007 to 2021 helped slow the overall loss of sea ice in the Arctic compared to 1992 through 2006.
The freshwater layer’s depth increased, making it too thick and stable to mix with the heavier saltwater below.

The thick layer of freshwater prevents the warmer saltwater from melting sea ice from the bottom.

Fram Strait

The Fram Strait is the passage between Greenland and Svalbard, centered on the prime meridian.
The Greenland and Norwegian Seas lie south of Fram Strait, while the Nansen Basin of the Arctic Ocean lies to the north.
Fram Strait is noted for being the only deep connection between the Arctic Ocean and the World Oceans.

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