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Secrets of Iceland and Scotland: How were the deep waters of the North Atlantic formed?
In the deep sea of the North Atlantic, there exists a mysterious and important water mass called North Atlantic Deep Water (NADW). The formation of this deep water mass has a crucial impact on global ocean circulation and climate change. This article will take you in-depth exploration of the origin, formation process and role of the North Atlantic deep water in the global climate system.
The formation process of deep water in the North Atlantic
NADW is a deep water mass formed in the North Atlantic Ocean by cooling, highly saline water. It is formed primarily through the global ocean's thermohaline cycle, also known as the longitude overturning cycle, in which heat flows from warm surface waters in the Southern Hemisphere into the North Atlantic. As the water flows northward, the water's salinity increases.
When this water reaches the North Atlantic, the cold temperatures and high salinity cause it to become denser and eventually sink to the bottom of the ocean.
Characteristics of NADW include high salinity, high oxygen content and nutrient minima, and the water layer in which it is located typically has a temperature of 2-4°C, a salinity range of 34.9 to 35.0 psu, and a depth of 1500 m to 4000 m. meters.
The composition and origin of water masses
The development of the NADW is a complex process originating from deep convection and water overflow from the Greenland-Iceland-Scotland ridge. Major water masses in the North Atlantic, such as Labrador Sea (LSW), are affected by convection and can deepen to 2,000 meters in winter.
Under the influence of the positive North Atlantic Oscillation (NAO), strong intercambio of rain and wind creates conditions conducive to the sinking of denser water.
In addition, Iceland-Scotland overflow water (ISOW) and Denmark Strait overflow water (DSOW) are the two main sources that constitute NADW. These water masses originate from the mixing of Greenland and deep Arctic Ocean waters, and further increase in density after prolonged periods of convection and gravity settling.
Dispersion pathways of water masses
NADW flows along the Deep Western Boundary (DWBC), and its flow path can be traced by its high oxygen content, high CFC concentration and density. The NADW in the upper layer mainly comes from the Upper Labrador Sea Water (ULSW). These water masses will flow from the Labrador Sea to the south and mix with the DWBC at the same time.
Some ULSW will mix with other water masses in the tropical Atlantic region, while others will remain in the DWBC.
The lower NADW is composed of DSOW and ISOW, which flow around the Imilgen Basin and expand southward at a relatively low speed into the deep area of the Atlantic Ocean.
Impact of change
The formation process of deep water in the North Atlantic is sometimes affected by climate change, and there have been many instances in history where NADW formation has decreased. These phenomena may be related to a decrease in the intensity of the North Atlantic Drift, which in turn affects the climate of northwest Europe.
Now, scientists are worried about the impact of global warming on NADW, believing that it may once again change the ocean's thermohaline cycle.
Our understanding of the deep waters of the North Atlantic is incomplete, and how these deep waters will affect the functioning of the climate system in the future is still unknown, especially as the environment changes. Perhaps, we can think about: How can we prepare for possible changes in ocean circulation to ensure the stability and sustainability of the ecosystem?
