Oldest Water

World’s Oldest Water Trapped in a “Shadow Zone” Deep in the Ocean

The age of any ocean water is calculated on the basis of its re-circulation process. Typically it takes few days to few years, to come in contact with the atmosphere. But deep in the North Pacific Ocean, there is a place that has remained trapped in a “shadow zone” 2 km below the sea surface for near about 2000 years. A group of scientists from the ARC Centre of Excellence for Climate System Science at the University of New South Wales (UNSW), Australia carried out a study to find out the processes that kept the water from circulating back to the surface. The world’s oldest water has certainly drawn some serious attention from the science enthusiasts all over the world.

Oldest Water
Satellite imagery of part of the North Pacific Ocean. (Credit: NOAA)

Regarding the “shadow zone,” Casimir de Lavergne one of the lead oceanographers from the University of New South Wales in Australia stated, “Carbon-14 dating had already told us the most ancient water lies in the deep North Pacific. But until now we had struggled to understand why the very oldest waters huddle around the depth of 2km in this ocean.” According to their new analysis, the deep water movement is called as abyssal overturning circulation. Due to the geometry of the seafloor, it prevents the deep and dense ocean waters from circulating to the surface for a long time.

Oldest Water
(Credit: Fabien Roquet and Casimir de Lavergne | Science Alert)

The seabed topography forbids the water to reach the ocean surface, which leads to low oxygen concentrations in the shadow zone compared to waters sitting higher in the sea. But this does not mean that it can not support any life. “Shadow zones” are very common in Indian and Pacific Oceans whereas the Atlantic Ocean does not have such shadow zones. The influx of cold water from the north prevents to form any such zones.

Oldest Water
This animation shows the path of the global conveyer belt. The blue arrows indicate the path of deep, cold, dense water currents. The red arrows indicate the path of warmer, less dense surface waters. It is estimated that it can take 1,000 years for a “parcel” of water to complete the journey along the global conveyor belt. (Credit: NOAA)

While investigating the reason behind the trapping, the researchers also explored the water to find out its effect on the ocean system as a whole. They found out that the millennia-old ocean water traps nutrients and carbon which have a direct impact on the capacity of the ocean to influence climate over time. Oceanographer Ryan Holmes from the ARC Centre of Excellence for Climate System Science said, “So, while the research may have answered one question about deep ocean water, it has also opened doors to answer more questions that relate to the future impacts of climate change and the ecology of our major oceans”.

Source: ARC CECSS, The Sydney Morning Herald, Nature, Science Alert

Sayan is a theoretical physicist from Plasma Science discipline. He is a front-end developer with an eye for details and a passion for perfection. He enjoys writing popular science articles and taking part in discussions.