As the Pacific Ocean warms, the 'age' of the water within the ocean is also changing. Scientists from the University of California, San Diego, used a model to study the changes that will occur over the next hundred years. The research showed that in some parts of the Pacific Ocean, new water can become old, while in other areas, old water can become new.
The main reason for this phenomenon is the decrease in activity between different layers of water following global warming. These changes are particularly observed in the layer ranging from 200 to 1000 meters deep, known as the thermocline. The thermocline is the boundary between the warm upper layer and the colder waters below. As the ocean heats up, these layers stop mixing as easily, which slows down the vertical movement of water. This leads to changes in water age and oxygen levels in different locations.
'Water age' refers not to the number of years the water has existed, but to the period during which it has not reached the sea surface. When water is at the surface, it becomes saturated with oxygen from the air. Then, as it sinks, it is used by marine organisms and bacteria to consume this oxygen. Therefore, water that remains in the depths for a long time is considered 'old' due to reduced oxygen content, whereas recently sunk water is considered 'new' and is usually rich in oxygen.
Since warm water is lighter than cold water, there are distinct layers in the ocean: warm water on top and cold water below. Rising temperatures intensify the gap between these layers. This reduces the mixing of water vertically in the ocean. Scientists recorded this slowing of water movement in their model.
In one area of the North Pacific Ocean, new water coming from above reaches the thermocline, but due to rising temperatures, it may penetrate less deeply. As a result, this water may remain in the ocean longer, meaning the new water gradually becomes 'old.' This could also lead to a decrease in oxygen levels in this area. According to the study, this may affect marine life that requires oxygen to survive.
The situation in the tropical part of the Pacific Ocean may develop in the opposite way. There, water rising from below is initially old and low in oxygen. Warming may slow down the movement of water from the depths to the surface. Consequently, old water will reach the upper layer less frequently, which could lead to a decrease in the average age of the water in the upper layer.
Thus, in one part of the Pacific Ocean, water may age, while in another part, old water may become relatively new.
Scientists also noted the role of the Southern Ocean, which surrounds Antarctica. Temperature rise in this region can alter large-scale water movement, which directly affects the Pacific Ocean. This is why scientists view this as an influence of warming in one part of the ocean on another.
Warm water may contain less oxygen. Furthermore, the slowing of water movement changes how oxygen is delivered to greater depths. Although this study did not examine all consequences for marine organisms, scientists note that in areas with low oxygen content, no sharp increase in oxygen deficiency is expected in the next hundred years.
However, in the northern part of the Pacific Ocean, the change in water age and oxygen levels may have a more significant impact on marine life, as oxygen is already deficient there.
In this study, scientists used a simple ocean model to predict changes over the next approximately 100 years. Future research should include the analysis of ocean winds and changes in their patterns. This study makes it clear that the impact of climate change will not be uniform across the entire Pacific Ocean. In different parts of the ocean, water movement, its 'age,' and oxygen levels may change differently, potentially affecting the marine environment in the future.