According to studies, the oceans are stratifying faster than many previous studies. This is largely due to the rising temperatures and the freezing layers of the oceans, which lead to carbon storage, which can affect ecosystems around the world.
For now, it is clear that the planet is holding on to more heat, thanks to a layer of man-made greenhouse gas emissions. But the effect of ocean stratification is not one of the noticeable consequences. To understand how climate change divides oceans into layers, scientists used a combination of models and data gathered from networks of self-propelled buoys that travel across the ocean. These buoys are equipped with sensors that record the ocean’s temperature, salinity, density and other variables.
The data set allowed the team to analyze the entire period from 1960 to 2018. They found that the water in some parts of the ocean floor had become less dense. This is predictable because warmer water will be less dense than cold water. But the changes are not uniform.
The heat at the ocean’s surface takes longer to propagate to the deeper aquifers, meaning that the upper layers of the ocean are getting hotter than the lower layers. That decomposition by temperature leads to greater stratification. According to the study, temperature changes make ocean stratification more extreme in more than 90% of the area they observed.
Salinity also plays a role, as fresh water is less dense than salt water. This is a major problem in places near melting ice sheets like the North Atlantic off the Greenland coast.
Although the Arctic data are more sparse, the changes in salinity and temperature observed there are leading to some of the harshest rates of stratification on the planet. But in some places, the ocean becomes more and more salty due to increased evaporation. The findings show that in the Atlantic, the stratification due to temperature is nearly 1.6 times higher than extreme due to increasing salinity, especially in the tropical Atlantic.
The findings show a significant, approximately 5.3% increase in ocean stratification globally during the study period. The time in the new study is longer than the most recent report by the Intergovernmental Panel on Oceanic Climate Change published last September.
Last year’s IPCC report found stratification is one of the factors that lead to lower productivity of the world’s most important marine ecosystems for humans, such as California’s Humboldt Current.
This is because the warm water layer on the top of the ocean acts as a lid, preventing nutrient-rich water at the bottom from rising to the surface. Without it, organisms at the bottom of the food chain decrease and the impact is pervasive throughout the ecosystem. Dead zones in the ocean are also attached to increasingly warmer ocean surfaces and indirectly degrading marine biodiversity.
Stratified oceans also absorb less CO2, which is not quite as good as humans are still continuously releasing CO2 into the atmosphere. That could create a loop when human carbon pollution is still very much in the atmosphere, leading to warmer oceans and less carbon absorption.
So, basically, you can imagine the ocean as a cake and people have to find some way to turn off the oven as soon as possible.
The new study is published in the new journal Nature Climate Change.