According to a study released Wednesday, climate change has brought about significant changes in ocean stability faster than previously thought, and has raised alarms about its role as a global thermostat and the marine life it supports.
The research published in the journal Nature examined 50 years of data and tracked how surface waters “decouple” from the deepest ocean.
Climate change has altered the mixing of the oceans, a process that helps store most of the world’s excess heat and a significant proportion of CO2.
Surface water is warmer and therefore less dense than bottom water, a contrast that intensifies with climate change.
Global warming also causes large amounts of fresh water to be produced in the sea due to the melting of ice sheets and glaciers, reducing the salinity of the top layer and further reducing its density.
This growing contrast between the density of the oceanic layers makes the mixture harder, so that oxygen, heat, and carbon are less able to penetrate into the deep seas.
“Similar to a layer of water on oil, surface water in contact with the atmosphere mixes less efficiently with the underlying ocean,” said lead author Jean-Baptiste Sallee of the University of the Sorbonne and the CNRS national scientific research center in France.
He said that while scientists were aware that this process was underway, “here we show that this change has occurred at a much faster rate than previously thought: more than six times faster.”
The report used global temperature and salinity observations obtained between 1970 and 2018, including those of electronically monitored marine mammals, with a focus on the summer months, which have more data.
He said the barrier layer separating the ocean surface and the deep layers had been strengthened worldwide, as measured by density contrast, at a much greater rate than previously thought.
The researchers also found that, contrary to their expectations, winds strengthened by climate change had also acted to deepen the ocean’s surface layer by five to ten meters per decade over the past half century.
A significant number of marine animals live in this surface layer, with a food web that depends on phytoplankton.
But as the winds increase, the phytoplankton gets deeper, away from the light that helps them grow, which can affect the wider food web.
These “are not small changes that only some experts are interested in,” Sallee told AFP.
“They represent a fundamental change in the underlying structure of our oceans. Much more pronounced than we previously thought.”
Deep and worrying
The oceans play a crucial role in mitigating the effects of climate change by absorbing about a quarter of man-made CO2 and absorbing more than 90% of the heat generated by greenhouse gases, according to the Intergovernmental Group for Climate Change (IPCC).
“But as it stabilizes, the role of the ocean in dampening climate change becomes more difficult as it becomes more difficult for the ocean to absorb these large amounts of heat and carbon,” Sallee said.
Scientists are sounding more and more alarms about the possible implications of warming in our oceans.
In 2019, a research was published in the US Proceedings of the National Academy of Sciences he calculated that climate change would empty the ocean of nearly one-fifth of all living creatures, measured by mass, by the end of the century.
Climate scientist Michael Mann warned in September that the findings of a study in which he was co-author Climate change in nature – Which suggested that the global stratification of the oceans had increased by 5.3 percent from 1960 to 2018 – had “profound and worrying” implications.
These included potentially more intense hurricanes driven by warming ocean surfaces.
And in February, research a Geoscience of nature found that the northern expanse of the Gulf Stream – the vast ocean current that carries heat that influences Europe’s climate and sea level in the United States – was the weakest in more than a thousand years, probably due to the climate change.
They said rising rainfall and the melting of Greenland’s ice sheet have increased fresh water in the upper ocean, disrupting the normal cycle that carries warm, salty surface water north from the equator. and sends deep low-salinity waters south.
© France-Presse Agency