According to a study published Wednesday, climate change has brought about major changes in ocean stability, faster than previously thought, and alarming about its role as a global thermostat and the marine life that supports it.
The research published in the journal Nature looked at 50 years of data and tracked the way surface water “disconnects” from the deeper ocean.
Climate change has disrupted the mixing of the ocean, a process that helps store most of the world’s excess heat and a significant portion of CO2.
Water at the surface is warmer – and therefore less dense – than the water below, a contrast that is reinforced by climate change.
Global warming is also causing massive amounts of fresh water to be washed into the sea through melting ice sheets and glaciers, lowering the salinity of the top layer and further diminishing its density.
This increasing contrast between the density of the ocean layers makes mixing more difficult, so that oxygen, heat and carbon are all less able to penetrate into the deep seas.
“As with a layer of water on top of oil, the surface water that comes into contact with the atmosphere mixes less efficiently with the underlying ocean,” said lead author Jean-Baptiste Sallee of Sorbonne University and the French national scientific research center CNRS.
He said, while scientists knew this process was underway, “we show here that this change occurred much faster than previously thought: more than six times faster.”
The report used global temperature and salinity observations obtained between 1970 and 2018 – including those from electronically tracked marine mammals – with a focus on the summer months, which include more data.
It said the barrier layer separating the ocean surface and deep layers had been strengthened worldwide – as measured by contrast in density – at a much faster rate than previously thought.
Researchers also found that, contrary to their expectations, climate change-enhanced winds have also worked 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 relies on phytoplankton.
But as the wind increases, the phytoplankton are churned deeper, away from the light that helps them grow, potentially disrupting the wider food web.
These are “not minor changes that only some experts care about,” Sallee told AFP.
“They represent a fundamental change in the underlying structure of our oceans. Much more pronounced than what we have previously thought.”
Profound and disturbing
According to the Intergovernmental Panel for Climate Change (IPCC), the oceans play a critical role in mitigating the effects of climate change by absorbing about a quarter of man-made CO2 and more than 90 percent of the heat generated by greenhouse gases to record.
“But stabilizing makes the ocean’s role as a buffer for climate change more difficult as it makes it harder for the ocean to absorb these massive amounts of heat and carbon,” Sallee said.
Scientists are increasingly raising the alarm about the possible consequences of warming our oceans.
Research published in the US in 2019. Proceedings of the National Academy of Sciences calculated that by the end of the century, climate change would empty the ocean of nearly a fifth of all living things by mass.
Climate scientist Michael Mann warned in September that findings from a study he co-authored Nature Climate change – suggesting that global ocean stratification had increased 5.3 percent between 1960 and 2018 – had “profound and disturbing” implications.
These may include more intense hurricanes driven by warming ocean surfaces.
And in February, inquire in Nature Geoscience found that the northern extension of the Gulf Stream – the huge, heat-carrying ocean current that affects weather in Europe and sea level in the US – was the weakest in over a thousand years, likely due to climate change.
They said the increased rainfall and the melting of the Greenland Ice Sheet have increased freshwater in the upper ocean, pushing the normal cycle of warm, salty surface water from the equator to the north and deep water with low salinity back to the south. is disturbed.
© Agence France-Presse