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Climate change has brought about major changes in the stability of the oceans faster than previously thought, according to a study released Wednesday, sounding the alarm over its role as a global thermostat and the marine life it supports.
Research published in the journal Nature looked at 50 years of data and tracked how surface water “dissociates” from the deeper ocean.
Climate change has disrupted the mixing of the oceans, a process that helps store most of the world’s excess heat and a significant amount of CO2.
The water at the surface is warmer – and therefore less dense – than the water below, a contrast that is intensified by climate change.
Global warming is also causing massive amounts of fresh water to be discharged into the seas due to the melting of ice caps and glaciers, lowering the salinity of the top layer and further reducing its density.
This increasing contrast between the density of ocean layers makes mixing more difficult, so that oxygen, heat, and carbon are all less able to penetrate deep seas.
“Similar to a layer of water on top of oil, surface water in contact with the atmosphere mixes less effectively with the underlying ocean,” said lead author Jean-Baptiste Sallee of the Sorbonne University and the CNRS national scientific research center.
He said as 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 tracked 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 strengthened around the world – measured by density contrast – at a much higher rate than previously thought.
The researchers also found that, contrary to their expectations, winds reinforced by climate change had also acted to deepen the ocean’s surface layer by five to 10 meters per decade over the past half-century.
A significant number of marine animals live in this surface layer, with a food web dependent on phytoplankton.
But as the winds increase, the phytoplankton are churned deeper, away from the light that helps them thrive, potentially disrupting the larger food web.
These are “not small changes that only some experts care about,” Sallee told AFP.
“They represent a fundamental change in the underlying structure of our oceans. Far more pronounced than we have previously thought.”
Deep and unsettling
The oceans play a crucial role in mitigating the effects of climate change by absorbing about a quarter of human-made CO2 and absorbing more than 90% of the heat generated by greenhouse gases, according to the Group of intergovernmental experts on climate change (IPCC).
“But by stabilizing, the role of the ocean in cushioning climate change is made more difficult because it is more difficult for the ocean to absorb these enormous amounts of heat and carbon,” Sallee said.
Scientists are increasingly sounding the alarm about the potential implications of warming for our oceans.
In 2019, research published in the United States Proceedings of the National Academy of Sciences calculated that climate change would empty the ocean of nearly a fifth of all living creatures, measured in mass, by the end of the century.
Climate scientist Michael Mann warned in September that the findings of a study he co-authored Nature’s climate change – which suggested that the global stratification of the oceans increased by 5.3% from 1960 to 2018 – had “deep and disturbing” implications.
These included potentially more intense hurricanes caused by warming ocean surfaces.
And in February, research on Geoscience of nature found that the northern extension of the Gulf Stream – the vast heat-carrying ocean current that influences weather conditions in Europe and sea levels in the United States – was the lowest in more than a thousand years, possibly due to the climate change.
They said increased precipitation and the melting of the Greenland ice sheet increased fresh water in the upper ocean, disrupting the normal cycle that carries warm, salty surface water north. from the equator and returns deep, low salinity waters to the south.
© Agence France-Presse
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