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Global ocean waters can accelerate warming, make them less livable



Reduced mixing up and down is expected to have huge implications beyond simply accelerating global warming. It is projected to increase the energy available for hurricanes and other storms, reduce the essential nutrients for fish in the upper ocean and reduce the oceans’ ability to store carbon, among other impacts.

The study assesses how the separation of seawater layers, known as stratification, has changed based on new data on temperature, salinity and density. He found that significant changes had taken place as the ocean absorbed more heat in the upper 6,500 feet of water.

The study, conducted by researchers from China as well as the United States, found that stratification increased by about 5.3% between 1

960 and 2018, by a percentage of 0.9% per decade.

The way the ocean layers are separated is similar to the basic vinaigrette salad dressing, where a lighter butter sits on top and a thicker vinegar is located near the bottom. Once shaken, the layers are mixed to form the familiar dressing. What is happening in the oceans now is that there is less shaking.

Ocean trends are particularly significant because the computer models used to simulate how climate change is likely to develop do not involve such a rapid increase in ocean stratification, which may cause them to reduce future warming rates.

Most of the stratification trends, the study found, are due to the rapid warming of the highest 700 feet of water, which over time becomes fresher and lighter. The ocean heat content in the upper ocean has reached record levels as the oceans continue to absorb most of the added heat from global warming.

The results also suggest a reduced ability of the oceans to act as a massive carbon-saving bill, otherwise known as a carbon sink. The ocean absorbs huge amounts of carbon dioxide annually and it circulates by mixing in the deep ocean to stay there for decades or more.

A more divided ocean, with less exchange between layers, means there may be less carbon absorption over longer periods of time. This could lead to more carbon dioxide in the atmosphere, which will lead to greater and faster global warming.

The results are also important for understanding changes in the ocean’s ability to support marine life, as water overturning helps extract nutrients from the depths, and some parts of the globe are already seeing a reduction in the amount of oxygen available in the upper layers of the sea. ocean waters.

The study also reveals problems for some of the world’s most important ocean currents, which are driven by the exchange of lighter surface waters and deeper, colder and saltier ocean layers.

One such current is the global ocean conveyor, officially known as the Atlantic Meridian Meridian Circulation Circle, of which the Gulf Stream is a part. This circulation sends warm, salty waters north to the upper Atlantic, where the water becomes saltier and denser and sinks as it flows south into the southern hemisphere.

The Gulf Stream is helping to mitigate Europe’s climate and is playing an important role in intensifying storms off the east coast of the United States.

This current helps distribute heat around the world and regulate the burial of carbon in the oceans. Studies show that as Greenland’s ice sheet melts and releases lighter freshwater into the North Atlantic, that current slows.

Consequences of the hurricane season

The results show that there may be more energy to power future hurricanes and other storms that draw their strength in part from warm ocean waters.

“So many key impacts (ocean bioavailability, carbon sequestration, surface warming and effects on eg hurricane intensity) are affected by ocean stratification and changes,” said study co-author Michael Mann. Institute of Earth and Environmental Systems at Pennsylvania State University, by email.

Mann said the results show that hot water is bottled closer to surface water, which could lead to more frequent hurricanes and more intense and water-laden storms.

“I think this may play a role in the trend towards greater hurricane activity in ocean areas such as the tropical North Atlantic, which are warming rapidly. The abnormal heat in the tropical Atlantic this year was a key ingredient in our pre-season forecast for a hyperactive season, ”said Mann.

Paul Durac, a researcher at the Lawrence Livermore National Laboratory in California, who has published studies on the effects of climate change on ocean currents, says the study “fills a gap” in the scientific literature by quantifying the rate of change. But, he said, the new estimates may still be too low.

“I wouldn’t be surprised if this study underestimates the observed change,” he said in an email. Durac did not participate in the new study.


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