According to new research, underwater waves deep under the ocean’s surface (some as high as 500 meters) play an important role in the ocean’s heat and carbon storage. An international team of researchers led by the University of Cambridge, the University of Oxford and the University of California, San Diego measured the impact of these waves and other types of underwater turbulence in the Atlantic Ocean and found that their significance was minor. is accurately reflected in the climate models that shape government policy.
Most of the heat and carbon released by human activities is absorbed by the ocean, but how much it can absorb depends on turbulence on the ocean floor because heat and carbon are either pushed deep into the ocean or pulled to the surface. Although these underwater waves are already well known, their importance in transporting heat and carbon is not fully understood. Results published in the journal AGU Developmentsshows that turbulence in inland ocean waters is more important than previously thought for the transport of carbon and heat on a global scale.
Ocean circulation carries warm waters from the tropics to the North Atlantic, where they cool, sink, and return south, like a giant conveyor belt, into the deep ocean. The Atlantic arm of this circulation pattern, called the Atlantic Meridional Overturning Circulation (AMOC), plays a key role in regulating global temperature and the carbon budget. Ocean circulation redistributes heat to the polar regions, where it melts the ice, and to the ocean depths, where it can store carbon for thousands of years.
“If you take a picture of the ocean floor, you see a lot of complex dynamics,” said first author Dr Laura Kimoli, from Cambridge’s Department of Applied Mathematics and Theoretical Physics. “Under the surface of the water there are jets, currents and waves – in the deep ocean these waves can go up to 500 meters high, but they break just like waves on a beach.”
“The Atlantic Ocean is unique in how it affects global climate,” said author Dr Ali Mashayek, from Cambridge’s Department of Earth Sciences. “It has a strong circulation between the poles, from the upper reaches to the depths of the ocean. Water also moves faster on the surface than at the depths of the ocean.”
For the past few decades, researchers have investigated whether AMOC was a factor in why the Arctic lost so much ice cover as some Antarctic ice sheets grew. One possible explanation for this phenomenon is that it takes several hundred years for heat absorbed by the ocean in the North Atlantic to reach Antarctica.
Now, using a combination of remote sensing, ship measurements, and data from autonomous floating vehicles, Cambridge-led researchers have discovered that heat from the North Atlantic is reaching Antarctica much faster than previously thought. In addition, turbulence in the ocean, especially large underwater waves, plays an important role in the climate.
The ocean, like a giant cake, is made up of different layers, with colder, denser water at the bottom and warmer, lighter water at the top. Most of the heat and carbon transport in the ocean takes place within a given layer, but heat and carbon can also move between layers of density, returning deep waters to the surface. The researchers found that the movement of heat and carbon between layers is facilitated by minor turbulence, a phenomenon not fully represented in climate models.
Mixed estimates from various observing platforms showed evidence of small-scale turbulence in the upper part of the circulation, which is consistent with theoretical estimates of the ocean’s interior waves. Various estimates have shown that turbulence mostly affects the class of density layers associated with the deep water core moving southward from the North Atlantic to the Southern Ocean. This means that the heat and carbon carried by these water bodies have a good chance of moving at different density levels.
“Climate models take turbulence into account, but mostly how it affects ocean circulation,” Kimoli said. Said. “But we found that turbulence itself is vital and plays an important role in how much carbon and heat is absorbed by the ocean and where it is stored.”
“Many climate models have an oversimplified view of the role of microscale turbulence, but we’ve shown that it’s important and should be treated with more care,” Mashaek said. Said. “For example, its role in turbulence and ocean circulation controls how much anthropogenic heat reaches the Antarctic Ice Sheet and the timescale on which this occurs.”
The study provides a more accurate representation of small-scale turbulence in climate models to enable scientists to make more accurate predictions of the future effects of climate change.
Source: Port Altele
