March 17 () –
Giant underwater waves in the depths of the ocean surface, some up to 500 meters highplay an important role in how the ocean stores heat and carbon.
An international team of researchers, led by the University of Cambridge, the University of Oxford and the University of California at San Diego, quantified the effect of these waves and other forms of submarine turbulence in the Atlantic Ocean and found that its importance is not being accurately captured in climate models.
The ocean absorbs most of the heat and carbon emitted by human activity, but how much it can absorb depends on turbulence within the ocean, as heat and carbon are pushed into the ocean depths or pulled out. the surface.
While these underwater waves are already well known, their importance in transporting heat and carbon is not fully understood.
The results, published in the AGU Advances magazineshow that turbulence within the oceans is more important for the transport of carbon and heat on a global scale than previously imagined.
Ocean circulation transports warm water from the tropics to the North Atlantic, where it cools, sinks, and returns south into the deep ocean. like a giant conveyor belt. The Atlantic branch of this circulation pattern, called the Atlantic Meridional Overturning Circulation (AMOC), plays a key role in regulating global heat and carbon balances. Ocean circulation redistributes heat to the polar regions, where it melts the ice, and carbon to the deep ocean, where it can be stored for thousands of years.
“If you were to take a picture of the interior of the ocean, you would see a lot of complex dynamics at work,” he said. it’s a statement first author Dr. Laura Cimoli, from Cambridge’s Department of Applied Mathematics and Theoretical Physics. “Below the surface of the water, there are jets, currents, and waves; in the deep ocean, these waves can be up to 500 meters high, but they break like a wave on the beach.”
“The Atlantic Ocean is special in the way it affects global climate,” said co-author Dr. Ali Mashayek from Cambridge’s Department of Earth Sciences. “It has a strong pole-to-pole circulation from its upper reaches to the depths of the ocean. Water also moves faster at the surface than in the deep ocean.”
For the past few decades, researchers have been investigating whether AMOC may be a factor explaining why the Arctic has lost so much ice cover, while some Antarctic ice sheets are growing. One possible explanation for this phenomenon is that heat absorbed by the ocean in the North Atlantic takes several hundred years to reach Antarctica.
Now, using a combination of remote sensing, ship-based measurements and data from autonomous floats, Cambridge-led researchers have discovered that North Atlantic heat may reach Antarctica much faster than previously thought. In addition, turbulence within the ocean, particularly large underwater waves, plays an important role in climate..
Like a giant cake, the ocean is made up of different layers, with cooler, denser water at the bottom and warmer, lighter water at the top. Most heat and carbon transport within the ocean occurs within a particular layer, but heat and carbon can also move between layers of density, bringing deep water back to the surface.
The researchers found that the movement of heat and carbon between layers is facilitated by small-scale turbulence, a phenomenon that is not fully represented in climate models.
Mixing estimates from different observing platforms showed evidence of small-scale turbulence in the upper branch of the circulation, consistent with theoretical predictions of internal ocean waves. The different estimates showed that the turbulence mainly affects the class of density layers associated with the core of deep water moving south from the North Atlantic to the Southern Ocean. This means that the heat and carbon carried by these water masses have a high probability of moving through different density levels.
“Climate models account for turbulence, but above all how it affects ocean circulation,” Cimoli said. “But we have found that turbulence is vital in its own right and plays a key role in how much carbon and heat is absorbed by the ocean and where it is stored.”
“Many climate models have an overly simplistic representation of the role of microscale turbulence, but we have shown that it is important and should be treated with more care,” Mashayek said. “For example, turbulence and its role in ocean circulation exert control over the amount of anthropogenic heat reaching the Antarctic ice sheet and the time scale over which that happens.”
The research suggests an urgent need to install turbulence sensors in global observing arrays and a more accurate representation of small-scale turbulence in climate models, to allow scientists to make more accurate projections of the future effects of climate change.
