Scientists have found a clever new way to measure ocean warming, using sound waves from underground earthquakes.
Researchers say the “hack” works because the sound travels faster in heated water.
The team looked at sonic data from the Indian Ocean emitted by the tremors over a 10-year period.
As the oceans have warmed up due to global warming, scientists have seen the speed of sound waves increase.
Their new method shows that the Indian Ocean’s decades-long warming trend was much higher than previously estimated.
It is important for climate scientists to have accurate information about the warming of our oceans.
They realize that about 90% of the energy trapped in our atmosphere by greenhouse gases is absorbed by the oceans.
However, accurately measuring temperature at multiple locations and depths is a huge challenge.
Deployed about 4,000 autonomous devices called Argo capture temperature information which helps a lot, but there is a huge gap in our knowledge.
This is especially true of what is happening in waters deeper than 2,000 meters.
But now a team of researchers has developed a completely different method that exploits the fact that the speed of sound in seawater depends on temperature.
This concept was first proposed and judged using sound waves generated by scientists in the late 1970s.
However, concerns about the impact of these terms on marine mammals and the increasing cost have abandoned the idea.
The new method involves using naturally generated sound waves that occur during subterranean earthquakes.
Scientists tested data on more than 4,000 tremors in the Indian Ocean between 2004 and 2016.
The team then looked for a pair of earthquakes with “repeaters”, almost identical sources and strengths.
By measuring how long these slow-moving signals took across the water from Indonesia to a monitoring station on Diego Garcia Island, they were able to execute temperature changes for the entire ocean over a 10-year period.
Lead author of the California Institute of Technology. “It takes about half an hour to get to Diego Garcia from Sumatra,” Venbo told BBC News.
“Due to the change in the temperature of the deep sea between Sumatra and Diego Garcia, this half-hour journey time varies from a few tenths of a second.
“Since we can measure these variations very accurately, we can estimate small changes in the average temperature of the deep sea, in this case about a tenth of a degree.”
The author says the system has some major advantages, as it is capable of delivering a large-scale average temperature over a 3,000-kilometer route from Sumatra to Diego Garcia, minimizing the effects of local fluctuations, essentially making it more accurate over the sea.
The method is also quite inexpensive, as it uses data already collected and is more sensitive to temperature than the current 2,000m limit.
Scientists have shown in their research that the warming in the Indian Ocean over the decades that they studied was higher than previously estimated.
However, there are some important cavities in the paper
“It’s important to emphasize that this is a result that applies to this particular region and this particular decade,” Dr. Wu said.
“We need to apply our method in many more regions and at different time frames to assess whether there is any systematic or more-or-less-estimated global deep-sea trend.
“It’s too early to make a decision in this regard.”
To make the concept work globally, scientists will need access to more underwater receptors.
At the moment, the research team is working on data collected by a hydrophone network operated by the UN Comprehensive Nuclear-Test-Ban Treaty Organization, which is listening for submarine nuclear explosions.
These hydropower plants receive signals from 10,000 shallow submarine earthquakes worldwide each year, Dr. Wu explained.
“All of this information contains information on deep sea temperature changes – it’s just waiting for us to figure it out.”
The study was published in the journal Science.
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