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Using Indian Ocean earthquake to tell rate of global warming

Date: 22 September 2020 Tags: Space

Issue

Scientists have developed a novel method to determine how fast the Indian Ocean is warming by analysing the sound from seabed earthquakes.

 

Background

This advance that may lead to a relatively low-cost technique to monitor water temperatures in all of the oceans.

 

Details

  • According to the researchers, as much as 95% of the extra heat trapped on the Earth by greenhouse gases like carbondioxide is held in the world’s oceans, making it important to monitor the temperature of ocean waters.

  • In the current study, the scientists used existing seismic monitoring equipment, as well as historic data on earthquakes, to determine how much the temperature of the ocean has altered, and continues changing, even at depths that are normally out of the reach of conventional tools.

  • They assessed a 3000-kilometer-long section in the equatorial East Indian Ocean, and found temperature fluctuations between 2005 and 2016, with a decadal warming trend that “substantially exceeds previous estimates.

  • By one estimate, the scientists said the ocean could be warming by nearly 70% greater than had been believed.

 

   Methodology

  • The method works by monitoring underwater quake sounds, which are powerful and travel long distances through the ocean without significantly weakening.

  • When an earthquake happens under the ocean, most of its energy travels through the earth, but a portion of that energy is transmitted into the water as sound.

  • The sound waves propagate outward from the quake’s epicenter just like seismic waves that travel through the ground, but added that the sound moves at a much slower speed.

  • The ground waves arrive at a seismic monitoring station first, followed by the sound waves, which will appear as a secondary signal of the same event.

  • Since the speed of sound in water increases as the water’s temperature rises, they found that the length of time it takes a sound wave to travel a given distance in the ocean can be used to deduce the water’s temperature.

  • The scientists said analysing earthquakes which happen again and again in the same place can shed more information on the rate of warming.

  • It takes about a half hour for them to travel that distance to a particular spot, with water temperature causing about one-tenth-of-a second difference. It’s a very small fractional change, but can be measured.

  • Based on the data analysed so far, the researchers confirmed that the Indian Ocean has been warming, as other data collected through other methods have indicated.

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