For sustainable society


Brightening clouds to prevent coral bleaching

In some areas, the phenomenon of “bleaching,” where coral reefs that are supposed to be colorful turn white, is rapidly advancing. It means that the phytoplankton with pigment that live inside the coral is reduced due to climate change and sea pollution, and the coral itself seems to have turned white.

This is thought to be due to rising sea temperatures in the long run because of global warming and the short-term El Nino phenomenon in which the seawater temperature rises above normal. Damage to the Great Barrier Reef, the largest coral reefs in the world, is serious, and in order to protect corals, research teams at the Sydney Institute of Marine Science and Southern Cross University challenged new attempts this spring.

They worked on a technique called “cloud brightening,” which artificially increases the surface area of ​​the clouds and reflects more sunlight. Clouds are condensation nucleus, which are collections of water droplets that consist of particles such as dust in the air. With this technology, the amount of the condensation nucleus can be increased to make the clouds more expanded by spraying fine particles of salt created from seawater toward the clouds.

The experiment was conducted near Broadhurst Reef, 100km off the coast of Townsville in Far North Queensland. A sprayer was installed on a large ship and tested the hypothesis at one-tenth of the scale that they were aiming for. The research team reported that the results were confirmed using drones and research vessels. It was confirmed to produce hundreds of trillions of salt crystals per second that expand the size of the clouds that reflect sunlight.

The research team plans to triple the scale next year for their tests and plans to increase it ten times two years later, which makes it possible to cover an area of ​​400 square kilometers. In addition, over the next four years, researchers from multiple institutions will also investigate the environmental risks that can be caused by this artificial technology. Changes in rainfall patterns, both in the ocean and on land, are expected.

In the Great Barrier Reef, three large-scale bleachings have occurred in the last five years. According to AFP, one-third of the 2,300km coral reefs are suffering from bleaching, and the seawater temperature in this February was the highest ever since the measurement in 1900. It is the first time for bleaching to occur in all northern, central, and southern regions of the Great Barrier Reef.

By the way, although corals are often regarded as plants, actually they are animals. Symbiotic phytoplankton, which is reduced by bleaching, is a zooxanthella that provides the corals with nutrients produced by photosynthesis. On the other hand, zooxanthella coexists by being protected by hard corals to prevent being eaten by zooplankton and by receiving excrement and carbon dioxide produced by corals. We must remember that beautiful coral reefs are not only a tourism resource for humans but also part of the ecosystem in the sea.


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