Scientists warn of ‘marine heatwaves’, but what is it?


Global climate warming in recent years has a strong impact not only on the weather on land, but also affects the oceans. Moreover, it is not only about the destruction of glaciers and the rise in water levels, but also the growth of the average temperature. This creates great risks for the animals and plants that live in it. Especially dangerous, according to scientists, are marine heatwaves. As the effects of global warming on the planet become more pronounced, marine heatwaves are becoming a frequent and intense phenomenon. They cause serious damage to the ecosystem, which persists for a long time even after the water has cooled. But what are marine heatwaves in general, why do they arise?

What are marine heatwaves?

Marine heat waves are sudden bursts of water temperature to abnormally high values ​​that can last at least five days. And sometimes the high temperature of the water lasts for several weeks or even months. The term “marine heatwave” was first used in 2010-2011, when waters off western Australia warmed to record levels. This instilled in the death of a huge number of algae, scallops and other inhabitants of the ocean.

At that time, nothing was known about this phenomenon to science, but since then scientists have begun to actively study it. Moreover, the climate contributed to this – sea heat waves began to occur more often. In 2016, a massive heat wave was recorded off the coast of Chile, causing an algae bloom that destroyed fish farms.

Marine heatwaves destroy entire ecosystems

From 2015 to 2019, heatwaves have repeatedly occurred in the Mediterranean Sea. This led to the mass death of algae and corals. Over the past two years, scientists’ attention has been riveted to New Zealand, where the highest ocean temperatures on record have been observed.

Why Marine HeatWaves Occur

There are different reasons for the occurrence of marine heat waves. For example, an event in Western Australia was caused by an increase in the Leeuwen Current, which brought an increased amount of warm water from the Indian Ocean. The 2015-2016 heatwaves in the Tasman Sea between Australia and New Zealand were caused by an increase in the East Australian Current, which is moving south of the Coral Sea.

There are various reasons for the occurrence of heat waves. A 2019 study found that 60 percent of marine heatwaves in the southwest Atlantic Ocean were caused by heat domes. Recall that this phenomenon occurs when a high-pressure area “parks” in a certain zone and does not allow cold air flows. As a result, the air in the high pressure zone becomes very hot.

Most often, heat waves are caused by various ocean currents.

When the thermal dome is over the sea, it prevents the cool air from forming storms and churning the water. As a result, the water stratifies and an abnormally warm layer appears on the surface.

How global warming affects heatwaves

Despite the fact that the causes of marine heat waves are different, global warming increases their number. For this reason, they become more frequent and intense. Experts estimate that as a result of burning fossil fuels, the ocean absorbs 90% more heat. As a result, the temperature of the upper layer of water, about 700 meters deep, has increased by almost one degree since 1901. It is logical to assume that in warmer water, certain parts of the ocean periodically begin to heat up to higher temperatures than they used to be.

A 2020 study published in the journal Science says that the number of marine heat waves has increased more than 20 times since 1981 due to global warming. However, scientists still do not know much about this phenomenon. According to Nicholas Bond, a researcher at the University of Washington and a Washington State climate scientist, scientists are not yet sure why heat waves sometimes last so long.

Heatwaves kill forests of algae that absorb carbon dioxide from the atmosphere

According to one version, when the surface of the ocean heats up, it radiates heat into the atmosphere. This prevents the formation of cloud cover. As a result, sea water receives even more sunlight, so the process of its heating continues. That is, there is a vicious circle.

“There has to be something else that keeps the sea warm,” says Nicholas Bond.

Finally, we note that the consequences of marine heat waves cannot be underestimated. Since the events of 2010–2011, entire kelp forests have died in Western Australia. The disappearance of marine vegetation leads not only to the destruction of ecosystems, but also to a detrimental effect on the Earth’s atmosphere. The fact is that algae forests are 20 times more efficient at absorbing carbon dioxide than ordinary forests. Therefore, scientists are trying to artificially restore forests of algae. For this, they even breed starfish, as we talked about earlier. Without forests of algae, the process of global warming will occur even faster.

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