A sharp increase in algal blooms, which is an important indicator of global warming

These findings came from Chinese researchers at the University of Shenzhen, based on 760,000 images from NASA’s Aqua satellite. she publish their results Wednesday in the scientific journal nature.

The Chinese also investigated the reasons for the increased blooms, by comparing water currents and sea temperature on the one hand and the average frequency of algae blooms on the other. The higher the temperature, the more frequent algal blooms will be in many areas. In some regions, particularly in Asia, algal blooms were more likely to be related to fertilizer use.

The total area where algal blooms occur increased by 3.97 million square kilometers compared to 2003. On average, coastal algal blooms occurred twice as often in recent years compared to 2003, the researchers estimated.

negative effects

The amount of plankton and algae (of which there are several thousand species) in seawater is an important indicator of global warming. More nutrients and warmer water increase algae blooms in the upper layers of the water, which initially provide food for other organisms. There are also negative effects: some algae blooms produce toxic substances, such as the well-known blue-green algae, which can also lead to fish deaths, odors and other inconveniences to humans in the hot summer. Layers of dead algae at the bottom can also lead to anoxic “dead zones” in the ecosystem.

Lennart de Nooijer, an oceanographer at the Netherlands Institute for Marine Research (NIOZ), describes the method of this research as particularly fascinating. “By analyzing satellite images, you get a picture that you can’t get by taking water samples from boats,” he says. At the same time, he has a caveat: the photos give you no idea how much algae has actually accumulated on the sea floor. And you don’t get an impression of any toxic substances produced by the algae.

Measuring algal blooms is important for mapping the effects of climate change. According to De Nooijer, the key question is what is the net effect of carbon dioxide absorption and emission2 in the cycle between plankton and the organisms that live on them. Algae, like other plants, absorb carbon dioxide2 above from the air. They, in turn, are eaten by animals that absorb carbon dioxide2 emit again. The basic question is what is the percentage size of carbon dioxide2 is that the network disappears in that cycle,” says de Noijer.

Benefits and risks of flowering

In 2019, the researchers stated from the German research institute Marum has already proven that the composition of plankton in the sea has changed due to global warming. At a rate of 40 km every ten years, the so-called Foraminifera has advanced about 600 km in the past two centuries into previously cooler parts to the north. At the same time, species that thrive in colder waters are declining in number and size.

Chinese researchers believe their detailed information about the size and frequency of algal blooms on the coast can provide insight into how these blooms form and disappear. With this information, the risks and benefits of flowering can be assessed. The authors concluded that it could also help develop strategies to reduce the consequences of harmful blooms.

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Megan Vasquez

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