Why the weirdest sea level changes on Earth are happening off the coast of Japan
The ocean's surface is far from flat, with seas rising and falling in response to trade winds, gravity, and the movement of warm water currents. These currents, like the Kuroshio, are crucial in regulating ocean temperatures and influencing local ecosystems. However, recent changes in the Kuroshio's position and behavior have triggered record-warm ocean temperatures and disrupted fisheries, an integral part of Japanese culture.
The Kuroshio, or 'Black Current', is one of the world's largest water streams, typically traveling north from the equator and banking east around Japan's Boso peninsula. In recent years, it has been behaving unusually, with its northern edge shifting as much as 300 miles farther poleward, leading to unprecedented warm waters in the surrounding region. This shift has had dramatic repercussions, including record-warm ocean temperatures and disrupted fisheries.
The Kuroshio's movement is influenced by the Hadley Cell, a global zone of warm, rising air across the tropics, which is expanding due to climate change. This expansion shifts rainfall patterns and the zones of sinking air that anchor high-pressure systems, such as the Pacific High, which in turn affects the currents. As a result, the Kuroshio Extension has been moving north, partly due to the atmospheric shift.
The impact of these changes on Japan's fisheries is significant. In central Japan, a major mackerel fishery has been disrupted, with catches falling to less than half of what they were 10 years ago. Northeastern Japan's Sanriku coast, known for its rich fisheries, has also been affected, with the Kuroshio Extension displacing the Oyashio current and bringing on a stark change in ocean temperature.
The future of these changes is uncertain, but scientists are concerned about the potential for more volatility. The Kuroshio's position could continue to fluctuate, and its intensity may become larger, according to Bo Qiu, a leading Kuroshio expert. The impact of climate change on these changes is also unclear, but there are mounting reasons to implicate greenhouse gases and a changing climate.
These extreme ocean events offer a unique opportunity to learn what the oceans will be like 100 years from now, according to Sugimoto. Understanding how these changes have altered the seas of Tohoku provides a chance to understand how the world's oceans will change in the future.
