The Kuroshiro Current running along the Pacific coast that is responsible for Japan's plentiful marine bounty has made a large curve south off the coast of the Tokai region for the first time in 12 years, the Japan Meteorological Agency (JMA) has announced. The Mainichi Shimbun asked experts how the shift in the world's largest current will affect daily life.
"This time the shift has made a classic large serpentine curve, and it is expected to continue flowing this way for some time to come," said senior scientist Toru Miyama of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC)'s Environmental Variability Prediction and Application Research Group. "It's rare globally for an ocean current like the Kuroshio to make such a large curve for a long period of time. There will be various effects on fishing, tide levels and weather in every region."
According to Miyama, there was a small curve in surface ocean currents southeast of Kyushu at the end of March this year. The shift split into two currents, but each one continued east for several months while growing in size, meeting in August to create a larger "W" shaped curve in the waters south of the Japanese archipelago. One of the currents shifted east of Japan, but the second stabilized off the Tokai coast and stopped moving, becoming the largest shift of its kind in 12 years.
While the current is flowing this way, tide levels mainly in the Tokai and Kanto regions can rise several dozen centimeters, and residents along the coast have to be cautious of flood damage. In the northern part of the southward-flowing Kuroshiro Current, sea levels will rise and the water temperature will drop, forming a large counter-clockwise flowing cold water eddy.
Along the Tokai and Kanto coastline, due to the pull from this eddy, it is highly possible a portion of the Kuroshio Current will be pulled from east to west in what is known as a Kuroshio countercurrent, and the rotation of the Earth will cause tide levels to rise on the right side of the current in respect to its flow throughout the Northern Hemisphere. Additionally, because the temperature of the warm Kuroshio Current is higher than that of surrounding waters, it will have a higher volume and sea levels will also rise.
The JMA reports that when a large serpentine curve occurred in the Kuroshiro Current in October 1979, Typhoon Tip left in its wake 115 dead or missing, caused heavy damage to 1,426 buildings, and flooding damage to 56,099 buildings both above and below floor level nationwide. At the time, tide levels in Omaezaki, Shizuoka Prefecture, had risen several dozen centimeters because of the Kuroshio curve, and that is thought to have been one of the causes of the widespread flooding damage. This time as well, the JMA warns, "There is a possibility of flooding and other damage in low-lying areas along the coast occurring during fall, when tide levels are the highest of the year."
From another perspective, the head of a monitoring group at the Marine Fisheries Research and Development Center (JAMARC) at the National Research Institute of Fisheries Science, Satoshi Seto, says, "The fishing location for the season's first catch of the skipjack tuna will change, and it may also affect the size of the catch."
The habitat of the season's first skipjack tuna is ocean waters at or above 19 degrees Celsius. Because the fish ride the warm Kuroshio Current northward along the Japanese coastline from March to May, the shift in the current could move the fishing grounds further from the coast than average years. Because of this, small fishing boats that use nets to catch the tuna will be unable to reach the fishing areas and the fishery yield may drop, the center says.
According to JAMARC, during the previous large current shift which lasted from July 2004 to August 2005, fishing yields for skipjack tuna were lower than average in places like Mie, Tokushima and Kochi prefectures, but where the Kuroshio Current came close to the coast, such as in Chiba and Kagoshima prefectures, the skipjack tuna catch was plentiful.
"As this hasn't happened in 12 years, fishermen will surely be bewildered by the shift in their usual fishing areas," predicts Seto. "In ocean regions where there are strong currents like the Kuroshio, fishermen may not be able to catch the elusive 'kinmedai' fish (splendid alfonsino), and depending on the route of the current, there may be areas which have a bountiful catch of mackerel."
Along with changes in the sea, because the curve in the Kuroshio affects the temperature distribution on the ocean surface, there is research that suggests there is a higher possibility of snowfall in the Tokyo metropolitan area as the course of low air pressure fronts shift offshore.