The Kuroshio Current is the “Gulf Stream” of the Pacific—the warm western boundary current of the North Pacific’s subtropical gyre. After branching off from the North Equatorial Current east of the Philippines, the Kuroshio flows more than 3000 kilometers past Taiwan to the southeast coast of Japan. By transporting enormous volumes of water, which carry large amounts of heat and salt northward from the tropics toward the polar regions, the Kuroshio plays a vital role in the circulation of the North Pacific Ocean and affects the climate as well as fisheries across the coastal regions of northeast Asia and southern Alaska.
Despite the Kuroshio’s basin-wide importance, few in situ measurements of this current have been made east of Taiwan. Now Jan et al. describe the results of nine ship-based surveys conducted at 23.75°N from September 2012 through September 2014. These data show tremendous variability in this boundary current, including its velocity, volume, flow structure, and heat and salt transport. The researchers report that the observed maximum velocity varied between 0.7 and 1.4 meters/second and was located at depths ranging from 20 to 100 meters. The distance between Taiwan’s east coast and the maximum velocity position varied from 12 to 103 kilometers, and the current’s width, as delineated by the 0.2 meter per second velocity contour, varied from 85 to 135 kilometers.
In addition, during three of the nine cruises, the team observed two velocity maxima in the current, a characteristic that had not been previously identified. The volume of water transported by the Kuroshio varied between 10.46 and 22.92 million cubic meters per second, with a corresponding heat transport (referenced to 0°C) of 0.838 × 1015 to 1.793 × 1015 watts and salt transport of 345.0 × 106 to 775.9 × 106 kilograms per second, values that fall within the range of previous estimates.
Although it remains uncertain whether these surveys captured the full range of the Kuroshio’s variability in the region, the researchers conclude that the differences they observed clearly demonstrate that east of Taiwan the Kuroshio is far from a stable boundary current. The authors suggest this study provides an important data set to help characterize the Kuroshio’s variability and to validate numerical simulations. (Journal of Geophysical Research: Oceans, doi:10.1002/2014JC010614, 2015)
—Terri Cook, Freelance Writer
Citation: Cook, T. (2015), Large variability measured in Kuroshio Current east of Taiwan, Eos, 96, doi:10.1029/2015EO035635. Published on 21 September 2015.