The Kuroshio is a strong western boundary current in the North Pacific, and transports warm, saltier waters from low to middle latitudes, which has a significant impact on China, East Asia and global climate.
However, limited by the scarcity of observational data, how the Kuroshio changed before the Industrial Revolution remains poorly understood.
Recently, the research team led by Prof. HU Shijian from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) have investigated the Porites coral Sr/Ca ratios from southern Taiwan island, which can record the long-term variability of the Kuroshio.
The study was published in Global and Planetary Change on Oct. 18.
Considering that the Kuroshio strongly affects the sea surface hydrographic conditions, changes in sea surface temperature can be used as an indirect indicator of changes in the Kuroshio.
Researchers found that the monthly coral Sr/Ca ratio, a reliable proxy for sea surface temperature, could record the interannual changes of Kuroshio transport, and they then used it to generate a continuous reconstruction of Kuroshio transport during the period from 1788 to 2013.
"The data shows a consistent decline in Kuroshio transport since 1788, with the rate of decline increasing since the 1950s, probably due to rapid oceanic warming," said LI Xiaohua, first author of this study. "In addition, the shift of bifurcation latitude of the North Equatorial Current, the phase transition of the Pacific Decadal Oscillation and El Niño-Southern Oscillation have also influenced the changes of the Kuroshio."
"This study presents a case study on ocean current changes using coral geochemical indexes, and fossil corals can be used in the future to trace paleocurrent changes," said Prof. HU, the corresponding author.
Comparison of Kuroshio transport reconstructed from the coral Sr/Ca for southeastern Taiwan island (KTSTW, black) and the 3-year running averages of the global ocean heat content (OHC) for the 0–700 m layer (EN4 dataset, orange) and western Pacific Warm Pool OHC enclosed by the 28 °C isotherm (EN4, dataset, purple).
Li, X. H., Guo, X., Jiang, H., Lu, X., Zhang, Z., Ma, J. and Hu, S. J.* (2024). Long-term variability of the Kuroshio since 1788 based on coral records. Global and Planetary Change, 104611.
(Text by LI Xiaohua)
Media Contact:
ZHANG Yiyi
Institute of Oceanology
E-mail: zhangyiyi@qdio.ac.cn
(Editor: ZHANG Yiyi)