[A-OS15] Physical Oceanography (General)

[AOS15-10] Seaglider observations of tropical water mass variability off the eastern coast of Taiwan

*Dai-Jyun Yu¹, Ming-Huei Chang¹, Sen Jan¹, Yu-Hsin Cheng² (1.Institute of Oceanography, National Taiwan University, Taipei, Taiwan, 2.Department of Marine Environmental Informatics, National Taiwan Ocean University, Keelung, Taiwan)

Keywords:Water masses, West Philippines Sea Tropical Water, North Pacific Tropical Water, South China Sea Tropical Water

We examine the tropical water mass variability using thousands of high-resolution CTD (salinity, temperature, and depth) profiles collected in 2016-2022 by Seaglider hydrographic observations primarily distributed off the eastern coast of Taiwan. In the context of the previous studies, the essential components of the water mass off the east coast of Taiwan encompass the West Philippines Sea Tropical Water (WPSTW), the North Pacific Tropical Water (NPTW), and the South China Sea Tropical Water (SCSTW). To better characterize the water mass features, we develop a method to quantify the water mass similarity to the above three components using the normalized root mean square (rms) difference of the salinity (S) and temperature (T) relative to the T-S curves of the three components along the isopycnals. This method successfully tracks and distinguishes water masses. We found that the water masses off the eastern coast of Taiwan are generally a mixture of WPSTW and NPTW but are closer to WPSTW. An exception occurred from late 2016 to early 2017, showing that the main component of water masses became NPTW, when the bifurcation point of NEC was located at its northmost position. This event was likely related to the interannual variation of the North Equatorial Current (NEC) bifurcation. The water mass deviated to SCSTW when Seaglider was around the Luzon Strait, presumably related to the mixing between SCSTW and WPSTW due to flow-topography interactions. In addition, the encounter of the mesoscale eddy with the Kuroshio could induce some variability of water mass.