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Detection of Pacific tropical water variability by taut-line moorings in the western equatorial Pacific

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Abstract

This study uses temperature and salinity time series acquired with taut-line moorings in the western equatorial Pacific to investigate water mass behavior on the thermocline layer. Basically, it is insufficient to trace water mass variation by the original discrete depth coordinate data because of relatively high variability of density at fixed depth near the thermocline. A reconstruction method based on the density surface motion caused by tidal forcing was used to derive continuous profiles of temperature and salinity from vertically discrete measurements at fixed depths. This method can represent detailed vertical salinity structures and their variation, especially along the potential density surface of 24.8σθ, where the salinity maximum of South Pacific tropical water (SPTW) appeared. Variability around the 24.8σθ surface at each site was as large as that observed at the surface, which suggests a strong influence of SPTW behavior. High salinity along the 24.8σθ surface within the equatorial band of the western Pacific appeared during boreal fall-winter at sites far from New Guinea. In contrast, high salinity appeared near New Guinea during the boreal spring-summer. These features suggest the influence of the New Guinea Coastal Undercurrent. Over longer time scales, several higher salinity events were observed. The most pronounced salinity event occurred during 2007–2008. Interannual variation of the salinity anomaly along the 24.8σθ surface was negatively correlated with the Niño 3.4 sea surface temperature anomaly. A long-term salinity anomaly shift from negative to positive occurred around the end of 2002. The relationship with decadal variation in subtropical cell transport is also discussed.

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Acknowledgments

We thank the members of the TRITON project. The TRITON moorings were deployed and recovered by R/V MIRAI, R/V KAIYO, and R/V YOKOSUKA. The TRITON project is supported by the Ministry of Education, Culture, Sports, Science and Technology, Japan. The authors acknowledge Dongxiao Zhang for the useful discussion about the decadal variation of STC transport. The Niño 3.4 SST anomaly data were downloaded from http://www.cpc.ncep.noaa.gov/data/indices/.

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  1. Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa, 237-0061, Japan

    Iwao Ueki & Kentaro Ando

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  1. Iwao Ueki
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  2. Kentaro Ando
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Correspondence to Iwao Ueki.

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Ueki, I., Ando, K. Detection of Pacific tropical water variability by taut-line moorings in the western equatorial Pacific. J Oceanogr 69, 429–441 (2013). https://doi.org/10.1007/s10872-013-0184-6

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  • DOI: https://doi.org/10.1007/s10872-013-0184-6

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