The intermediate water in the Philippine Sea
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The intermediate water in the Philippine Sea* ZANG Nan1, 2, 3, 4, **, WANG Fan1, 2, 3, 4, SPRINTALL Janet5 1
CAS Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071,
2
Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China
3
Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266237, China
4
College of Marine Science, University of Chinese Academy of Sciences, Qingdao 266071, China
5
Scripps Institution of Oceanography, U.C. San Diego, La Jolla CA 92093-0230, U.S.A
China
Received Jan. 16, 2020; accepted in principle Apr. 3, 2020; accepted for publication May 19, 2020 © Chinese Society for Oceanology and Limnology, Science Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The dimensional and temporal distribution of Antarctic Intermediate Water (AAIW) and North Pacific Intermediate Water (NPIW) in the Philippine Sea were explored using Argo profiles and gridded Argo data. As the salinity minimum of intermediate water from mid-high latitude of the southern and northern hemisphere of the Pacific Ocean, the properties of AAIW and NPIW merge at about 10°N with different properties in the Philippine Sea. The core of AAIW is located below 600 dbar with potential density of 27≤σθ≤27.3 kg/m3 and salinity of 34.5≤S≤34.55. The core of NPIW is located between 300–700 dbar with potential density of 26.2≤σθ≤27 kg/m3 and salinity of 34≤S≤34.4. The volume of AAIW and NPIW during January 2004 to December 2017 is negatively correlated. The time series of AAIW and NPIW is dominated by significant periods of 6 and 8 months, respectively. The variations of AAIW and NPIW are mainly affected by volume transport through a 130°E section by the North Equatorial Current (NEC) and North Equatorial Undercurrent (NEUC). Keyword: the intermediate water; the Antarctic Intermediate Water; the North Pacific Intermediate Water; seasonal variation
1 INTRODUCTION The tropical Western Pacific is a region with a complex distribution of currents and water masses. The westward North Equatorial Current (NEC) bifurcates at the Philippine coast near 12°N into the northward Kuroshio and the southward Mindanao Current (MC) (Nitani, 1972; Toole et al., 1990; Qiu and Lukas, 1996) (Fig.1). There exist subsurface countercurrents beneath the surface currents, such as the Mindanao Undercurrent (MUC) beneath the MC (Hu and Cui, 1989, 1991; Qu et al., 1998; Firing et al., 2005; Kashino et al., 2005; Zhang et al., 2014; Wang et al., 2015), the Luzon Undercurrent (LUC) beneath the Kuroshio (Hu and Cui, 1989; Qu et al., 1997; Gao et al., 2012; Wang and Hu, 2012; Hu et al., 2013), and the North Equatorial Undercurrent (NEUC) beneath the NEC (Wang and Hu, 1998; Qu et al., 2012; Qiu et al., 2013) (Fig.1). Many water masses from mid to high latitudes
merge and mix in the tropical Western Pacific, including surface water masses—North Pacific Tropical Water (NPTW) and South Pacific Tropical Water (SPTW), and intermediate water mas
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