Abstract
Using the data of conductivity-temperature-depth (CTD) intensive observations conducted during Oct.–Nov. 2005, this study provides the first three-dimension quasi-synoptic description of the circulation in the western North Pacific. Several novel phenomena are revealed, especially in the deep ocean where earlier observations were very sparse. During the observations, the North Equatorial Current (NEC) splits at about 12°N near the sea surface. This bifurcation shifts northward with depth, reaching about 20°N at 1 000 m, and then remains nearly unchanged to as deep as 2 000 m. The Luzon Undercurrent (LUC), emerging below the Kuroshio from about 21°N, intensifies southward, with its upper boundary surfacing around 12°N. From there, part of the LUC separates from the coast, while the rest continues southward to join the Mindanao Current (MC). The MC extends to 2 000 m near the coast, and appears to be closely related to the subsurface cyclonic eddies which overlap low-salinity water from the North Pacific. The Mindanao Undercurrent (MUC), carrying waters from the South Pacific, shifts eastward upon approaching the Mindanao coast and eventually becomes part of the eastward undercurrent between 10°N and 12°N at 130°E. In the upper 2 000 dbar, the total westward transport across 130°E between 7.5°N and 18°N reaches 65.4 Sv (1 Sv = 10−6 m3s−1), the northward transport across 18°N from Luzon coast to 130°E is up to 35.0 Sv, and the southward transport across 7.5°N from Mindanao coast to 130°E is 27.9 Sv.
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References
Bingham F M, Lukas R. 1994. The southward intrusion of North Pacific Intermediate Water along the Mindanao coast. J. Phys. Oceanogr., 24: 141–154.
Fine R A, Lukas R, Bingham F M et al. 1994. The western equatorial Pacific: A water mass crossroad. J. Geophs. Res., 99(12): 25 063–25 080.
Firing E, Kashina Y, Hacker P. 2005. Energetic subthermocline currents observed east of Mindanao. Deep-Sea Res. II, 52: 605–613.
Gordon A L. 1986. Interocean exchange of the thermohaline water. J.Geophys. Res., 91: 5 037–5 046.
Hu D. 1989. A thought on the role of western Pacific Ocean circulation in climate change in southeast China. Chin, J. Oceanol. Limnol., 7(1): 93–94.
Hu D, Cui M. 1989. The Western Boundary Current in the Far-Western Pacific Ocean. In: Progress of Western International Meeting and Workshop on TOGA CORAE, May 24–30, Picaut J, Lukas R, Delcroix T, eds, Noumea, New Caledonia., p123–134.
Hu D, Cui M C. 1991. The western boundary current of the Pacific and its role in the climate, J. Oceanol. Limnol., 9(1): 1–14.
Hu D, Cui M C, Qu T et al. 1991. A Subsurface Northward Current off Mindanao Identified by Dynamic Calculation. In: Oceanography of Asian Marginal Seas, Elsevier. p. 359–365
Kaneko I, Takatsuki Y, Kamiya H. 2001. Circulation of intermediate and deep waters in the Philippine Sea, J. Oceanogr., 57: 397–420.
Kashino Y, Watanabe H, Herunad B et al., 1999. Current variability at the Pacific entrance of the Indonesian Throughflow, J. Geophys. Res., 104: 11 021–11 035.
Liu Q, Pan A J, Liu Z Y. 2003. Intraseasonal oscillation and baroclinic instability of upper layer ocean in the North Equator Current, J. Oceanol. Limnol., 34(1): 94–100.
Lukas R, Firing E, Hacher B et al. 1991. Observations of the Mindanao Current during the Western Equatorial Pacific Ocean Circulation Study (WEPOCS). J. Geophs. Res., 96: 7 098–7 104.
Lukas R, Yamagata T, McCreary J P et al. 1996. Pacific low-latitude western boundary currents and the Indonesia throughflow, J. Geophs. Res., 101: 12 209–12 216.
McCreary J P, Lu P. 1994. On the interaction between the subtropical and the equatorial oceans: The subtropical cell. J. Phys. Oceanogr., 24: 466–497.
Nitani H. 1972. Beginning of the Kuroshio, In: Kuroshio: Physical Aspects of Japan Current. University of Washington Press, p.129–163
Nonaka M, Xie S. 2003. Co-variations of sea surface temperature and wind over the Kuroshio and its extension: Evidence for ocean-to-atmospheric feedback. J. Climate, 16: 1 404–1 413.
Qiu B, Lukas R. 1996. Seasonal and interannual variability of the North Equatorial Current, the Mindanao Current, and the Kuroshio along the Pacific western boundary. J. Geophs. Res., 101(5): 12 315–12 330.
Qu T, Lukas R. 2003. The bifurcation of the North Equator Current in the Pacific. J. Phys. Oceanogr., 33: 5–18.
Qu T, Meyers G, Godfrey J S et al. 1997a. Upper ocean dynamics and its role in maintaining the annual mean western Pacific warm pool in a global GCM, Int. J. Climatol., 17: 711–724.
Qu T, Kagimoto T, Yamagata Y. 1997b. A subsurface countercurrent along the east coast of Luzon. Deep-sea Res. I., 44: 431–423.
Qu T, Mistudera H, Yamagata T. 1998. On the western boundary currents in the Philippine Sea. J. Geophs. Res., 103(4): 7 537–7 548.
Qu T, Mitsudera H. Yamagata T. 1999. A climatology of the circulation and water mass distribution near the Philippine coast. J. Phys. Oceanogr., 29: 1 488–1 505.
Reid J L.1965. Intermediate waters of the Pacific Ocean, Johns Hopkins Oceanogr. Stud., 2: 85.
Toole J M, Millard R C, Wang Z et al. 1990. Observations of the Pacific North Equatorial Current bifurcation at the Philippine coast. J. Phys. Oceanogr., 20: 307–318.
Uda M, Hasunuma K. 1969. The eastward subtropical countercurrent in the western north Pacific. J. Oceanogr., 25: 201–210.
Wang F, Hu D. 1998a. Dynamic and thermohaline properties of the Mindanao Undercurrent I Dynamic structure. Chin. J. Oceanol. Limnol., 16(2): 122–127.
Wang F. Hu D. 1998b. Dynamic and thermohaline properties of the Mindanao Undercurrent II thermohaline structure. Chin. J. Oceanol. Limnol., 16(3): 206–213.
Wang F, Chang P, Hu D et al. 2002. Circulation in the western tropic Pacific Ocean and its seasonal variation. Chin Sci. Bul., 47(7): 591–595.
Wijffels S, Firing E, Toole J. 1995. The mean structure and variability of the Mindanao Current at 8°N. J. Geophs. Res, 100: 18 421–18 435.
Wyrtki K. 1961. Physical Oceanography of the Southeast Asian Waters, NAGA Report 2, Ins. of Oceanogr., University of California, San Diego, La Joola, CA. p.195.
Xie L, Tian J, Hu D et al. 2009. A quasi-synoptic interpretation of the water mass distribution and circulation in the western North Pacific I. Water mass distribution. Chin. J. Oceanol. Limnol., 27(3): 630–639.
Zang N. 2008. The Distribution of Several Western Boundary Undercurrents and the Corresponding Dynamic Mechanism. Ph D Dissertation. Institute of Oceanography, Chinese Academia Science.
Zhou H. 2006. A Study of Some Characteristics and Variability of the North Pacific Western Boundary Current System. PhD. Dissertation. Ocean University of China.
Zhou H, Xu J, Guo P et al. 2006. A summary on studies of western boundary current system in the North Pacific Ocean. J. Mar. Science, 24: 49–59.
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Supported by National Natural Science Foundation of China (Nos, 40890153 and 40576016)
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Xie, L., Tian, J., Hu, D. et al. A quasi-synoptic interpretation of water mass distribution and circulation in the western North Pacific II: Circulation. Chin. J. Ocean. Limnol. 27, 955–965 (2009). https://doi.org/10.1007/s00343-009-9240-x
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DOI: https://doi.org/10.1007/s00343-009-9240-x