Abstract
A water mass characterized by the pycnostad on the bottom of the ventilated portion in the central subtropical North Pacific is described through the comparison with the Subtropical Mode Wate (STMW). In this paper, this water mass is called the North Pacific Central Mode Water (CMW), because of its vertical homogeneity. The distribution of CMW is examined based on the climatological maps of annual mean potential vorticity. On the other hand, its formation area is examined based on the climatological winter temperature data set and the STD sections across the Kuroshio Extension in early spring of individual years. The main results are summarized as follows: 1) STMW is formed in the deep winter mixed layer south of the main path of the Kuroshio Extension (termed 12°C Front in this paper). On the other hand, CMW is formed in the deep winter mixed layer in the east-west band surrounded by a branch of the Kuroshio Extension (termed 9°C Front in this paper) and the boundary of two water masses representing the subtropical and subpolar gyres. 2) The winter mixed layer between the 12°C Front and the 9°C Front is shallower than that in the CMW and STMW formation areas. 3) These geographical features of the winter mixed layer depths near the subarcticsubtropical transition zone result in two pycnostads (STMW and CMW) in the main thermocline of the subtropical North Pacific through the advection caused by the subtropical gyre.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Hanawa, K. (1987): Interannual variations in the winter-time outcrop area of Subtropical Mode Water in the western North Pacific Ocean.Atmosphere-Ocean,25, 358–374.
Hanawa, K. and I. Hoshino (1988): Temperature structure and mixed layer over the Izu Ridge.J. Mar. Res.,46, 683–700.
Kawai, H. (1972): Hydrography of the Kuroshio Extension. p. 235–352.Kuroshio, It's Physical Aspects, ed. by H. Stommel and K. Yoshida, University of Tokyo Press.
Keffer, T. (1985): The ventilation of the world's oceans: Maps of the potential vorticity field.J. Phys. Oceanogr.,15, 509–523.
Levitus, S. (1982): Climatological atlas of the world ocean. NOAA Prof. Paper 13, 173 pp.
Luyten, J. R., J. Pedlosky and H. Stommel (1983): The ventilated thermocline.J. Phys. Oceanogr.,13, 282–309.
Marshall, J. C., A. J. G. Nurser and R. G. Williams (1993): Inferring the subduction rate and period over the North Atlantic.J. Phys. Oceanogr.,23, 1315–1329.
Masuzawa, J. (1969): Subtropical mode water.Deep-Sea Res.,16, 463–472.
Masuzawa, J. (1972): Water characteristics of the North Pacific central region. p. 95–127.Kuroshio, It's Physical Aspects, ed. by H. Stommel and K. Yoshida, University of Tokyo Press.
McCartney, M. S. (1982): The subtropical recirculation of Mode Waters.J. Mar. Res.,40 (suppl.), 427–464.
McCartney, M. S. and L. D. Talley (1982): The subpolar mode water of the North Atlantic.J. Phys. Oceanogr.,12, 1169–1188.
McDowell, S., P. Rhines and T. Keffer (1982): North Atlantic potential vorticity and its relation to the general circulation.J. Phys. Oceanogr.,12, 1417–1436.
Mizuno, K. and W. B. White (1983): Annual and interannual variability in the Kuroshio current system.J. Phys. Oceanogr.,13, 1847–1867.
Rhines, P. B. and W. R. Young (1982): A theory of wind-driven circulation of the world ocean 1. Mid-ocean gyres.J. Mar. Res.,40, (suppl.), 559–596.
Roden, G. I. (1970): Aspects of the mid-Pacific transition zone.J. Geophys. Res.,75, 1097–1109.
Roden, G. I. (1972): Temperature and salinity fronts at the boundary of the subarctic-subtropical transition zone in the western Pacific.J. Geophys. Res.,77, 7175–7187.
Suga, T. and K. Hanawa (1990): The mixed-layer climatology in the northwestern part of the North Pacific subtropical gyre and the formation area of Subtropical Mode Water.J. Mar. Res.,48, 543–566.
Suga, T. and K. Hanawa (1995a): The Subtropical mode water circulation in the North Pacific.J. Phys. Oceanogr.,25, 958–970.
Suga, T. and K. Hanawa (1995b): Interannual variations of North Pacific Subtropical Mode Water in the 137°E section.J. Phys. Oceanogr.,25, 1012–1017.
Suga, T., K. Hanawa and Y. Toba (1989): Subtropical Mode Water in the 137°E section.J. Phys. Oceanogr.,19, 1605–1618.
Suga, T., Y. Takei and K. Hanawa (1995): Thermostad distribution in the North Pacific subtropical gyre: The Subtropical Mode Water and the Central Mode Water.J. Phys. Oceanogr (to be submitted).
Talley, L. D. (1988): Potential vorticity distribution in the North Pacific.J. Phys. Oceanogr.,18, 89–106.
Worthington, L. V. (1959): The 18° Water in the Sargasso Sea.Deep-Sea Res.,5, 297–305.
Yasuda, I., K. Okuda and M. Hirai (1992): Evolution of a Kuroshio warm-core ring—variability of the hydrographic structure.Deep-Sea Res.,39, (suppl.), 131–161.
Yuan, X. and L. D. Talley (1992): Shallow salinity minima in the North Pacific.J. Phys. Oceanogr.,22, 1302–1316.
Zhang, R. C. and K. Hanawa (1993): Features of the Water-Mass Front in the northwestern North Pacific.J. Geophys. Res.,98, 967–975.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Nakamura, H. A pycnostad on the bottom of the ventilated portion in the central subtropical North Pacific: Its distribution and formation. J Oceanogr 52, 171–188 (1996). https://doi.org/10.1007/BF02235668
Received:
Revised:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF02235668