We are grateful to Susan Hautala, Sabine Mecking, and David Darr for many helpful discussions. Suggestions by two anonymous reviewers greatly improved this manuscript. This work was supported by the National Aeronautics and Space Administration, through an Earth System Science Graduate Fellowship (Ladd) and the TOPEX extended mission (960910), and the National Science Foundation (OCE-9818920).
Alexander, M. A., 1992: Midlatitude atmosphere–ocean interaction during El Niño. Part I: The North Pacific Ocean. J. Climate,5, 944–958.
——, and C. Deser, 1995: A mechanism for the recurrence of wintertime midlatitude SST anomalies. J. Phys. Oceanogr.,25, 122–137.
Bingham, F. M., 1992: Formation and spreading of subtropical mode water in the North Pacific. J. Geophys. Res.,97, 11 177–11 189.
Bjerknes, J., 1966: A possible response to the atmospheric Hadley circulation to equatorial anomalies of temperature. Tellus,18, 820–829.
Budyko, M. I., 1956: Teplovoi Balans Zemnoi Poverkhnosti (The Heat Balance of the Earth’s Surface). Gidrometeorologicheskoi Izdatel’stvo, 255 pp. (Translated by N. A. Stepanova, U.S. Weather Bureau.).
Bunker, A. F., 1976: Computations of surface energy flux and annual air–sea interaction cycles of the North Atlantic Ocean. Mon. Wea. Rev.,104, 1122–1140.
da Silva, A. M., C. C. Young, and S. Levitus, 1994: Atlas of Surface marine Data 1994. Vol 1: Algorithms and Procedures, NOAA Atlas NESDIS 6, 51 pp.
De Miranda, A. P., B. Barnier, and W. K. Dewar, 1999: Mode waters and subduction rates in a high-resolution South Atlantic simulation. J. Mar. Res.,57, 213–244.
Esbensen, S. K., and Y. Kushnir, 1981: The heat budget of the global ocean: An atlas based on estimates from surface marine observations. Oregon State University Climate Research Institute Rep. 29, 27 pp.
Fine, R. A., R. Lukas, R. M. Bingham, M. J. Warner, and R. H. Gammon, 1994: The western equatorial Pacific: A water mass crossroads. J. Geophys. Res.,99, 25 063–25 080.
Gu, D., and S. G. H. Philander, 1997: Interdecadal climate fluctuations that depend on exchanged between the tropics and extratropics. Science,275, 805–807.
Hallberg, R., 1995: Some aspects of the circulation in ocean basins with isopycnals intersecting sloping boundaries. Ph.D. dissertation, University of Washington, 244 pp.
Hautala, S. L., and D. H. Roemmich, 1998: Subtropical mode water in the northeast Pacific basin. J. Geophys. Res.,103, 13 055–13 066.
Hazeleger, W., and S. S. Drijfhout, 2000: Eddy subduction in a model of the subtropical gyre. J. Phys. Oceanogr.,30, 677–695.
Huang, R. X., and B. Qiu, 1994: Three-dimensional structure of the wind driven circulation in the subtropical North Pacific. J. Phys. Oceanogr.,24, 1608–1622.
Inui, T., K. Takeuchi, and K. Hanawa, 1999: A numerical investigation of the subduction process in response to an abrupt intensification of the westerlies. J. Phys. Oceanogr.,29, 1993–2015.
Isemer, H. J., and L. Hasse, 1987: The Bunker Climate Atlas of the North Atlantic Ocean. Vol. 2. Springer-Verlag, 252 pp.
Kraus, E. B., and J. S. Turner, 1967: A one-dimensional model of the seasonal thermocline: II. The general theory and its consequences. Tellus,19, 98–106.
Ladd, C. A., and L. Thompson, 2000: Formation mechanisms for North Pacific central and eastern subtropical mode waters. J. Phys. Oceanogr.,30, 868–887.
Ledwell, J. R., A. J. Watson, and C. S. Law, 1993: Evidence for slow mixing across the pycnocline from an open-ocean tracer-release experiment. Nature,364, 701–703.
Levitus, S., and T. P. Boyer, 1994: World Ocean Atlas 1994. Vol 4: Temperature, NOAA Atlas NESDIS 4, 117 pp.
——, R. Burgett, and T. P. Boyer, 1994: World Ocean Atlas 1994. Vol 3: Salinity. NOAA Atlas NESDIS 3, 99 pp.
Marsh, R., and A. L. New, 1996: Modeling 18° Water variability. J. Phys. Oceanogr.,26, 1059–1080.
——, A. J. G. Nurser, A. P. Megann, and A. New, 2000: Water mass transformation in the Southern Ocean of a global isopycnal coordinate GCM. J. Phys. Oceanogr.,30, 1013–1045.
Masuzawa, J., 1969: Subtropical mode water. Deep-Sea Res.,16, 463–472.
——, 1972: Water characteristics of the North Pacific Central Region. Kuroshio—Its Physical Aspects, H. Stommel and K. Yoshida, Eds., University of Tokyo Press, 235–352.
McCartney, M., 1982: The subtropical recirculation of mode waters. J. Mar. Res.,40 (Suppl.), 427–464.
Miller, A. J., D. R. Cayan, and J. M. Oberhuber, 1994: On the re-emergence of midlatitude SST anomalies. Proc. 18th Annual Climate Diagnostic Workshop, Boulder, CO, NOAA, 149–152.
Nakamura, H., 1996: A pycnostad on the bottom of the ventilated portion in the central subtropical North Pacific: Its distribution and formation. J. Oceanogr.,52, 171–188.
Namias, J., and R. M. Born, 1970: Temporal coherence in North Pacific sea surface temperatures. J. Geophys. Res., 75, 5952–5955.
——, and ——, 1974: Further studies of temporal coherence in North Pacific sea-surface temperature patterns. J. Geophys. Res.,79, 797–798.
Nonaka, M., S.-P. Xie, and K. Takeuchi, 2000: Equatorward spreading of a passive tracer with application to North Pacific interdecadal temperature variations. J. Oceanogr.,56, 173–183.
Nurser, A. J. G., R. Marsh, and R. G., Williams, 1999: Diagnosing water mass formation from air–sea fluxes and surface mixing. J. Phys. Oceanogr.,29, 1468–1487.
Philander, S. G. H., 1990: El Niño, La Niña and the Southern Oscillation. Academic Press, 293 pp.
Roden, G. I., 1970: Aspects of the mid-Pacific transition zone. J. Geophys. Res.,75, 1097–1109.
——, 1972: Temperature and salinity fronts at the boundary of the subarctic–subtropical transition zone in the western Pacific. J. Geophys. Res.,77, 7175–7187.
Schneider, N., A. J. Miller, M. A. Alexander, and C. Deser, 1999: Subduction of decadal North Pacific temperature anomalies: Observations and dynamics. J. Phys. Oceanogr.,29, 1056–1070.
Speer, K., 1997: A note on average cross-isopycnal mixing in the North Atlantic. Deep-Sea Res.,44, 1981–1990.
——, and E. Tziperman, 1992: Rates of water mass formation in the North Atlantic Ocean. J. Phys. Oceanogr.,22, 93–104.
——, H. J. Isemer, and A. Biastoch, 1995: Water mass formation from revised COADS data. J. Phys. Oceanogr.,25, 2444–2457.
——, S. Rintoul, and B. Sloyan, 1997: Subantarctic mode water formation by air–sea fluxes. Int. WOCE Newsl.,29, 29–31.
Suga, T., K. Hanawa, and Y. Toba, 1989: Subtropical mode water in the 137°E section. J. Phys. Oceanogr.,19, 1605–1618.
——, Y. Takei, and K. Hanawa, 1997: Thermostad distribution in the North Pacific subtropical gyre: The central mode water and the subtropical mode water. J. Phys. Oceanogr.,27, 140–152.
Talley, L. D., 1988: Potential vorticity distribution in the North Pacific. J. Phys. Oceanogr.,18, 89–106.
Tziperman, E., and K. Speer, 1994: A study of water mass transformation in the Mediterranean Sea: Analysis of climatological data and a simple 3-box model. Dyn. Atmos. Oceans,21, 53–82.
Walin, G., 1982: On the relation between sea-surface heat flow and thermal circulation in the ocean. Tellus,34, 187–195.
Warner, M. J., J. L. Bullister, D. P. Wisegarver, R. H. Gammon, and R. F. Weiss, 1996: Basin-wide distributions of chlorofluorocarbons CFC-11 and CFC-12 in the North Pacific: 1985–1989. J. Geophys. Res.,101, 20 525–20 542.
White, W. B., 1995: Design of a global observing system for gyre-scale upper ocean temperature variability. Progress in Oceanography, Vol. 36, Pergamon, 169–217.
Worthington, L. V., 1959: The 18°C water in the Sargasso Sea. Deep-Sea Res.,5, 297–305.
Yuan, X., and L. D. Talley, 1996: The subarctic frontal zone in the North Pacific: Characteristics of frontal structure from climatological data and synoptic surveys. J. Geophys. Res.,101, 16 491–16 508.
Zhang, R.-H., L. M. Rothstein, and A. J. Busalacchi, 1998: Origin of upper-ocean warming and El Niño change on decadal scales in the tropical Pacific Ocean. Nature,391, 879–883.