North Pacific subtropical mode water, a vertically homogeneous thermocline water mass, occupies the entire subtropical Western Pacific Ocean. It transports mass, heat and nutrients from the surface to the subsurface ocean, providing memory of climate variability1,2,3,4,5,6,7,8,9,10,11. Decadal variability of the mode water temperature has been attributed to the Pacific Decadal Oscillation (PDO)2,3,12,13, but this is based on short data records. Here, using long records of observations, we show that decadal-to-multidecadal variability of the mode water mean temperature is instead controlled by the Atlantic Multidecadal Variability (AMV). During an AMV-positive phase, warm sea surface temperatures (SSTs) in the North Atlantic Ocean weaken the subtropical North Pacific westerlies; the associated anomalous easterlies in the subtropical west Pacific4,5 drive a northward Ekman transport of warm water to the mode water formation area. Subduction of the warm water increases mode water temperature, influencing Northwestern Pacific upper ocean heat content and fish catches. A long pre-industrial model simulation with multiple AMV cycles and a pacemaker experiment support this mechanism—the AMV forcing alone can drive decadal variability of the mode water. Thus, the AMV provides important memory for prediction of decadal climate and ecosystem variability in the Pacific Ocean.
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Data related to this paper can be downloaded from the following: Ishii data, https://rda.ucar.edu/datasets/ds285.3/; EN4 data, https://www.metoffice.gov.uk/hadobs/en4/; IAP data, http://22.214.171.124/cheng/; SODA data, https://climatedataguide.ucar.edu/climate-data/soda-simple-ocean-data-assimilation; NCEP data, https://www.esrl.noaa.gov/psd/; the PDO index, https://www.ncdc.noaa.gov/teleconnections/pdo/data.csv; the AMV index, https://climatedataguide.ucar.edu/climate-data/atlantic-multi-decadal-oscillation-AMO-index-station-based; the data of the PI-control experiment and pacemaker experiment are available at Ocean and Atmosphere Data Center of Ocean University of China, http://coadc.ouc.edu.cn/download/b.e10.B1850CN.f09_g16.001/ and http://coadc.ouc.edu.cn/download/Pacemaker_EXP/, respectively.
The CESM, developed by the NCAR, can be downloaded from http://www2.cesm.ucar.edu/.
Hanawa, K. & Talley, L. D. in Mode Waters: Ocean Circulation and Climate International Geophysical Series Vol. 77 (eds Siedler, G. et al.) 373–386 (Academic, 2001).
Oka, E. & Qiu, B. Progress of North Pacific mode water research in the past decade. J. Oceanogr. 68, 5–20 (2012).
Davis, X., Rothstein, L., Dewar, W. & Menemenlis, D. Numerical investigations of seasonal and interannual variability of North Pacific subtropical mode water and its implication for Pacific climate variability. J. Clim. 24, 2648–2665 (2011).
Wu, B., Lin, X. & Qiu, B. Meridional shift of the Oyashio Extension front in the past 36 years. Geophys. Res. Lett. 45, 9042–9048 (2018).
Wu, B., Lin, X. & Qiu, B. On the seasonal variability of the Oyashio Extension fronts. Clim. Dynam. 53, 7011–7025 (2019).
Masuzawa, J. Subtropical mode water. Deep Sea Res. 16, 463–472 (1969).
Feucher, C., Maze, G. & Mercier, H. Subtropical mode water and permanent pycnocline properties in the World Ocean. J. Geophys. Res. Oceans 124, 1139–1154 (2019).
Rainville, L., Jayne, S. R. & Cronin, M. F. Variations of the North Pacific subtropical mode water from direct observations. J. Clim. 27, 2842–2860 (2014).
Hanawa, K. Interannual variations in the wintertime outcrop area of subtropical mode water in the western North Pacific Ocean. Atmos. Ocean 25, 358–374 (1987).
Bingham, F. M. Formation and spreading of subtropical mode water in the North Pacific. J. Geophys. Res. Oceans 97, 11177–11189 (1992).
Oka, E. Seasonal and interannual variation of North Pacific subtropical mode water in 2003-2006. J. Oceanogr. 65, 151–164 (2009).
Oka, E. et al. Decadal variability of subtropical mode water subduction and its impact on biogeochemistry. J. Oceanogr. 71, 389–400 (2015).
Mantua, N. J., Hare, S. R., Zhang, Y., Wallace, J. M. & Francis, R. C. A Pacific interdecadal climate oscillation with impacts on salmon production. Bull. Am. Meteorol. Soc. 78, 1069–1079 (1997).
Sukigara, C. et al. Biogeochemical evidence of large diapycnal diffusivity associated with the subtropical mode water of the North Pacific. J. Oceanogr. 67, 77–85 (2011).
Qiu, B. et al. Observations of the subtropical mode water evolution from the Kuroshio extension system study. J. Phys. Oceanogr. 36, 457–473 (2006).
Cerovecki, I. & Giglio, D. North Pacific subtropical mode water volume decrease in 2006–2009 estimated from Argo observations: influence of surface formation and basin-scale oceanic variability. J. Clim. 29, 2177–2199 (2016).
Tian, Y., Uchikawa, K., Ueda, Y. & Cheng, J. Comparison of fluctuations in fish communities and trophic structures of ecosystems from three currents around Japan: synchronies and differences. ICES J. Mar. Sci. 71, 19–34 (2014).
Ishii, M., Kimoto, M., Sakamoto, K. & Iwasaki, S. Steric sea level changes estimated from historical ocean subsurface temperature and salinity analyses. J. Oceanogr. 62, 155–170 (2006).
Good, S. A., Martin, M. J. & Rayner, N. A. EN4: quality controlled ocean temperature and salinity profiles and monthly objective analyses with uncertainty estimates. J. Geophys. Res. Oceans 118, 6704–6716 (2013).
Cheng, L. et al. Improved estimates of ocean heat content from 1960–2015. Sci. Adv. 3, e1601545 (2017).
Carton, J. A. & Giese, B. S. A reanalysis of ocean climate using simple ocean data assimilation (SODA). Mon. Weath. Rev. 136, 2999–3017 (2008).
Sugimoto, S., Hanawa, K., Watanabe, T., Suga, T. & Xie, S. P. Enhanced warming of the subtropical mode water in the North Pacific and North Atlantic. Nat. Clim. Change 7, 656–658 (2017).
Enfield, D. B., Mestas-Nunez, A. M. & Trimble, P. J. The Atlantic multidecadal oscillation and its relation to rainfall and river flows in the continental US. Geophys. Res. Lett. 28, 2077–2080 (2001).
Mcgregor, S. et al. Recent Walker circulation strengthening and Pacific cooling amplified by Atlantic warming. Nat. Clim. Change 4, 888–892 (2014).
Li, X., Xie, S. P., Gille, S. T. & Yoo, C. Atlantic-induced pan-tropical climate change over the past three decades. Nat. Clim. Change 6, 275–279 (2016).
Sun, C. et al. Western tropical Pacific multidecadal variability forced by the Atlantic multidecadal oscillation. Nat. Commun. 8, 15998 (2017).
Lyu, K. & Yu, J. Y. Climate impacts of the Atlantic Multidecadal Oscillation simulated in the CMIP5 models: A re-evaluation based on a revised index. Geophys. Res. Lett. 44, 3867–3876 (2017).
Hurrell, J. W. et al. The community earth system model: a framework for collaborative research. Bull. Am. Meteorol. Soc. 94, 1339–1360 (2013).
Zhang, R. & Delworth, T. L. Impact of the Atlantic Multidecadal Oscillation on North Pacific climate variability. Geophys. Res. Lett. 34, 229–241 (2007).
Yu, L., Jin, X. & Liu, H. Poleward shift in ventilation of the north Atlantic subtropical underwater. Geophys. Res. Lett. 45, 258–266 (2017).
Kalnay, E. et al. The NCEP/NCAR 40-year reanalysis project. Bull. Am. Meteorol. Soc. 77, 437–472 (1996).
Qiu, B. & Kelly, K. A. Upper-ocean heat balance in the Kuroshio Extension region. J. Phys. Oceanogr. 23, 2027–2041 (1993).
Uehara, H., Suga, T., Hanawa, K. & Shikama, N. A role of eddies in formation and transport of North Pacific subtropical mode water. Geophys. Res. Lett. 30, 1705 (2003).
Marshall, J. C., Williams, R. G. & Nurser, A. J. G. Inferring the subduction rate and period over the north Atlantic. J. Phys. Oceanogr. 23, 1315–1329 (1993).
Nishikawa, S., Tsujino, H., SakAMVto, K. & Nakano, H. Effects of mesoscale eddies on subduction and distribution of subtropical mode water in an eddy-resolving OGCM of the Western North Pacific. J. Phys. Oceanogr. 40, 1748–1765 (2010).
Toyoda, T. et al. Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses. Clim. Dynam. 49, 891–907 (2017).
Cushman-Roisin, B. Subduction. In Dynamics of the Oceanic Surface Mixed Layer, Hawaiian Winter Workshop Proc. (eds Muller, P. & Henderson, D.) 181–196 (Univ. Hawaii at Manoa, 1987).
Qiu, B. & Huang, R. X. Ventilation of the North Atlantic and North Pacific: subduction versus obduction. J. Phys. Oceanogr. 25, 2374–2390 (1995).
Da Costa, M. V., Mercier, H. & Treguier, A. M. Effects of the mixed layer time variability on kinematic subduction rate diagnostics. J. Phys. Oceanogr. 35, 427–443 (2005).
Chen, J., Qu, T., Sasaki, Y. N. & Schneider, N. Anti-correlated variability in subduction rate of the western and eastern North Pacific Oceans identified by an eddy-resolving ocean GCM. Geophys. Res. Lett. 37, L23608 (2010).
Xu, L., Xie, S.-P., McClean, J. L., Liu, Q. & Sasaki, H. Mesoscale eddy effects on the subduction of North Pacific mode waters. J. Geophys. Res. Oceans 119, 4867–4886 (2014).
Bretherton, C. S., Widmann, M., Dymnidov, V. P., Wallace, J. M. & Blade, I. The effective number of spatial degrees of freedom of a time-varying field. J. Clim. 12, 1990–2009 (1999).
X.L. is supported by China’s National Key Research and Development Projects (2016YFA0601803) and the National Natural Science Foundation of China (41925025 and U1606402). B.W. is supported by the China Scholarship Council (201806330010). L.Y. thanks the NOAA for support for her study on climate change and variability.
The authors declare no competing interests.
Peer review information Nature Climate Change thanks Xichen Li and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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a, Time series of detrend mode water temperature anomaly (black from Ishii data, blue from EN4 data, yellow from IAP data, purple from SODA data) and the normalized PDO index (red) smoothed by a 7-year low-pass filter. The shadings for each line show the one standard deviations of their time series. The grey shadings indicate a cold period (1970–1980) and a warm period (2000–2010) of the mode water, respectively. b, Lead-lag correlation between the low-pass filtered detrend mode water temperature anomaly (black from Ishii data, blue from EN4 data, yellow from IAP data) and the PDO index during the period of 1945–2012. c, Same as (b), but only for the period of 1978–2012.
a, Mean temperature gradient (shading, unit in oC/10 m) during the cold period derived from the Ishii data. Black solid contours show the mean potential temperature for the cold period (1970–1980) and the dashed contours are their climatology. The marked 16 °C and 18 °C contours are the defined upper and lower temperature boundaries of the mode water, and the marked 12 °C contours present the main thermocline depth. The white contour is the 1.5 °C/100 m line, which is the vertical temperature gradient criterion of the mode water (see Methods). b, Same as (a), but for the warm period 2000-2010. c, Time series of detrend mode water thickness (unit in m, black) from the Ishii data and the normalized AMV index (red) for the period 1945–2012 (thin lines) and 7-year running averages (thick lines). Correlation coefficient between the mean depth and AMV at zero lag is -0.85. d, Same as (c), but for the mode water mean depth (unit in m, black). Correlation coefficient between the mode water thickness and AMV at zero lag is 0.83.
Extended Data Fig. 3 Variation of the mixed layer depth and main thermocline depth in the mode water area.
a, Time series of detrend mixed layer depth (MLD, unit in m, black) from the Ishii data and the normalized AMV index (red) for the period 1945-2012 (thin lines) and 7-year running averages (thick lines). Correlation coefficient between the MLD and AMV at zero lag is -0.80. b, MLD anomaly (unit in m) during the cold period. The contour intervals are 2 m and the thick contours indicate the value of 4 m. c, MLD anomaly (unit in m) during the warm period. The contour intervals are 2 m and the thick contours indicate the value of -4 m. d, Same as (a), but for the main thermocline depth (MTD, see Methods, unit in m). Correlation coefficient between the MTD and AMV at zero lag is -0.82. e, MTD anomaly (unit in m) during the cold period. The contour intervals are 5 m and the thick contours indicate the value of 5 m. f, MTD anomaly (unit in m) during the warm period. The contour intervals are 5 m and the thick contours indicate the value of -5 m.
a, Regressions of the SST (shading, unit in oC) and surface wind filed (vector, unit in m/s) with respect to the AMV index derived from the pre-industrial model simulation (PI-Control EXP.). Green line indicates the transect A (150°E, 20°-50°N). b, Temperature regressed upon the AMV index, derived from the PI-Control EXP., along transect A. c, Time series of mode water mean temperature and the normalized model AMV index (red) from the PI-Control EXP. smoothed by a 7-year low-pass filter. Correlation coefficient between the mode water mean temperature and the model AMV at zero lag is 0.76. The shading shows the one standard deviations of its time series.
a, Net heat flux (Qnet) anomaly (units in W/m2) in the cold period of 1970-1980 derived from the NCEP data set. The black box indicates the formation area (130°E-180°, 28°-35°N) and the subduction area (130°E-180°, 20°-28°N) of the mode water. b, SST anomalies induced by Ekman heat transport (shading, units in oC) and anomalous wind fields (vector, unit in m/s) in the mode water formation and subduction area during the cold period 1970-1980 derived from the Ishii and NCEP data sets.
In the Atlantic Ocean, observed SST trend (unit in oC/36 yr) from 1979-2014 was added in the modelled mixed layer temperature in the restoring forcing. In the other areas, the mixed-layer temperature was restored to the model climatology. Then the climate response to the restored ocean temperature was calculated by the difference between the Pacemaker experiment and a control experiment, in which the mixed-layer temperature was restored to the model climatology.
Extended Data Fig. 7 Transient simulation for the mechanism of the mode water controlled by the AMV.
a, Anomalous SST (shading, unit in oC) from the Pacemaker model experiment (Pacemaker EXP.) for the AMV positive phase (mode water warm phase) in the first year. Green line indicates the transect A (150°E, 20°-50°N). b, Temperature anomaly derived from Pacemaker EXP. during the AMV positive phase, along transect A, in the first year. c, d and e, f, Same as (a), (b), but for the second year and last 10 years. Contours show the mean temperature for each year and the marked 16 oC and 20 oC contours are the defined upper and lower temperature boundaries of the mode water in the Pacemaker EXP., and the marked 12 oC contours present the main thermocline depth (see Methods).
a, Ocean heat content density anomalies (OHCa, shading, unit in × 106 J/m3) along transect A during cold period derived from the Ishii data. Black solid contours show the mean potential temperature for the cold period (1970-1980) and the dashed contours are their climatology. The marked 16 oC and 18 oC contours are the defined upper and lower temperature boundaries of the mode water, and the marked 12 oC contours present the main thermocline depth. The white contour is the 1.5 oC/100 m line, which is the vertical temperature gradient criterion of the mode water (see Methods).
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Wu, B., Lin, X. & Yu, L. North Pacific subtropical mode water is controlled by the Atlantic Multidecadal Variability. Nat. Clim. Chang. 10, 238–243 (2020). https://doi.org/10.1038/s41558-020-0692-5
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