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North Atlantic–Pacific salinity contrast enhanced by wind and ocean warming

Abstract

High salinities in the Atlantic and low salinities in the Pacific are critical ocean features, impacting ocean circulations and climate. Here, using observational data, we reveal that the Atlantic–Pacific salinity contrast has amplified during the past half-century. Notably, in the 0–800 m, 20°–40° N band, the Atlantic–Pacific salinity contrast increased by 5.9% ± 0.6% since 1965. A decomposition of heaving and spicing modes suggests vital contributions of wind and ocean warming, in addition to known surface freshwater fluxes. Specifically, ocean surface warming leads to poleward migration of thermocline outcrop zones, while surface wind changes cause upper-layer convergence in mid-latitudes. These processes lead to substantial upper-layer salinity increases in the North Atlantic but have much weaker signatures in the North Pacific, determined by the inter-basin difference in climatological salinities. This work highlights the complexity of ocean salinity response to climate change, underscoring the unexpected importance of wind- and heat-driven processes in the Atlantic–Pacific salinity contrast.

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Fig. 1: Ocean salinity changes derived from observational data.
Fig. 2: Salinity changes in the spicing and heaving modes.
Fig. 3: Salinity changes in the spicing mode and causes.
Fig. 4: Salinity changes in the heaving mode and causes.
Fig. 5: The heaving mode in CMIP6 models.
Fig. 6: Salinity changes in LICOM3 simulations.

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Data availability

All datasets used in this study are publicly available. The IAP data are available from http://www.ocean.iap.ac.cn/?navAnchor=home, the NCEI data are available from https://www.nodc.noaa.gov/OC5/indprod.html, the EN4 data are available from https://www.metoffice.gov.uk/hadobs/en4/download-en4-2-1.html, the WOA data are available from https://www.ncei.noaa.gov/products/world-ocean-atlas, the ERA5 data are available from https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5 and the CMIP6 model simulation data are available from https://esgf-node.llnl.gov/projects/cmip6/. The source of the base maps is available form https://www.eoas.ubc.ca/~rich/map.html.

Code availability

The model code (LICOM3-HIP v.1.0) along with the dataset and a 100 km case are available via Zenodo at https://doi.org/10.5281/zenodo.4302813 (ref. 68) and https://doi.org/10.5281/zenodo.7440403 (ref. 69). The MATLAB code for data analysis and graphing is available upon request.

References

  1. Cheng, L. et al. Improved estimates of changes in upper ocean salinity and the hydrological cycle. J. Clim. 33, 10357–10381 (2020).

    Google Scholar 

  2. Durack, P. J., Wijffels, S. E. & Matear, R. J. Ocean salinities reveal strong global water cycle intensification during 1950 to 2000. Science 336, 455–458 (2012).

    CAS  Google Scholar 

  3. Allan, R. P. et al. Advances in understanding large‐scale responses of the water cycle to climate change. Ann. N. Y. Acad. Sci. 1472, 49–75 (2020).

    Google Scholar 

  4. Boyer, T. P. Linear trends in salinity for the World Ocean, 1955–1998. Geophys. Res. Lett. 32, L01604 (2005).

    Google Scholar 

  5. Gould, W. J. & Cunningham, S. A. Global-scale patterns of observed sea surface salinity intensified since the 1870s. Commun. Earth Environ. https://doi.org/10.1038/s43247-021-00161-3 (2021).

  6. Antonov, J. I., Levitus, S. & Boyer, T. P. Steric sea level variations during 1957–1994: importance of salinity. J. Geophys. Res. Oceans 107, SRF 14-1–SRF 14-8 (2002).

    Google Scholar 

  7. Frederikse, T. et al. The causes of sea-level rise since 1900. Nature 584, 393–397 (2020).

    CAS  Google Scholar 

  8. Bourgeois, T., Goris, N., Schwinger, J. & Tjiputra, J. F. Stratification constrains future heat and carbon uptake in the Southern Ocean between 30° S and 55° S. Nat. Commun. 13, 340 (2022).

    CAS  Google Scholar 

  9. Liu, M., Vecchi, G., Soden, B., Yang, W. & Zhang, B. Enhanced hydrological cycle increases ocean heat uptake and moderates transient climate change. Nat. Clim. Change 11, 848–853 (2021).

    Google Scholar 

  10. Fu, Y., Li, F., Karstensen, J. & Wang, C. A stable Atlantic Meridional Overturning Circulation in a changing North Atlantic Ocean since the 1990s. Sci. Adv. 6, eabc7836 (2020).

    Google Scholar 

  11. Thornalley, D. J. R. et al. Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years. Nature 556, 227–230 (2018).

    CAS  Google Scholar 

  12. Behrenfeld, M. J. et al. Climate-driven trends in contemporary ocean productivity. Nature 444, 752–755 (2006).

    CAS  Google Scholar 

  13. Boyce, D. G., Lewis, M. R. & Worm, B. Global phytoplankton decline over the past century. Nature 466, 591–596 (2010).

    CAS  Google Scholar 

  14. Curry, R., Dickson, B. & Yashayaev, I. A change in the freshwater balance of the Atlantic Ocean over the past four decades. Nature 426, 826–829 (2003).

    CAS  Google Scholar 

  15. Skliris, N. et al. Salinity changes in the World Ocean since 1950 in relation to changing surface freshwater fluxes. Clim. Dyn. 43, 709–736 (2014).

    Google Scholar 

  16. Reagan, J., Seidov, D. & Boyer, T. Water vapor transfer and near-surface salinity contrasts in the North Atlantic Ocean. Sci. Rep. 8, 8830 (2018).

    Google Scholar 

  17. Singh, H. K. A., Donohoe, A., Bitz, C. M., Nusbaumer, J. & Noone, D. C. Greater aerial moisture transport distances with warming amplify interbasin salinity contrasts. Geophys. Res. Lett. 43, 8677–8684 (2016).

    Google Scholar 

  18. Held, I. M. & Soden, B. J. Robust responses of the hydrological cycle to global warming. J. Clim. 19, 5686–5699 (2006).

    Google Scholar 

  19. Cheng, L. et al. Improved estimates of ocean heat content from 1960 to 2015. Sci. Adv. 3, e1601545 (2017).

    Google Scholar 

  20. 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).

    Google Scholar 

  21. Levitus, S., Antonov, J. I., Boyer, T. P., Garcia, H. E. & Locarnini, R. A. Linear trends of zonally averaged thermosteric, halosteric, and total steric sea level for individual ocean basins and the world ocean, (1955–1959)–(1994–1998). Geophys. Res. Lett. 32, L16601 (2005).

    Google Scholar 

  22. Hu, S. et al. Interannual to decadal variability of upper-ocean salinity in the southern Indian Ocean and the role of the Indonesian throughflow. J. Clim. 32, 6403–6421 (2019).

    Google Scholar 

  23. Qu, T., Fukumori, I. & Fine, R. A. Spin‐up of the Southern Hemisphere Super Gyre. J. Geophys. Res. Oceans 124, 154–170 (2019).

    Google Scholar 

  24. Yang, H. et al. Poleward shift of the major ocean gyres detected in a warming climate. Geophys. Res. Lett. 47, e2019GL085868 (2020).

    Google Scholar 

  25. Durack, P. J. & Wijffels, S. E. Fifty-year trends in global ocean salinities and their relationship to broad-scale warming. J. Clim. 23, 4342–4362 (2010).

    Google Scholar 

  26. Liu, L. L. & Huang, R. X. The global subduction/obduction rates: their interannual and decadal variability. J. Clim. 25, 1096–1115 (2012).

    Google Scholar 

  27. Zika, J. D., Gregory, J. M., McDonagh, E. L., Marzocchi, A. & Clément, L. Recent water mass changes reveal mechanisms of ocean warming. J. Clim. 34, 3461–3479 (2021).

    Google Scholar 

  28. Beech, N. et al. Long-term evolution of ocean eddy activity in a warming world. Nat. Clim. Change 12, 910–917 (2022).

    Google Scholar 

  29. Hogg, A. M. et al. Recent trends in the Southern Ocean eddy field. J. Geophys. Res. Oceans 120, 257–267 (2015).

    Google Scholar 

  30. Whalen, C. B., MacKinnon, J. A. & Talley, L. D. Large-scale impacts of the mesoscale environment on mixing from wind-driven internal waves. Nat. Geosci. 11, 842–847 (2018).

    CAS  Google Scholar 

  31. Lago, V. et al. Simulating the role of surface forcing on observed multidecadal upper-ocean salinity changes. J. Clim. 29, 5575–5588 (2016).

    Google Scholar 

  32. Zhu, C. & Liu, Z. Weakening Atlantic overturning circulation causes South Atlantic salinity pile-up. Nat. Clim. Change 10, 998–1003 (2020).

    Google Scholar 

  33. Bingham, F. M., Foltz, G. R. & McPhaden, M. J. Seasonal cycles of surface layer salinity in the Pacific Ocean. Ocean Sci. 6, 775–787 (2010).

    CAS  Google Scholar 

  34. Foltz, G. R. & McPhaden, M. J. Seasonal mixed layer salinity balance of the tropical North Atlantic Ocean. J. Geophys. Res. Oceans 113, C02013 (2008).

    Google Scholar 

  35. Johnson, E. S., Lagerloef, G. S. E., Gunn, J. T. & Bonjean, F. Surface salinity advection in the tropical oceans compared with atmospheric freshwater forcing: a trial balance. J. Geophys. Res. Oceans 107, SRF 15-1–SRF 15-11 (2002).

    Google Scholar 

  36. Li, Y., Wang, F. & Han, W. Interannual sea surface salinity variations observed in the tropical North Pacific Ocean. Geophys. Res. Lett. 40, 2194–2199 (2013).

    Google Scholar 

  37. Reverdin, G., Kestenare, E., Frankignoul, C. & Delcroix, T. Surface salinity in the Atlantic Ocean (30° S–50° N). Prog. Oceanogr. 73, 311–340 (2007).

    Google Scholar 

  38. Häkkinen, S., Rhines, P. B. & Worthen, D. L. Warming of the global ocean: spatial structure and water-mass trends. J. Clim. 29, 4949–4963 (2016).

    Google Scholar 

  39. Sathyanarayanan, A., Köhl, A. & Stammer, D. Ocean salinity changes in the global ocean under global warming conditions. Part I: mechanisms in a strong warming scenario. J. Clim. 34, 8219–8236 (2021).

    Google Scholar 

  40. Lin, P. et al. LICOM model datasets for the CMIP6 Ocean Model Intercomparison Project. Adv. Atmos. Sci. 37, 239–249 (2020).

    Google Scholar 

  41. Eyring, V. et al. Overview of the Coupled Model Intercomparison Project Phase 6 (CMIP6) experimental design and organization. Geosci. Model Dev. 9, 1937–1958 (2016).

    Google Scholar 

  42. Zweng, M. M. et al. World Ocean Atlas 2018: Salinity Vol. 2 (ed. Mishonov, A.) (NOAA, NESDIS, 2019).

  43. Grist, J. P. et al. The roles of surface heat flux and ocean heat transport convergence in determining Atlantic Ocean temperature variability. Ocean Dyn. 60, 771–790 (2010).

    Google Scholar 

  44. Lee, S., Gong, T., Johnson, N., Feldstein, S. B. & Pollard, D. On the possible link between tropical convection and the northern hemisphere Arctic surface air temperature change between 1958 and 2001. J. Clim. 24, 4350–4367 (2011).

    Google Scholar 

  45. Levitus, S. et al. World Ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010. Geophys. Res. Lett. 39, L10603 (2012).

    Google Scholar 

  46. Levitus, S. et al. Global ocean heat content 1955–2008 in light of recently revealed instrumentation problems. Geophys. Res. Lett. 36, L07608 (2009).

    Google Scholar 

  47. Ren, Q. et al. Increasing inhomogeneity of the global oceans. Geophys. Res. Lett. 49, e2021GL097598 (2022).

    Google Scholar 

  48. Li, G. et al. Increasing ocean stratification over the past half-century. Nat. Clim. Change 10, 1116–1123 (2020).

    Google Scholar 

  49. Sallée, J.-B. et al. Summertime increases in upper-ocean stratification and mixed-layer depth. Nature 591, 592–598 (2021).

    Google Scholar 

  50. Schmidtko, S., Stramma, L. & Visbeck, M. Decline in global oceanic oxygen content during the past five decades. Nature 542, 335–339 (2017).

    CAS  Google Scholar 

  51. Bindoff, N. L. & McDougall, T. J. Diagnosing climate change and ocean ventilation using hydrographic data. J. Phys. Oceanogr. 24, 1137–1152 (1994).

    Google Scholar 

  52. Huang, R. X. in Heaving, Stretching and Spicing Modes: Climate Variability in the Ocean 61–160 (Springer, 2020).

  53. Wong, A. P. S., Bindoff, N. L. & Church, J. A. Large-scale freshening of intermediate waters in the Pacific and Indian oceans. Nature 400, 440–443 (1999).

    CAS  Google Scholar 

  54. Helm, K. P., Bindoff, N. L. & Church, J. A. Changes in the global hydrological-cycle inferred from ocean salinity. Geophys. Res. Lett. 37, L18701 (2010).

    Google Scholar 

  55. Skliris, N., Zika, J. D., Nurser, G., Josey, S. A. & Marsh, R. Global water cycle amplifying at less than the Clausius–Clapeyron rate. Sci. Rep. 6, 3852 (2016).

    Google Scholar 

  56. Hall, A., Cox, P., Huntingford, C. & Klein, S. Progressing emergent constraints on future climate change. Nat. Clim. Change 9, 269–278 (2019).

    Google Scholar 

  57. O’Connor, B. M., Fine, R. A., Maillet, K. A. & Olson, D. B. Formation rates of subtropical underwater in the Pacific Ocean. Deep Sea Res. Part I 49, 1571–1590 (2002).

    Google Scholar 

  58. Sohail, T., Irving, D. B., Zika, J. D., Holmes, R. M. & Church, J. A. Fifty-year trends in global ocean heat content traced to surface heat fluxes in the sub-polar ocean. Geophys. Res. Lett. 48, e2020GL091439 (2021).

    Google Scholar 

  59. Bryden, H. L., Longworth, H. R. & Cunningham, S. A. Slowing of the Atlantic meridional overturning circulation at 25° N. Nature 438, 655–657 (2005).

    CAS  Google Scholar 

  60. Caesar, L., Rahmstorf, S., Robinson, A., Feulner, G. & Saba, V. Observed fingerprint of a weakening Atlantic Ocean overturning circulation. Nature 556, 191–196 (2018).

    CAS  Google Scholar 

  61. Menary, M. B. et al. Aerosol‐forced AMOC changes in CMIP6 historical simulations. Geophys. Res. Lett. 47, e2020GL088166 (2020).

    Google Scholar 

  62. Garuba, O. A. & Klinger, B. A. The role of individual surface flux components in the passive and active ocean heat uptake. J. Clim. 31, 6157–6173 (2018).

    Google Scholar 

  63. Kilbourne, K. H. et al. Atlantic circulation change still uncertain. Nat. Geosci. 15, 165–167 (2022).

    CAS  Google Scholar 

  64. Li, H., Fedorov, A. & Liu, W. AMOC stability and diverging response to Arctic sea ice decline in two climate models. J. Clim. 34, 5443–5460 (2021).

    Google Scholar 

  65. Cheng, L. et al. Past and future ocean warming. Nat. Rev. Earth Environ. 3, 776–794 (2022).

    Google Scholar 

  66. Cai, W. et al. Butterfly effect and a self-modulating El Niño response to global warming. Nature 585, 68–73 (2020).

    CAS  Google Scholar 

  67. Hersbach, H. et al. ERA5 Monthly Averaged Data on Single Levels from 1979 to Present (Copernicus Climate Change Service Climate Data Store, 2019); https://doi.org/10.24381/cds.f17050d7

  68. Liu, H., Wang, P., Jiang, J. & Lin, P. The GPU version of LICOM3 under HIP framework and its large-scale application (updated). Zenodo https://doi.org/10.5281/zenodo.4302813 (2020).

  69. Wei, J. et al. LICOM3-CUDA: a GPU version of LASG/IAP Climate System Ocean Model version 3 based on CUDA. Zenodo https://doi.org/10.5281/zenodo.7440403 (2022).

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Acknowledgements

This research is jointly supported by the National Key R&D Program of China (grant no. 2019YFA0606702), the Strategic Priority Research Program of Chinese Academy of Sciences (grant no. XDB42000000), the Laoshan Laboratory (grant no. LSKJ202202601), the Oceanographic Data Center, Institute of Oceanology, Chinese Academy of Sciences, and the National Natural Science Foundation of China (grant no. NSFC92358302).

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Y. Li and F.W. designed the study. Y. Lu performed the analysis. Y. Lu and Y. Li drafted the paper. All the authors contributed to the interpretation of the results and refinement of the paper.

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Correspondence to Yuanlong Li or Fan Wang.

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Extended data

Extended Data Fig. 1 Changes in freshwater fluxes.

a, Changes of surface net freshwater flux (E-P) for 1965-2018 derived from ERA-5. Upward fluxes are defined as positive. b, Changes of the zonal-mean E-P for the Pacific (blue) and the Atlantic (red). The change is calculated as the difference between the 1999-2018 and 1965-1984 periods. c, changes of 0-800 m mean salinity in CMIP6 MMM. d, Changes of the 0-800 m mean salinity for the Pacific (blue) and the Atlantic (red). e, f, same as c, d, but for E-P. The change in CMIP6 is calculated as the difference between the 1999-2014 and the 1965-1984 periods. In a, c, e, stippling indicates insignificant difference at 90% confidence level based on a two-tailed Student’s t-test.

Extended Data Fig. 2 Regional salinity changes during 1958-2018.

a-d, Changes in 0-800 m salinity of the 45°N-60°N Atlantic, 45°N-60°N Pacific, 0-45°N Atlantic, and 0-45°N Pacific derived from observational data. The blue shadings indicate the spread of IAP, NCEI, and EN4. The gray shadings represent the 1999-2018 and the 1965-1984 periods.

Extended Data Fig. 3 Effects of salinity change on sea level and stratification.

a-c, Changes of basin-mean, 0-800 m steric sea level (SSL) of the NP (blue; 0°-60°N) and NA (red; 0°-60°N) since 1965 (a) and contributions from the temperature (b) and salinity (c) components. The changes based on IAP, NCEI, and EN4 are calculated as the difference between the 1999-2018 and the 1965-1984 periods, while the simulated change by CMIP6 MMM is the difference between the 1999-2014 and the 1965-1984 periods. d-f, As for a-c but for percent change (%) of the 0-800 m ocean stratification (quantified by the squired buoyancy frequency N2) of the NP and NA since 1965 (d) and contributions from the temperature (e) and salinity (f) components. Circles, bars, and error-bars are individual yearly samples, their average, and the 90% confidence interval based on an F-test.

Extended Data Fig. 4 Changes in potential density.

a-c, Total surface density change (a) and the contributions by temperature change (b) and salinity change (c), based on IAP. Stippling indicates insignificant difference at 90% confidence level. The change is calculated as the difference between the 1999-2018 and the 1965-1984 periods.

Extended Data Fig. 5 Changes in surface winds.

a, Climatology wind stress (unit: N m-2; vectors) and wind stress curl (WSC; unit: 10 -7 N m-3; colored) for 1958-2018. b, Change of wind stress (unit: N m-2; vectors) and wind stress curl (WSC; unit: 10 -7 N m-3; colored). The change is calculated as the difference between the 1999-2018 and the 1965-1984 periods. All panels are based on ERA5 data.

Extended Data Fig. 6 Changes of virtual salt flux derived from LICOM3.

a, Changes of the virtual salt flux derived from LICOM3 control experiment. b-e, Same as a but for LICOM3 PRCP, WND, HTFL and reference (REF) experiments, respectively. f, Changes of the 0-2000 m average salinity ΔS derived from LICOM3 REF experiment. The change is calculated as the difference between the 1999-2018 and the 1965-1984 periods. Stippling indicates insignificant difference at 90% confidence level.

Extended Data Fig. 7 Heaving and Spicing modes in LICOM3 simulations.

a-d, Zonal-mean, 0-800 m average ΔS of the NP (blue) and NA (red) in Spicing, derived from CTRL (a), PRCP (b), WND (c), and HTFL (d). ΔS is calculated as the difference of 1999-2018 minus 1965-1984. e-h, As for a-d but for ΔS of the NP and NA in Heaving.

Extended Data Fig. 8 Spatial distributions of NA salinity changes in LICOM3 simulations.

Latitude-depth plots of zonal-mean ΔS of the NA (right) and its Spicing (left) and Heaving (middle) components. ΔS is calculated as the difference of 1999-2018 minus 1965-1984. Stippling indicates insignificant change at 90% confidence level.

Extended Data Fig. 9 Changes of the surface density derived from LICOM3.

a, Surface density changes in CTRL. Stippling indicates insignificant difference at 90% confidence level. The change is calculated as the difference between the 1999-2018 and the 1965-1984 periods. b-d, Same as a but for PRCP (a), WND, and HTFL, respectively.

Extended Data Fig. 10 Changes in the AMOC in LICOM3 simulations.

Anomalies of the AMOC strength relative to the 1958-2018 mean, derived from CTRL, HTFL, WND, and PRCP simulations of LICOM3. The AMOC strength is defined as the maximum meridional overturning stream-function in 300-2000 m over 30°-50°N of the NA.

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Lu, Y., Li, Y., Lin, P. et al. North Atlantic–Pacific salinity contrast enhanced by wind and ocean warming. Nat. Clim. Chang. 14, 723–731 (2024). https://doi.org/10.1038/s41558-024-02033-y

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