Abstract
Despite the central role of the oceans in the global hydrological cycle, direct observations of precipitation over the oceans are too sparse to infer global patterns of variability. For the regions of water-mass formation (the high latitudes), however, it is possible to obtain indirect information on changes in the surface salinity budget from salinity measurements elsewhere, as water masses in the ocean carry distinct signatures in temperature and salinity over long distances. Here we present a comparison of historical hydrographic data collected between 1930 and 19801,2 with six more-recent trans-oceanic hydrographic sections (1985–94) fromthe intermediate waters of the Pacific and Indian oceans3,4. North Pacific Intermediate Water and Antarctic Intermediate Water both show coherent basin-wide salinity decreases with time. The simplest explanation for these changes is a freshening of surface waters, over approximately 22 years, in the high-latitude North Pacific and Southern oceans, suggesting that precipitation (minus evaporation) has increased over the polar gyres. We estimate an increase by about 31 mm yr−1 for the Southern Ocean (between 55° S and 65° S), which is about three times larger than the values suggested by coupled atmosphere–ocean models with increasing atmospheric greenhouse-gas concentrations for the same period5,6,7,8. The patterns of change are, however, qualitatively consistent between models and observations, and our results provide evidence for an intensification of the global hydrological cycle over the past decades.
This is a preview of subscription content, access via your institution
Access options
Subscribe to this journal
Receive 51 print issues and online access
$199.00 per year
only $3.90 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
Gordon, A., Molinelli, E. J. & Baker, T. N. Southern Ocean Atlas (Alfred Wegener Inst. Amerind, New Delhi, (1982).
World Ocean Atlas 1994: CD-ROM data set (Natl Oceanographic Data Center, Ocean Climate Lab., Washington DC, (1994).
WOCE Data Products Committee WOCE Global Data, Version1. CD-ROM; WOCE Rep. 158/98 CD-ROM (WOCE Int. Project Office, Southampton, UK, (1998).
WOCE Hydrographic Program Office WOCE Hydrographic Program Data (Scripps Inst. of Oceanography, SanDieg, (1998); also available at 〈http://whpo.ucsd.edu〉 (cited 31 Aug. (1998).
Manabe, S., Bryan, K. & Spelman, M. J. Transient response of a global ocean-atmosphere model to a doubling of atmospheric carbon dioxide. J. Phys. Oceanogr. 20, 722–749 (1990).
Gordon, H. B. & O'Farrell, S. P. Transient climate change in the CSIRO coupled model with dynamic sea ice. Mon. Weath. Rev. 125, 875–907 (1997).
Manabe, S., Stouffer, R. J., Spelman, M. J. & Bryan, K. Transient responses of a coupled ocean-atmosphere model to gradual changes of atmospheric CO2. Part I: annual mean response. J. Clim. 4, 785–818 (1991).
Murphy, J. M. & Mitchell, J. F. B. Transient response of the Hadley Centre coupled ocean-atmosphere model to increasing carbon dioxide. Part II: Spatial and temporal structure of response. J. Clim. 8, 57–80 (1995).
Levitus, S. Interpentadal variability of temperature and salinity at intermediate depths of the North Atlantic Ocean, 1970–1974 versus 1955–1959. J. Geophys. Res. 94, 6091–6131 (1989).
Bryden, H. L.et al. Decadal changes in water mass characteristics at 24N in the subtropical North Atlantic Ocean. J. Clim. 9, 3162–3186 (1996).
Dickson, R., Lazier, J., Meincke, J., Rhines, P. & Swift, J. Long-term coordinated changes in the convective activity of the North Atlantic. Prog. Oceanogr. 38, 241–295 (1996).
Read, J. F. & Gould, W. J. Cooling and freshening of the subpolar North Atlantic Ocean since the 1960s. Nature 360, 55–57 (1992).
Bindoff, N. L. & Church, J. A. Warming of the water column in the southwest Pacific Ocean. Nature 357, 59–62 (1992).
Johnson, G. C. & Orsi, A. H. Southwest Pacific Ocean water mass changes between 1968/9 and 1990/1. J. Clim. 10, 306–316 (1997).
Joyce, T. M., Luyten, J. R., Kubryakov, A., Bahr, F. B. & Pallant, J. S. Meso- to large-scale structure of subducting water in the subtropical gyre of the eastern North Atlantic Ocean. J. Phys. Oceanogr. 28, 40–61 (1998).
Hazeleger, W. & Drijfhout, S. S. Mode water variability in a model of the subtropical gyre: response to anomalous forcing. J. Phys. Oceanogr. 28, 266–288 (1998).
Hazeleger, W. & Drijfhout, S. S. Stochastically forced Mode Water variability. J. Phys. Oceanogr. (in the press).
Bindoff, N. L. & McDougall, T. J. Diagnosing climate change and ocean ventilation using hydrographic data. J. Phys. Oceanogr. 24, 1137–1152 (1994).
Warner, M. J., Bullister, J. L., Wisegarver, D. P., Gammon, R. H. & Wiess, R. F. Basin-wide distributions of chlorofluorocarbons CFC-11 and CFC-12 in the North Pacific: 1985–1989. J. Geophys. Res. 101, 20525–20542 (1996).
McCartney, M. S. in A Voyage of Discovery (ed. Angel, M.) 103–119 (Pergamon, Oxford, (1977).
Reid, J. L. On the total geostrophic circulation of the South Pacific Ocean: flow patterns, tracers and transports. Prog. Oceanogr. 16, 1–61 (1986).
Morgan, V. I., Goodwin, I. D., Etheridge, D. M. & Wookey, C. W. Evidence from Antarctic ice cores for recent increases in snow accumulation. Nature 354, 58–60 (1991).
White, W. B. & Peterson, R. G. An Antarctic circumpolar wave in surface pressure, wind, temperature, and sea-ice extent. Nature 380, 699–702 (1996).
Hurrel, J. W. & Loon, H. V. Amodulation of the atmospheric annual cycle in the Southern Hemisphere. Tellus A 46, 325–338 (1994).
Reid, J. & Mantyla, A. World Dataset (cited Jan. 1999) 〈ftp://minerva.ucsd.edu〉 (1995).
Jackett, D. & McDougall, T. J. Aneutral density variable for the world's oceans. J. Phys. Oceanogr. 27, 237–263 (1997).
Bindoff, N. L. & Wunsch, C. Comparison of synoptic and climatologically mapped sections in the South Pacific Ocean. J. Clim. 5, 631–645 (1992).
Lozier, M. S., McCarteney, M. S. & Owens, W. B. Anomalous anomalies in averaged hydrographic data. J. Phys. Oceanogr. 24, 2624–2638 (1994).
Church, J. A., Godfrey, J. S., Jackett, D. R. & McDougall, T. J. Amodel of sea level rise caused by ocean thermal expansion. J. Clim. 4, 438–456 (1991).
Levitus, S. Climatological Atlas of the World Ocean (Natl Oceanographic and Atmospheric Administration, US Dept of Commerce, Washington DC, (1982).
Acknowledgements
We thank H. Bryden for access to the WOCE P21 section at 17° S before publication, and R. Dickson for discussions about changes in the semi-annual oscillation. A.W. was supported by a National Greenhouse Advisory Committee scholarship. This Letter is a contribution to the World Ocean Circulation Experiment and the CSIRO Climate Change Research Program.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Wong, A., Bindoff, N. & Church, J. Large-scale freshening of intermediate waters in the Pacific and Indian oceans. Nature 400, 440–443 (1999). https://doi.org/10.1038/22733
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1038/22733
This article is cited by
-
Seasonal and spatial variations in spice generation in the South Indian Ocean salinity maxima
Ocean Dynamics (2022)
-
Multi-decadal changes in the South China Sea mixed layer salinity
Climate Dynamics (2021)
-
Rapid freshening of Japan Sea Intermediate Water in the 2010s
Journal of Oceanography (2021)
-
Temperature and salinity variability at intermediate depths in the western equatorial Pacific revealed by TRITON buoy data
Journal of Oceanography (2020)
-
Previously unidentified Indonesian Throughflow pathways and freshening in the Indian Ocean during recent decades
Scientific Reports (2019)
Comments
By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.