Letter | Published:

Sea-ice transport driving Southern Ocean salinity and its recent trends

Nature volume 537, pages 8992 (01 September 2016) | Download Citation

Abstract

Recent salinity changes in the Southern Ocean1,2,3,4,5,6,7 are among the most prominent signals of climate change in the global ocean, yet their underlying causes have not been firmly established1,3,4,6. Here we propose that trends in the northward transport of Antarctic sea ice are a major contributor to these changes. Using satellite observations supplemented by sea-ice reconstructions, we estimate that wind-driven8,9 northward freshwater transport by sea ice increased by 20 ± 10 per cent between 1982 and 2008. The strongest and most robust increase occurred in the Pacific sector, coinciding with the largest observed salinity changes4,5. We estimate that the additional freshwater for the entire northern sea-ice edge entails a freshening rate of −0.02 ± 0.01 grams per kilogram per decade in the surface and intermediate waters of the open ocean, similar to the observed freshening1,2,3,4,5. The enhanced rejection of salt near the coast of Antarctica associated with stronger sea-ice export counteracts the freshening of both continental shelf2,10,11 and newly formed bottom waters6 due to increases in glacial meltwater12. Although the data sources underlying our results have substantial uncertainties, regional analyses13 and independent data from an atmospheric reanalysis support our conclusions. Our finding that northward sea-ice freshwater transport is also a key determinant of the mean salinity distribution in the Southern Ocean further underpins the importance of the sea-ice-induced freshwater flux. Through its influence on the density structure of the ocean, this process has critical consequences for the global climate by affecting the exchange of heat, carbon and nutrients between the deep ocean and surface waters14,15,16,17.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

References

  1. 1.

    , & Large-scale freshening of intermediate waters in the Pacific and Indian oceans. Nature 400, 440–443 (1999)

  2. 2.

    , & Freshening of the Ross Sea during the late 20th century. Science 297, 386–389 (2002)

  3. 3.

    , , , & The response of the Antarctic Circumpolar Current to recent climate change. Nat. Geosci. 1, 864–869 (2008)

  4. 4.

    , & Changes in the global hydrological-cycle inferred from ocean salinity. Geophys. Res. Lett. 37, L18701 (2010)

  5. 5.

    , & Ocean salinities reveal strong global water cycle intensification during 1950 to 2000. Science 336, 455–458 (2012)

  6. 6.

    & Antarctic Bottom Water warming and freshening: contributions to sea level rise, ocean freshwater budgets, and global heat gain. J. Clim. 26, 6105–6122 (2013)

  7. 7.

    , , , & Cessation of deep convection in the open Southern Ocean under anthropogenic climate change. Nat. Clim. Change 4, 278–282 (2014)

  8. 8.

    & Wind-driven trends in Antarctic sea-ice drift. Nat. Geosci. 5, 872–875 (2012)

  9. 9.

    , & Anthropogenic influence on recent circulation-driven Antarctic sea ice changes. Geophys. Res. Lett. 41, 8429–8437 (2014)

  10. 10.

    & Large multidecadal salinity trends near the Pacific–Antarctic continental margin. J. Clim. 23, 4508–4524 (2010)

  11. 11.

    , , , & Modeling the spreading of glacial meltwater from the Amundsen and Bellingshausen Seas. Geophys. Res. Lett. 41, 7942–7949 (2014)

  12. 12.

    , & Volume loss from Antarctic ice shelves is accelerating. Science 348, 327–331 (2015)

  13. 13.

    , & Sea ice production and export from coastal polynyas in the Weddell and Ross Seas. Geophys. Res. Lett. 38, L17502 (2011)

  14. 14.

    , & The polar ocean and glacial cycles in atmospheric CO2 concentration. Nature 466, 47–55 (2010)

  15. 15.

    et al. Antarctic sea ice control on ocean circulation in present and glacial climates. Proc. Natl Acad. Sci. USA 111, 8753–8758 (2014)

  16. 16.

    et al. Dominance of the Southern Ocean in anthropogenic carbon and heat uptake in CMIP5 models. J. Clim. 28, 862–886 (2015)

  17. 17.

    et al. The reinvigoration of the Southern Ocean carbon sink. Science 349, 1221–1224 (2015)

  18. 18.

    , , & On the freshening of the northwestern Weddell Sea continental shelf. Ocean Sci. 7, 305–316 (2011)

  19. 19.

    , & On the role of wind-driven sea ice motion on ocean ventilation. J. Phys. Oceanogr. 32, 3376–3395 (2002)

  20. 20.

    & Effects of surface freshwater flux induced by sea ice transport on the global thermohaline circulation. J. Geophys. Res. 108, 3047 (2003)

  21. 21.

    & The effect of the sea ice freshwater flux on Southern Ocean temperatures in CCSM3: deep-ocean warming and delayed surface warming. J. Clim. 24, 2224–2237 (2011)

  22. 22.

    et al. The ERA-Interim reanalysis: configuration and performance of the data assimilation system. Q. J. R. Meteorol. Soc. 137, 553–597 (2011)

  23. 23.

    et al. NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration v. 2, 1980–2009, (National Snow and Ice Data Center, accessed 20 June 2013)

  24. 24.

    & Satellite observations of Antarctic sea ice thickness and volume. J. Geophys. Res. 117, C08025 (2012)

  25. 25.

    et al. A model reconstruction of the Antarctic sea ice thickness and volume changes over 1980–2008 using data assimilation. Ocean Model. 64, 67–75 (2013)

  26. 26.

    , & Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors v. 2, 1980–2009 (National Snow and Ice Data Center, accessed 14 April 2014)

  27. 27.

    et al. Water-mass transformation by sea ice in the upper branch of the Southern Ocean overturning. Nat. Geosci. 9, 596–601 (2016)

  28. 28.

    Closure of the global overturning circulation through the Indian, Pacific, and Southern Oceans: schematics and transports. Oceanography 26, 80–97 (2013)

  29. 29.

    , , & Estimation of surface heat/salt fluxes associated with sea ice growth/melt in the Southern Ocean. Sci. Online Lett. Atmos. 7, 17–20 (2011)

  30. 30.

    et al. Snow on Antarctic sea ice. Rev. Geophys. 39, 413–445 (2001)

  31. 31.

    & Antarctic sea ice variability and trends, 1979–2006. J. Geophys. Res. 113, C07004 (2008)

  32. 32.

    Characteristics of Arctic winter sea ice from satellite multispectral microwave observations. J. Geophys. Res. 91, 975–994 (1986)

  33. 33.

    et al. Thickness distribution of Antarctic sea ice. J. Geophys. Res. 113, C05S92 (2008)

  34. 34.

    , , & A comparison of satellite-derived sea-ice motion with drifting-buoy data in the Weddell Sea, Antarctica. Ann. Glaciol. 52, 103–110 (2011)

  35. 35.

    , , , & Sea ice motion from satellite passive microwave imagery assessed with ERS SAR and buoy motions. J. Geophys. Res. 103, 8191–8214 (1998)

  36. 36.

    Ross sea ice motion, area flux, and deformation. J. Clim. 18, 3759–3776 (2005)

  37. 37.

    Climate Data Operators v. 1.6.8. (CDO, 2015);

  38. 38.

    , , & Passive microwave algorithms for sea ice concentration: A comparison of two techniques. Remote Sens. Environ. 60, 357–384 (1997)

  39. 39.

    , & A spurious jump in the satellite record: has Antarctic sea ice expansion been overestimated? Cryosphere 8, 1289–1296 (2014)

  40. 40.

    & Uncertainties in Antarctic sea-ice thickness retrieval from ICESat. Ann. Glaciol. 56, 107–119 (2015)

  41. 41.

    & Snow depth of the Weddell and Bellingshausen sea ice covers from IceBridge surveys in 2010 and 2011: an examination. J. Geophys. Res. 119, 4141–4167 (2014)

  42. 42.

    et al. Thick and deformed Antarctic sea ice mapped with autonomous underwater vehicles. Nat. Geosci. 8, 61–67 (2015)

  43. 43.

    , & ICESat observations of seasonal and interannual variations of sea-ice freeboard and estimated thickness in the Weddell Sea, Antarctica (2003-2009). Ann. Glaciol. 52, 43–51 (2011)

  44. 44.

    , & Antarctic sea-ice thickness retrieval from ICESat: Inter-comparison of different approaches. Remote Sens. 8, 538 (2016)

  45. 45.

    & Antarctic sea ice thickness and snow-to-ice conversion from atmospheric reanalysis and passive microwave snow depth. J. Geophys. Res. 113, C02S12 (2008)

  46. 46.

    Modeling the impact of wind intensification on Antarctic sea ice volume. J. Clim. 27, 202–214 (2014)

  47. 47.

    et al. Modeled trends in Antarctic sea ice thickness. J. Clim. 27, 3784–3801 (2014)

  48. 48.

    , & in Oceanographic Applications of Remote Sensing (eds & ) 367–379 (CRC Press, 1995)

  49. 49.

    , & Satellite-derived maps of Arctic and Antarctic sea ice motion: 1988 to 1994. Geophys. Res. Lett. 24, 897–900 (1997)

  50. 50.

    et al. AVHRR-based Polar Pathfinder products for modeling applications. Ann. Glaciol. 25, 388–392 (1997)

  51. 51.

    , , , & A comparison of East Antartic sea-ice motion derived using drifting buoys and remote sensing. Ann. Glaciol. 33, 139–144 (2001)

  52. 52.

    et al. An intercomparison of Arctic ice drift products to deduce uncertainty estimates. J. Geophys. Res. 119, 4887–4921 (2014)

  53. 53.

    Dynamical Interaction Between Atmosphere and Sea Ice In Antarctica. MSc thesis, Utrecht University (2011)

  54. 54.

    , , , & Freshening and dense shelf water reduction in the Okhotsk Sea linked with sea ice decline. Prog. Oceanogr. 126, 71–79 (2014)

  55. 55.

    & A review of sea ice density. Cold Reg. Sci. Technol. 24, 1–6 (1996)

  56. 56.

    , & Simulating the mass balance and salinity of Arctic and Antarctic sea ice. 2: importance of sea ice salinity variations. Ocean Model. 27, 54–69 (2009)

  57. 57.

    & Drivers of variability in Arctic sea-ice drift speed. J. Geophys. Res. 119, 5755–5775 (2014)

  58. 58.

    User’s Manual: SSM/I Antenna Temperature Tapes Revision 1. Report No. 120191 (Remote Sensing Systems, 1991)

  59. 59.

    & Sea ice motion in response to geostrophic winds. J. Geophys. Res. 87, 5845–5852 (1982)

  60. 60.

    Sea ice motion in response to surface wind and ocean current in the Southern Ocean. J. Meteorol. Soc. Jpn 82, 1223–1231 (2004)

  61. 61.

    et al. Homogeneity adjustments of in situ atmospheric climate data: a review. Int. J. Climatol. 18, 1493–1517 (1998)

  62. 62.

    , , , & Guidelines on Climate Metadata and Homogenization. Report No. WCDMP-53 (World Meteorological Organization, 2003)

  63. 63.

    et al. Statistical significance of trends and trend differences in layer-average atmospheric temperature time series. J. Geophys. Res. 105, 7337–7356 (2000)

  64. 64.

    , & Mapping of sea ice production for Antarctic coastal polynyas. Geophys. Res. Lett. 35, L07606 (2008)

  65. 65.

    et al. Antarctic Bottom Water production by intense sea-ice formation in the Cape Darnley polynya. Nat. Geosci. 6, 235–240 (2013)

  66. 66.

    , , & Variability and trends in sea ice extent and ice production in the Ross Sea. J. Geophys. Res. 116, C04021 (2011)

  67. 67.

    , & The areas and ice production of the western and central Ross Sea polynyas, 1992-2002, and their relation to the B-15 and C-19 iceberg events of 2000 and 2002. J. Mar. Syst. 68, 201–214 (2007)

  68. 68.

    & Variability of dense water formation in the Ross Sea. Ocean Dyn. 55, 68–87 (2005)

  69. 69.

    , & The role of sea ice in the fresh-water budget of the Weddell Sea, Antarctica. Ann. Glaciol. 33, 419–424 (2001)

  70. 70.

    , & Sea ice transports in the Weddell Sea. J. Geophys. Res. 106, 9057–9073 (2001)

  71. 71.

    & Atmospheric and oceanic forcing of Weddell Sea ice motion. J. Geophys. Res. 101, 20809–20824 (1996)

  72. 72.

    & Quality control of ocean temperature and salinity profiles — Historical and real-time data. J. Mar. Syst. 65, 158–175 (2007)

  73. 73.

    , & The mixed layer salinity budget and sea ice in the Southern Ocean. J. Geophys. Res. 116, C08031 (2011)

  74. 74.

    Bottom water production and its links with the thermohaline circulation. Antarct. Sci. 16, 427–437 (2004)

  75. 75.

    et al. Calving fluxes and basal melt rates of Antarctic ice shelves. Nature 502, 89–92 (2013)

  76. 76.

    , & Contribution of giant icebergs to the Southern Ocean freshwater flux. J. Geophys. Res. 111, C03004 (2006)

  77. 77.

    , & in Oceanology of the Antarctic Continental Shelf (ed. ) 59–85 (American Geophysical Union, 1985)

  78. 78.

    et al. Changes in the freshwater composition of the upper ocean west of the Antarctic Peninsula during the first decade of the 21st century. Prog. Oceanogr. 87, 127–143 (2010)

  79. 79.

    , & On the meridional extent and fronts of the Antarctic Circumpolar Current. Deep. Res. I 42, 641–673 (1995)

  80. 80.

    , , & The mechanism for Antarctic Intermediate Water renewal in a world ocean model. J. Phys. Oceanogr. 23, 1553–1560 (1993)

  81. 81.

    in The South Atlantic: Present and Past Circulation (eds et al. .) 219–238 (Springer, 1996)

  82. 82.

    , , & An exchange window for the injection of Antarctic Intermediate Water into the South Pacific. J. Phys. Oceanogr. 37, 31–49 (2007)

  83. 83.

    & Circulation, renewal, and modification of Antarctic Mode and Intermediate Water. J. Phys. Oceanogr. 31, 1005–1030 (2001)

  84. 84.

    et al. Formation rates of Subantarctic mode water and Antarctic intermediate water within the South Pacific. Deep. Res. I 58, 524–534 (2011)

  85. 85.

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

Download references

Acknowledgements

This work was supported by ETH Research Grant CH2-01 11-1 and by European Union (EU) grant 264879 (CARBOCHANGE). I.F. was supported by C2SM at ETH Zürich and the Swiss National Science Foundation Grant P2EZP2-152133. S.K. was supported by the Center of Excellence for Climate System Analysis and Prediction (CliSAP), University of Hamburg, Germany. F.A.H. and S.K. acknowledge support from the International Space Science Institute (ISSI), Bern, Switzerland, under project #245. We are thankful to F. Massonnet for providing the sea-ice thickness reconstruction and discussion. The ICESat-1 sea-ice thickness data were provided by the NASA Goddard Space Flight Center. The ship-based sea-ice thickness data were provided by the SCAR Antarctic Sea Ice Processes and Climate (ASPeCt) programme. We appreciate the provision of sea-ice concentration and motion data by the National Snow and Ice Data Center, the Integrated Climate Data Center at the University of Hamburg and R. Kwok. We thank T. Frölicher, S. Yang, A. Stössel, M. Frischknecht, L. Papritz, P. Durack, M. van den Broecke, J. Lenaerts, J. van Angelen and M. Meredith for discussion, comments, and ideas.

Author information

Affiliations

  1. Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland

    • F. Alexander Haumann
    • , Nicolas Gruber
    • , Matthias Münnich
    •  & Ivy Frenger
  2. Center for Climate Systems Modeling, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland

    • F. Alexander Haumann
    •  & Nicolas Gruber
  3. Biogeochemical Modelling, GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany

    • Ivy Frenger
  4. Integrated Climate Data Center (ICDC), Center for Earth System Research and Sustainability, University of Hamburg, Hamburg, Germany.

    • Stefan Kern

Authors

  1. Search for F. Alexander Haumann in:

  2. Search for Nicolas Gruber in:

  3. Search for Matthias Münnich in:

  4. Search for Ivy Frenger in:

  5. Search for Stefan Kern in:

Contributions

F.A.H., M.M. and I.F. conceived the study. F.A.H. collated the data and performed the analyses. F.A.H. and N.G. wrote the manuscript. M.M., I.F. and S.K. assisted during the writing process. S.K. assisted in the quality and uncertainty assessment. All authors developed the methods and interpreted the results. N.G. and M.M. supervised this study.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to F. Alexander Haumann.

Reviewer Information Nature thanks K. Ohshima and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Extended data

About this article

Publication history

Received

Accepted

Published

DOI

https://doi.org/10.1038/nature19101

Further reading

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.