Increased risk of a shutdown of ocean convection posed by warm North Atlantic summers

Abstract

A shutdown of ocean convection in the subpolar North Atlantic, triggered by enhanced melting over Greenland, is regarded as a potential transition point into a fundamentally different climate regime1,2,3. Noting that a key uncertainty for future convection resides in the relative importance of melting in summer and atmospheric forcing in winter, we investigate the extent to which summer conditions constrain convection with a comprehensive dataset, including hydrographic records that are over a decade in length from the convection regions. We find that warm and fresh summers, characterized by increased sea surface temperatures, freshwater concentrations and melting, are accompanied by reduced heat and buoyancy losses in winter, which entail a longer persistence of the freshwater near the surface and contribute to delaying convection. By shortening the time span for the convective freshwater export, the identified seasonal dynamics introduce a potentially critical threshold that is crossed when substantial amounts of freshwater from one summer are carried over into the next and accumulate. Warm and fresh summers in the Irminger Sea are followed by particularly short convection periods. We estimate that in the winter 2010–2011, after the warmest and freshest Irminger Sea summer on our record, ~40% of the surface freshwater was retained.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Labrador Sea, 2010–2011.
Fig. 2: Fresh summers in the Irminger Sea.
Fig. 3: Summer constraints on hydrographic evolution in the Labrador Sea.
Fig. 4: Summer constraints on atmospheric evolution in autumn and winter.
Fig. 5: Trends in the forcing parameters, 1990–2014.

References

  1. 1.

    Clark, P. U., Pisias, N. G., Stocker, T. F. & Weaver, A. J. The role of the thermohaline circulation in abrupt climate change. Nature 415, 863–869 (2002).

    CAS  Article  Google Scholar 

  2. 2.

    Rahmstorf, S. Ocean circulation and climate during the past 120,000 years. Nature 419, 207–214 (2002).

    CAS  Article  Google Scholar 

  3. 3.

    Lenton, T. M. et al. Tipping elements in the Earth’s climate system. Proc. Natl Acad. Sci. USA 105, 1786–1793 (2008).

    CAS  Article  Google Scholar 

  4. 4.

    Lozier, M. S. Overturning in the North Atlantic. Annu. Rev. Mar. Sci. 4, 291–315 (2012).

    Article  Google Scholar 

  5. 5.

    Trenberth, K. E. & Caron, J. M. Estimates of meridional atmosphere and ocean heat transports. J. Clim. 14, 3433–3443 (2001).

    Article  Google Scholar 

  6. 6.

    Bamber, J., den Broeke, M., Ettema, J., Lenaerts, J. & Rignot, E. Recent large increases in freshwater fluxes from Greenland into the North Atlantic. Geophys. Res. Lett. 39, L19501 (2012).

    Article  Google Scholar 

  7. 7.

    Mernild, S. H. et al. Freshwater flux to Sermilik Fjord, SE Greenland. The Cryosphere 4, 453–465 (2010).

    Article  Google Scholar 

  8. 8.

    Pickart, R. S., Straneo, F. & Moore, G. W. K. Is Labrador Sea water formed in the Irminger Basin? Deep Sea Res. I Oceanogr. Res. Pap. 50, 23–52 (2003).

    Article  Google Scholar 

  9. 9.

    Våge, K. et al. The Irminger Gyre: circulation, convection, and interannual variability. Deep Sea Res. I Oceanogr. Res. Pap. 58, 590–614 (2011).

    Article  Google Scholar 

  10. 10.

    Lavender, K. L., Davis, R. E. & Owens, W. B. Observations of open-ocean deep convection in the Labrador Sea from subsurface floats. J. Phys. Oceanogr. 32, 511–526 (2002).

    Article  Google Scholar 

  11. 11.

    Pickart, R. S., Torres, D. J. & Clarke, R. A. Hydrography of the Labrador Sea during active convection. J. Phys. Oceanogr. 32, 428–457 (2002).

    Article  Google Scholar 

  12. 12.

    Hurrell, J. W., Kushnir, Y., Ottersen, G. & Visbeck, M. in The North Atlantic Oscillation: Climatic Significance and Environmental Impact 1–35 (American Geophysical Union, Washington, DC, USA, 2003).

  13. 13.

    Hanna, E. et al. Atmospheric and oceanic climate forcing of the exceptional Greenland ice sheet surface melt in summer 2012. Int. J. Climatol. 34, 1022–1037 (2014).

    Article  Google Scholar 

  14. 14.

    Lazier, J., Hendry, R., Clarke, A., Yashayaev, I. & Rhines, P. Convection and restratification in the Labrador Sea, 1990–2000. Deep Sea Res. I Oceanogr. Res. Pap. 49, 1819–1835 (2002).

    CAS  Article  Google Scholar 

  15. 15.

    Gill, A. E. AtmosphereOcean Dynamics (International Geophysics Series) (Academic Press, San Diego, CA, USA, 1982).

  16. 16.

    Ferreira, D. & Frankignoul, C. The transient atmospheric response to midlatitude SST anomalies. J. Clim. 18, 1049–1067 (2005).

    Article  Google Scholar 

  17. 17.

    Deser, C., Tomas, R. A. & Peng, S. The transient atmospheric circulation response to North Atlantic SST and sea ice anomalies. J. Clim. 20, 4751–4767 (2007).

    Article  Google Scholar 

  18. 18.

    Czaja, A. & Frankignoul, C. Observed impact of Atlantic SST anomalies on the North Atlantic oscillation. J. Clim. 15, 606–623 (2002).

    Article  Google Scholar 

  19. 19.

    Gastineau, G., D’Andrea, F. & Frankignoul, C. Atmospheric response to the North Atlantic Ocean variability on seasonal to decadal time scales. Clim. Dyn. 40, 2311–2330 (2013).

    Article  Google Scholar 

  20. 20.

    Gastineau, G., L’Hévéder, B., Codron, F. & Frankignoul, C. Mechanisms determining the winter atmospheric response to the Atlantic overturning circulation. J. Clim. 29, 3767–3785 (2016).

    Article  Google Scholar 

  21. 21.

    Cassou, C., Deser, C. & Alexander, M. A. Investigating the impact of reemerging sea surface temperature anomalies on the winter atmospheric circulation over the North Atlantic. J. Clim. 20, 3510–3526 (2007).

    Article  Google Scholar 

  22. 22.

    Fröb, F. et al. Irminger Sea deep convection injects oxygen and anthropogenic carbon to the ocean interior. Nat. Commun. 7, 13244 (2016).

    Article  Google Scholar 

  23. 23.

    De Jong, M. F. & de Steur, L. Strong winter cooling over the Irminger Sea in winter 2014–2015, exceptional deep convection, and the emergence of anomalously low SST. Geophys. Res. Lett. 43, 7106–7113 (2016).

    Article  Google Scholar 

  24. 24.

    Yashayaev, I. & Loder, J. W. Further intensification of deep convection in the Labrador Sea in 2016. Geophys. Res. Lett. 44, 1429–1438 (2017).

    Article  Google Scholar 

  25. 25.

    Hanna, E., Cropper, T. E., Hall, R. J. & Cappelen, J. Greenland Blocking Index 1851–2015: a regional climate change signal. Int. J. Climatol. 36, 4847–4861 (2016).

    Article  Google Scholar 

  26. 26.

    Straneo, F. Heat and freshwater transport through the central Labrador Sea. J. Phys. Oceanogr. 36, 606–628 (2006).

    Article  Google Scholar 

  27. 27.

    Fan, X., Send, U., Testor, P., Karstensen, J. & Lherminier, P. Observations of Irminger Sea anticyclonic eddies. J. Phys. Oceanogr. 43, 805–823 (2013).

    Article  Google Scholar 

  28. 28.

    IPCC Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) (Cambridge Univ. Press, 2014).

  29. 29.

    Gentemann, C. L., Meissner, T. & Wentz, F. J. Accuracy of satellite sea surface temperatures at 7 and 11 GHz. IEEE Trans. Geosci. Remote Sens. 48, 1009–1018 (2010).

    Article  Google Scholar 

  30. 30.

    Reynolds, R. W. et al. Daily high-resolution-blended analyses for sea surface temperature. J. Clim. 20, 5473–5496 (2007).

    Article  Google Scholar 

  31. 31.

    Rayner, N. A. et al. Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res. Atmos. 108, 4407 (2003).

    Article  Google Scholar 

  32. 32.

    Le Traon, P. Y., Nadal, F. & Ducet, N. An improved mapping method of multisatellite altimeter data. J. Atmos. Ocean. Technol. 15, 522–534 (1998).

    Article  Google Scholar 

  33. 33.

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

    Article  Google Scholar 

  34. 34.

    Mote, T. L. et al. Greenland surface melt trends 1973–2007: evidence of a large increase in 2007. Geophys. Res. Lett. 34, L22507 (2007).

    Article  Google Scholar 

Download references

Acknowledgements

We thank the staff at the NOAA/OAR/ESRL, NCAR and Hadley Centre for providing the SST data, and the staff at Ssalto/Duacs, Aviso and CNES for producing and distributing the altimeter products. We also appreciate the efforts that went into the development and management of the Ocean Observatories Initiative. The research in this study contributes to the projects ‘Blue-Action’ and ‘AtlantOS’ and was funded by the EU Horizon 2020 Programme under grant agreements 727852 and 633211. It was further supported by the German Federal Ministry of Education and Research as part of the ‘Regional Atlantic Circulation and Global Change’ project.

Author information

Affiliations

Authors

Contributions

J.F. and J.K. were involved in planning, acquiring and processing the mooring data. M.O. and J.K. conceived the story. M.O. carried out the data analysis and interpreted the results. All authors contributed to writing the paper.

Corresponding author

Correspondence to Marilena Oltmanns.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figures 1–9, Supplementary Table 1 and Supplementary References

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Oltmanns, M., Karstensen, J. & Fischer, J. Increased risk of a shutdown of ocean convection posed by warm North Atlantic summers. Nature Clim Change 8, 300–304 (2018). https://doi.org/10.1038/s41558-018-0105-1

Download citation

Search

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing