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Surprising return of deep convection to the subpolar North Atlantic Ocean in winter 2007–2008

Nature Geoscience volume 2, pages 6772 (2009) | Download Citation

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Abstract

In the process of open-ocean convection in the subpolar North Atlantic Ocean, surface water sinks to depth as a distinct water mass, the characteristics of which affect the meridional overturning circulation and oceanic heat flux. In addition, carbon is sequestered from the atmosphere in the process. In recent years, this convection has been shallow or non-existent, which could be construed as a consequence of a warmer climate. Here we document the return of deep convection to the subpolar gyre in both the Labrador and Irminger seas in the winter of 2007–2008. We use profiling float data from the Argo programme to document deep mixing. Analysis of a variety of in situ, satellite and reanalysis data shows that contrary to expectations the transition to a convective state took place abruptly, without going through a phase of preconditioning. Changes in hemispheric air temperature, storm tracks, the flux of fresh water to the Labrador Sea and the distribution of pack ice all contributed to an enhanced flux of heat from the sea to the air, making the surface water sufficiently cold and dense to initiate deep convection. Given this complexity, we conclude that it will be difficult to predict when deep mixing may occur again.

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References

  1. 1.

    & The formation of Labrador Sea Water. Part 1: Large-scale processes. J. Phys. Oceanogr. 13, 1764–1778 (1983).

  2. 2.

    et al. Investigating the causes of the response of the thermohaline circulation to past and future climate changes. J. Clim. 19, 1365–1387 (2006).

  3. 3.

    et al. The oceanic sink for anthropogenic CO2. Science 305, 367–371 (2004).

  4. 4.

    & The production of North Atlantic Deep Water: Sources, rates and pathways. J. Geophys. Res. 99, 12319–12341 (1994).

  5. 5.

    Quantifying Antarctic bottom water and North Atlantic deep water volumes. J. Geophys. Res. 113, C05027 (2008).

  6. 6.

    Hydrographic changes in the Labrador Sea, 1960–2005. Prog. Oceanogr. 73, 242–276 (2007).

  7. 7.

    , , , & Convection and restratification in the Labrador Sea, 1990–2000. Deep Sea Res. I 49, 1819–1835 (2002).

  8. 8.

    , , & Interannual variability of newly formed Labrador Sea Water from 1994 to 2005. Geophys. Res. Lett. 33, L21S02 (2006).

  9. 9.

    , , & Transformation of the Labrador Sea Water in the subpolar North Atlantic. Geophys. Res. Lett. 34, L22605 (2007).

  10. 10.

    Decadal trends in the North Atlantic Oscillation: Regional temperatures and precipitation. Science 269, 676–679 (1995).

  11. 11.

    , , , & Long-term coordinated changes in the convective activity of the North Atlantic. Prog. Oceanogr. 38, 241–295 (1996).

  12. 12.

    , & Is Labrador Sea Water formed in the Irminger Basin? Deep Sea Res. I 50, 23–52 (2003).

  13. 13.

    et al. Atlantic climate variability and predictability: A CLIVAR perspective. J. Clim. 19, 5100–5121 (2006).

  14. 14.

    , , & North Atlantic winter climate regimes: Spatial asymmetry, stationarity with time, and oceanic forcing. J. Clim. 17, 1055–1068 (2004).

  15. 15.

    , & Variability and renewal of Labrador Sea Water in the Irminger Basin in 1991–2004. J. Geophys. Res. 112, C01006 (2007).

  16. 16.

    & Winter conditions in the Irminger Sea observed with profiling floats. J. Mar. Sci. 62, 313–336 (2004).

  17. 17.

    , & Mid-depth recirculation observed in the interior Labrador and Irminger Seas by direct velocity measurements. Nature 407, 66–69 (2000).

  18. 18.

    & Enhanced production of Labrador Sea Water in 2008. Geophys. Res. Lett. 2008GL036162 (in the press).

  19. 19.

    Winter mixed layer nutrients in the Irminger and Iceland seas, 1990–2000. ICES Mar. Sci. Symp. 219, 329–332 (2003).

  20. 20.

    , & Upper ocean variability between Iceland and Newfoundland, 1993–1998. J. Geophys. Res. 104, 29599–29611 (1999).

  21. 21.

    , & Hydrography of the Labrador Sea during active convection. J. Phys. Oceanogr. 32, 428–457 (2002).

  22. 22.

    , & Observations of open-ocean deep convection in the Labrador Sea from subsurface floats. J. Phys. Oceanogr. 32, 511–526 (2002).

  23. 23.

    & Tip jets and barrier winds: A QuikSCAT climatology of high wind speed events around Greenland. J. Clim. 18, 3713–3725 (2005).

  24. 24.

    , & Atmospheric conditions associated with oceanic convection in the south-east Labrador Sea. Geophys. Res. Lett. 35, L06601 (2008).

  25. 25.

    & Flow response to large-scale topography: The Greenland tip jet. Tellus 51, 728–748 (1999).

  26. 26.

    , , & Winter mixed-layer development in the central Irminger Sea: The effect of strong, intermittent wind events. J. Phys. Oceanogr. 38, 541–565 (2008).

  27. 27.

    , , , & Deep convection in the Irminger Sea forced by the Greenland tip jet. Nature 424, 152–156 (2003).

  28. 28.

    & Decline of subpolar North Atlantic circulation during the 1990s. Science 304, 555–559 (2004).

  29. 29.

    Baffin Bay ice drift and export: 2002–2007. Geophys. Res. Lett. 34, L19501 (2007).

  30. 30.

    , , & What drove the dramatic retreat of Arctic sea ice during summer 2007? Geophys. Res. Lett. 35, L11505 (2008).

  31. 31.

    Oceanographic conditions at Ocean Weather Ship BRAVO, 1964–1974. Atmos. Ocean 18, 227–238 (1980).

  32. 32.

    , , & The ‘Great Salinity Anomaly’ in the northern North Atlantic 1968–1982. Prog. Oceanogr. 20, 103–151 (1988).

  33. 33.

    & Origin and composition of seasonal Labrador Sea freshwater. J. Phys. Oceanogr. 37, 1145–1454 (2007).

  34. 34.

    , & Recent and future changes of the Arctic sea-ice cover. Geophys. Res. Lett. 35, L20503 (2008).

  35. 35.

    , , & GISS analysis of surface temperature change. J. Geophys. Res. 104, 30997–31022 (1999).

  36. 36.

    , & Delayed-mode calibration of autonomous CTD float profiling salinity data by θ-S climatology. J. Atmos. Oceanic Tech. 20, 308–318 (2003).

  37. 37.

    , , & Correction to ‘Recent cooling of the upper ocean’. Geophys. Res. Lett. 34, L16601 (2007).

  38. 38.

    et al. Bulk parameterization of air–sea fluxes: Updates and verification for the COARE algorithm. J. Clim. 16, 571–591 (2003).

  39. 39.

    , & Assessment of composite global sampling: Sea surface wind speed. Geophys. Res. Lett. 33, L17714 (2006).

  40. 40.

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

  41. 41.

    et al. North American regional reanalysis. Bull. Am. Meteorol. Soc. 87, 343–360 (2006).

  42. 42.

    & Objectively analyzed air–sea heat fluxes for the global ice-free oceans (1981–2005). Bull. Am. Meteorol. Soc. 88, 527–539 (2007).

  43. 43.

    & Surface cyclones in the ERA-40 dataset (1958–2001), part I: Novel identification method and global climatology. J. Atmos. Sci. 63, 2486–2507 (2006).

  44. 44.

    et al. The NCEP/NCAR 40-year reanalysis project. Bull. Am. Meteorol. Soc. 77, 437–471 (1996).

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Acknowledgements

The authors wish to thank T. Haine, J. Morison, L. Yu, S. Häkkinen, A. Sarafanov, I. Rigor, R. Kwok, T. Mitchell, H. Stern and O. Martius for valuable suggestions. We thank H. Wernli for providing the cyclone tracking algorithm and R. Goldsmith for developing a Matlab tool to compute and analyse the tracks. J. Hurrell kindly provided the NAO index time series. Argo data were obtained from the GODAE (www.usgodae.org) and Coriolis (www.coriolis.eu.org) data centres. The Sea Winds, OI SST, and NARR and NCEP reanalysis data sets were obtained from the NOAA National Climatic Data Center (www.ncdc.noaa.gov). The AMSR-E data were obtained from the National Snow and Ice Data Center (www.nsidc.org). We thank J. Wang and H. Adiwidjaja for assistance with the reanalysis data. Support for this work was provided by the Ocean Sciences Division of the National Science Foundation.

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Affiliations

  1. Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA

    • Kjetil Våge
    •  & Robert S. Pickart
  2. IFREMER, Laboratoire de Physique des Océans, UMR 6523 CNRS/IFREMER/IRD/UBO, 29280 Plouzané, France

    • Virginie Thierry
  3. Laboratoire d’Océanographie Dynamique et de Climatologie, FR-75252 Paris, France

    • Gilles Reverdin
  4. Applied Physics Laboratory, University of Washington, Seattle, Washington 98105, USA

    • Craig M. Lee
  5. Bedford Institute of Oceanography, Dartmouth, Nova Scotia B2Y 4A2, Canada

    • Brian Petrie
  6. Meteorological Service of Canada, Downsview, Ontario M3H 5T4, Canada

    • Tom A. Agnew
    •  & Amy Wong
  7. Danish Meteorological Institute, DK-2100 Copenhagen, Denmark

    • Mads H. Ribergaard

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Correspondence to Kjetil Våge.

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https://doi.org/10.1038/ngeo382

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