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Seasonal and spatial variations of Southern Ocean diapycnal mixing from Argo profiling floats

Nature Geoscience volume 4, pages 363–366 (2011)Cite this article

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Abstract

The Southern Ocean is thought to be one of the most energetic regions in the world’s oceans. As a result, it is a location of vigorous diapycnal mixing of heat, salt and biogeochemical properties1,2,3. At the same time, the Southern Ocean is poorly sampled, not least because of its harsh climate and remote location. Yet the spatial and temporal variation of diapycnal diffusivity in this region plays an important part in the large-scale ocean circulation and climate4,5,6. Here we use high-resolution hydrographic profiles from Argo floats in combination with the Iridium communications system to investigate diapycnal mixing in the Southern Ocean. We find that the spatial distribution of turbulent diapycnal mixing in the Southern Ocean at depths between 300 and 1,800 m is controlled by the topography, by means of its interaction with the Antarctic Circumpolar Current. The seasonal variation of this mixing can largely be attributed to the seasonal cycle of surface wind stress and is more pronounced in the upper ocean over flat topography. We suggest that additional high-resolution profiles from Argo floats will serve to advance our understanding of mixing processes in the global ocean interior.

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Figure 1: Horizontal distribution of topographic roughness and diapycnal diffusivity in the Southern Ocean.
Figure 2: Depth–longitude distribution of diffusivity, dissipation rate and roughness averaged between 40 and 75° S.
Figure 3: Relation of diapycnal mixing to bottom roughness.
Figure 4: Seasonal changes of diapycnal diffusivity at different depths over different topography.

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Acknowledgements

This work is supported by China National Natural Science Foundation (NSFC) Outstanding Young Investigator Project (40788002), National Key Basic Research Program (2007CB411800), and NSFC Creative Group Project (40921004). We thank the International Argo (Array for Real-time Geostrophic Oceanography) Observational Program for providing data through the open access (http://wo.jcommops.org/cgi-bin/WebObjects/Argo.woa/wa/ptfSearch). Finally, we thank E. Kunze for an insightful explanation about abyssal mixing inferred from lowered ADCP shear and CTD Strain profiles.

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Authors and Affiliations

  1. Physical Oceanography Laboratory, Ocean University of China, Qingdao 266003, China

    Lixin Wu & Zhao Jing

  2. School of Oceanography, University of Washington, Seattle, Washington 98195, USA

    Steve Riser

  3. IFM-GEOMAR, Gebäude Westufer, Düsternbrooker Weg 20, 24105 Kiel, Germany

    Martin Visbeck

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  1. Lixin Wu
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Contributions

L.W. and Z.J. made equal contributions to the paper. L.W. contributed to the central idea and organized the writing of the paper. Z.J. performed the data analysis and contributed to writing of the paper. S.R. and M.V. offered guidance in analyses of the Argo profiling data and mixing, and contributed to the editing of this paper.

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Correspondence to Lixin Wu.

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Wu, L., Jing, Z., Riser, S. et al. Seasonal and spatial variations of Southern Ocean diapycnal mixing from Argo profiling floats. Nature Geosci 4, 363–366 (2011). https://doi.org/10.1038/ngeo1156

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