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Surface-water iron supplies in the Southern Ocean sustained by deep winter mixing

Abstract

Low levels of iron limit primary productivity across much of the Southern Ocean. At the basin scale, most dissolved iron is supplied to surface waters from subsurface reservoirs, because land inputs are spatially limited. Deep mixing in winter together with year-round diffusion across density surfaces, known as diapycnal diffusion, are the main physical processes that carry iron-laden subsurface waters to the surface. Here, we analyse data on dissolved iron concentrations in the top 1,000 m of the Southern Ocean, taken from all known and available cruises to date, together with hydrographic data to determine the relative importance of deep winter mixing and diapycnal diffusion to dissolved iron fluxes at the basin scale. Using information on the vertical distribution of iron we show that deep winter mixing supplies ten times more iron to the surface ocean each year, on average, than diapycnal diffusion. Biological observations from the sub-Antarctic sector suggest that following the depletion of this wintertime iron pulse, intense iron recycling sustains productivity over the subsequent spring and summer. We conclude that winter mixing and surface-water iron recycling are important drivers of temporal variations in Southern Ocean primary production.

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Figure 1: Depths and potential density of the ferricline and its seasonal evolution.
Figure 2: The relationship between the ferricline and mixed-layer depths and calculations of physically mediated iron fluxes.
Figure 3: Assessments of how different physically mediated iron supply mechanisms compare to utilization and their contribution to total iron fluxes.
Figure 4: A schematic representation of the seasonal variability in Southern Ocean Fe cycling.

References

  1. Boyd, P. W. & Ellwood, M. J. The biogeochemical cycle of iron in the ocean. Nature Geosci. 3, 675–682 (2010).

    Article  Google Scholar 

  2. Moore, C. M. et al. Processes and patterns of oceanic nutrient limitation. Nature Geosci. 6, 701–710 (2013).

    Article  Google Scholar 

  3. Sarmiento, J. L., Hughes, T. M. C., Stouffer, R. J. & Manabe, S. Simulated response of the ocean carbon cycle to anthropogenic climate warming. Nature 393, 245–249 (1998).

    Article  Google Scholar 

  4. Takahashi, T. et al. Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans. Deep-Sea Res. II 56, 554–577 (2009).

    Article  Google Scholar 

  5. Boyd, P. W. et al. Climate-mediated changes to mixed-layer properties in the Southern Ocean: Assessing the phytoplankton response. Biogeosciences 5, 847–864 (2008).

    Article  Google Scholar 

  6. Tagliabue, A. et al. A global compilation of dissolved iron measurements: Focus on distributions and processes in the Southern Ocean. Biogeosciences 9, 2333–2349 (2012).

    Article  Google Scholar 

  7. Boyd, P. W., Arrigo, K. R., Strzepek, R. & van Dijken, G. L. Mapping phytoplankton iron utilization: Insights into Southern Ocean supply mechanisms. J. Geophys. Res. 117, C06009 (2012).

    Article  Google Scholar 

  8. Tagliabue, A. et al. Hydrothermal contribution to the oceanic dissolved iron inventory. Nature Geosci. 3, 252–256 (2010).

    Article  Google Scholar 

  9. Boyd, P. W., Ibisanmi, E., Sander, S. G., Hunter, K. A. & Jackson, G. A. Remineralization of upper ocean particles: Implications for iron biogeochemistry. Limnol. Oceanogr. 55, 1271–1288 (2010).

    Article  Google Scholar 

  10. Moore, J. K., Doney, S. C., Glover, D. M. & Fung, I. Y. Iron cycling and nutrient-limitation patterns in surface waters of the World Ocean. Deep-Sea Res. 49, 463–507 (2002).

    Article  Google Scholar 

  11. Watson, A. J. in The Biogeochemical Cycle of Iron in Seawater (eds Turner, Keith David R. & Hunter, A.) (John Wiley, (2001) Ch. 2

    Google Scholar 

  12. De Baar, H. J. W. et al. Importance of iron for plankton blooms and carbon-dioxide drawdown in the Southern-Ocean. Nature 373, 412–415 (1995).

    Article  Google Scholar 

  13. Toggweiler, J. R. & Russell, J. Ocean circulation in a warming climate. Nature 451, 286–288 (2008).

    Article  Google Scholar 

  14. Boyd, P. W. et al. Microbial control of diatom bloom dynamics in the open ocean. Geophys. Res. Lett. 39, L18601 (2012).

    Article  Google Scholar 

  15. Frew, R. D. et al. Particulate iron dynamics during FeCycle in subantarctic waters southeast of New Zealand. Glob. Biogeochem. Cycles 20, GB1S93 (2006).

    Article  Google Scholar 

  16. Bowie, A. R. et al. Biogeochemical iron budgets of the Southern Ocean south of Australia: Decoupling of iron and nutrient cycles in the subantarctic zone by the summertime supply. Glob. Biogeochem. Cycles 23, GB4034 (2009).

    Article  Google Scholar 

  17. Boyd, P. W. et al. FeCycle: Attempting an iron biogeochemical budget from a mesoscale SF6 tracer experiment in unperturbed low iron waters. Glob. Biogeochem. Cycles 19, GB4S20 (2005).

    Article  Google Scholar 

  18. Croot, P. L. et al. Physical mixing effects on iron biogeochemical cycling: FeCycle experiment. J. Geophys. Res. 112, C06015 (2007).

    Article  Google Scholar 

  19. Johnson, K. S., Gordon, R. M. & Coale, K. H. What controls dissolved iron concentrations in the world ocean?. Mar. Chem. 57, 137–161 (1997).

    Article  Google Scholar 

  20. Sallée, J-B., Speer, K., Rintoul, S. & Wijffels, S. Southern Ocean thermocline ventilation. J. Phys. Oceanogr. 40, 509–529 (2010).

    Article  Google Scholar 

  21. Law, C. S. Vertical eddy diffusion and nutrient supply to the surface mixed layer of the Antarctic Circumpolar Current. J. Geophys. Res. 108, 3272 (2003).

    Article  Google Scholar 

  22. Cisewski, B., Strass, V. H. & Prandke, H. Upper-ocean vertical mixing in the Antarctic Polar Front Zone. Deep-Sea Res. 52, 1087–1108 (2005).

    Google Scholar 

  23. Wu, L., Jing, Z., Riser, S. & Visbeck, M. Seasonal and spatial variations of Southern Ocean diapycnal mixing from Argo profiling floats. Nature Geosci. 4, 363–366 (2011).

    Article  Google Scholar 

  24. Frants, M. et al. Analysis of horizontal and vertical processes contributing to natural iron supply in the mixed layer in southern Drake Passage. Deep-Sea Res. II 90, 68–76 (2013).

    Article  Google Scholar 

  25. Ellwood, M. J., Boyd, P. W. & Sutton, P. Winter-time dissolved iron and nutrient distributions in the Subantarctic Zone from 40–52S; 155–160E. Geophys. Res. Lett. 35, L11604 (2008).

    Article  Google Scholar 

  26. Wagener, T., Guieu, C., Losno, R., Bonnet, S. & Mahowald, N. Revisiting atmospheric dust export to the Southern Hemisphere ocean: Biogeochemical implications. Glob. Biogeochem. Cycles 22, GB2006 (2008).

    Article  Google Scholar 

  27. Lannuzel, D. et al. Distribution of dissolved iron in Antarctic sea ice: Spatial, seasonal, and inter-annual variability. J. Geophys. Res. 115, G03022 (2010).

    Article  Google Scholar 

  28. Lin, H., Rauschenberg, S., Hexel, C. R., Shaw, T. J. & Twining, B. S. Free-drifting icebergs as sources of iron to the Weddell Sea. Deep-Sea Res. II 58, 1392–1406 (2011).

    Article  Google Scholar 

  29. Raiswell, R., Benning, L. G., Tranter, M. & Tulaczyk, S. Bioavailable iron in the Southern Ocean: the significance of the iceberg conveyor belt. Geochem. Trans. 9, 7 (2008).

    Article  Google Scholar 

  30. Gerringa, L. J. A. et al. Iron from melting glaciers fuels the phytoplankton blooms in Amundsen Sea (Southern Ocean): Iron biogeochemistry. Deep-Sea Res. II 71–76, 16–31 (2012).

    Article  Google Scholar 

  31. Nishioka, J., Ono, T., Saito, H., Sakaoka, K. & Yoshimura, T. Oceanic iron supply mechanisms which support the spring diatom bloom in the Oyashio region, western subarctic Pacific. J. Geophys. Res. 116, C02021 (2011).

    Google Scholar 

  32. Sarthou, G. et al. The fate of biogenic iron during a phytoplankton bloom induced by natural fertilisation: Impact of copepod grazing. Deep-Sea Res. II 55, 734–751 (2008).

    Article  Google Scholar 

  33. Strzepek, R. F. et al. Spinning the ‘Ferrous Wheel’: The importance of the microbial community in an iron budget during the FeCycle experiment. Glob. Biogeochem. Cycles 19, GB4S26 (2005).

    Article  Google Scholar 

  34. Sunda, W. G. & Huntsman, S. A. Iron uptake and growth limitation in oceanic and coastal phytoplankton. Mar. Chem. 50, 189–206 (1995).

    Article  Google Scholar 

  35. Marchetti, A. et al. Ferritin is used for iron storage in bloom-forming marine pennate diatoms. Nature 457, 467–470 (2009).

    Article  Google Scholar 

  36. Arrigo, K. R., van Dijken, G. L. & Bushinsky, S. Primary production in the Southern Ocean, 1997–2006. J. Geophys. Res. 113, C08004 (2008).

    Article  Google Scholar 

  37. Mackie, D. S. et al. Biogeochemistry of iron in Australian dust: From eolian uplift to marine uptake. Geochem. Geophys. Geosys. 9, Q03Q08 (2008).

    Article  Google Scholar 

  38. Gaiero, D. M., Probst, J. L., Depetris, P. J., Bidart, S. M. & Leleyter, L. Iron and other transition metals in Patagonian riverborne and windborne materials: Geochemical control and transport to the southern South Atlantic Ocean. Geochim. Cosmochim. Acta 67, 3603–3623 (2003).

    Article  Google Scholar 

  39. Stammerjohn, S., Massom, R., Rind, D. & Martinson, D. Regions of rapid sea ice change: An inter-hemispheric seasonal comparison. Geophys. Res. Lett. 39, L06501 (2012).

    Article  Google Scholar 

  40. Dierssen, H. M. Perspectives on empirical approaches for ocean color remote sensing of chlorophyll in a changing climate. Proc. Natl Acad. Sci. USA 107, 17073–17078 (2010).

    Article  Google Scholar 

  41. Lovenduski, N. S. & Gruber, N. Impact of the Southern Annular Mode on Southern Ocean circulation and biology. Geophys. Res. Lett. 32, L11603 (2005).

    Article  Google Scholar 

  42. Séférian, R. et al. Skill assessment of three earth system models with common marine biogeochemistry. Clim. Dynam. 40, 2549–2573 (2012).

    Article  Google Scholar 

  43. Steinacher, M. et al. Projected 21st century decrease in marine productivity: a multi-model analysis. Biogeosciences 7, 979–1005 (2010).

    Article  Google Scholar 

  44. Misumi, K. et al. The iron budget in ocean surface waters in the 20th and 21st centuries: projections by the Community Earth System Model version 1. Biogeosci. Discuss. 10, 8505–8559 (2013).

    Article  Google Scholar 

  45. Marinov, I., Doney, S. C. & Lima, I. D. Response of ocean phytoplankton community structure to climate change over the 21st century: Partitioning the effects of nutrients, temperature and light. Biogeosciences 7, 3941–3959 (2010).

    Article  Google Scholar 

  46. Henson, S., Cole, H., Beaulieu, C. & Yool, A. The impact of global warming on seasonality of ocean primary production. Biogeosciences 10, 4357–4369 (2013).

    Article  Google Scholar 

  47. Sallee, J. B., Wienders, N., Speer, K. & Morrow, R. Formation of subantarctic mode water in the southeastern Indian Ocean. Ocean Dynam. 56, 525–542 (2006).

    Article  Google Scholar 

  48. De Boyer Montegut, C., Madec, G., Fischer, A. S., Lazar, A. & Iudicone, D. Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology. J. Geophys. Res. 109, C12003 (2004).

    Article  Google Scholar 

  49. Strzepek, R. F., Maldonado, M. T., Hunter, K. A., Frew, R. D. & Boyd, P. W. Adaptive strategies by Southern Ocean phytoplankton to lessen iron limitation: Uptake of organically complexed iron and reduced cellular iron requirements. Limnol. Oceanogr. 56, 1983–2002 (2011).

    Article  Google Scholar 

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Acknowledgements

We thank all observational scientists that generously shared iron data (especially M. Klunder and P. Sedwick, who did so before publication), the GEOTRACES programme (www.geotraces.org), K. Arrigo and G. van Dijken for providing iron utilization data files and A. Barton for comments on the manuscript. The Argo float data were collected and made freely available by the International Argo Program (http://www.argo.ucsd.edu). This work benefitted from the support of the French Agence Nationale de la Recherche (ANR) grant ANR-10-LABX-18-01 of the national Programme Investissements d’Avenir, the CSIR Parliamentary Grant, NRF-SANAP and the EU FP7 Marie Curie International Research Staff Exchange Scheme (IRSES) Fellowship SOCCLI (The role of Southern Ocean Carbon cycle under CLImate change), which received funding from the European Commission’s Seventh Framework Programme under grant agreement 317699. J.B.S. received support from Agence Nationale de la Recherche (ANR), ANR-12-PDOC-0001, as well as from the British Antarctic Survey as a BAS Fellow. This research was partly supported by the Australian Government Cooperative Research Centres Programme through the Antarctic Climate and Ecosystems CRC (ACE CRC), University of Tasmania Rising Stars grant no B0019024 and Australian Antarctic Science project no 2900, the New Zealand Ministry for Science and Innovation and the Institute of Marine and Antarctic Studies, University of Tasmania.

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Led design of the study and writing of the manuscript (A.T.), assembly of the iron and Argo datasets and data analysis (A.T. and J-B.S.), additional physical flux analyses (A.T., J-B.S., M.L. and S.S.), biological rate measurements (P.W.B.) and additional iron observations (A.R.B.). All authors contributed to the overall experimental work, discussion of the results and their implications, as well as commenting on the manuscript.

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Correspondence to Alessandro Tagliabue.

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Tagliabue, A., Sallée, JB., Bowie, A. et al. Surface-water iron supplies in the Southern Ocean sustained by deep winter mixing. Nature Geosci 7, 314–320 (2014). https://doi.org/10.1038/ngeo2101

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