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

• Published in: Nature Genetics
• Main Authors: Tagliabue, A, Sallee, JB, Bowie, AR, Levy, M, Swart, S, Boyd, PW
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Publishing Group 2014
• Subjects: Earth Sciences; Oceanography; Chemical oceanography; Antarctic; Southern Ocean; Antarc*
• Online Access: https://doi.org/10.1038/ng.2554; https://doi.org/10.1038/NGEO2101; http://ecite.utas.edu.au/90755

Low levels of iron limit primary productivity across much of the Southern Ocean. At the basin scale, most dissolved iron issupplied to surface waters from subsurface reservoirs, because land inputs are spatially limited. Deep mixing in winter togetherwith year-round diffusion across density surfaces, known as diapycnal diffusion, are the main physical processes that carryiron-laden subsurface waters to the surface. Here, we analyse data on dissolved iron concentrations in the top 1,000 m of theSouthern Ocean, taken from all known and available cruises to date, together with hydrographic data to determine the relativeimportance of deep winter mixing and diapycnal diffusion to dissolved iron fluxes at the basin scale. Using information onthe vertical distribution of iron we show that deep winter mixing supplies ten times more iron to the surface ocean eachyear, on average, than diapycnal diffusion. Biological observations from the sub-Antarctic sector suggest that following thedepletion 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 SouthernOcean primary production.