The Southern Ocean is the site of 20% of global ocean carbon export, and the origin of water masses that significantly impact the chemistry of the global ocean. Much of the Southern Ocean is a high nutrient low chlorophyll (HNLC) region. Iron is the primary limiting nutrient for phytoplankton growth, and may also be an important control on the biogeochemistry of the water masses emanating from the Southern Ocean. Here we investigate the response of Zn and Ni and their isotopes to natural Fe fertilization from Southern Ocean islands, using samples collected during the KEOPS-2 (Oct-Nov 2011) program in the early austral spring near the Kerguelen plateau, Indian Sector of the Southern Ocean.Zinc and Ni concentrations show depth distributions and relationships to major nutrients that are very similar to published data from the Atlantic sector of the Southern Ocean, away from island fertilization. As in the Atlantic sector, and other regions outside the Southern Ocean, there is a slight minimum in d 66 Zn at about 100-150m depth and a slightly heavier value at the surface. At the KEOPS-2 sites, the light sub-surface Zn isotopes occur at the depth level where measured chl-a has declined to near zero. The heaviest Zn isotope values in either the Atlantic or Indian sectors occur in bottom waters, are associated with samples that show high dissolved Si relative to Zn. These latter represent possible evidence for a heavy input directly to deep water or from sediment, and the Zn-Si-d 66 Zn systematics are consistent with a source in diatom opal. Nickel concentrations show much less variation than those of Zn, with the most depleted surface value only 15-20% lower than those in upwelled deep water in the Southern Ocean. These small variations in Ni concentration are associated with no significant variability in Ni isotopes, as also previously observed in the Atlantic sector.Overall, the key feature of the dataset is the apparent absence of any significant impact of natural Fe fertilization on the distribution of Zn and Ni, with the dominant control being the station location relative to the Polar Front in both the Atlantic and Indian sectors. Zinc and Ni isotopes are invariant in surface waters, whether inside or outside the fertilised zone and whether south or north of the Polar Front.

In this study, we report seawater dissolved zinc (Zn) concentration and isotope composition (δ 66 Zn) from the GEOTRACES GA01 (GEOVIDE) section in the North Atlantic. Across the transect, three subsets of samples stand out due to their isotopically light signature: those close to the Reykjanes Ridge, those close to the sediments, and those, pervasively, in the upper ocean. Similar to observations at other locations, the hydrothermal vent of the Reykjanes Ridge is responsible for the isotopically light Zn composition of the surrounding waters, with an estimated source δ 66 Zn of-0.42‰. This isotopically light Zn is then transported over a distance greater than 1000km from the vent. Sedimentary inputs are also evident all across the transAtlantic section, highlighting a much more pervasive process than previously thought. These inputs of isotopically light Zn, ranging from-0.51 to +0.01 ‰, may be caused by diffusion out of Zn-rich pore waters, or by dissolution of sedimentary particles. The upper North Atlantic is dominated by low δ 66 Zn, a feature that has been observed in all Zn isotope datasets north of the Southern Ocean. Using macronutrient to Zn ratios to better understand modifications of preformed signatures exported from the Southern Ocean, we suggest that low upper-ocean δ 66 Zn results from addition of isotopically light Zn to the upper ocean, and not necessarily from removal of heavy Zn through scavenging. Though the precise source of this isotopically light upper-ocean Zn is not fully resolved, it seems possible that it is anthropogenic in origin. This view of the controls on upper-ocean Zn is fundamentally different from those put forward previously.