Hydrothermal venting along mid-ocean ridges exerts an important control on the chemical composition of sea water by serving as a major source or sink for a number of trace elements in the ocean1, 2, 3. Of these, iron has received considerable attention because of its role as an essential and often limiting nutrient for primary production in regions of the ocean that are of critical importance for the global carbon cycle4. It has been thought that most of the dissolved iron discharged by hydrothermal vents is lost from solution close to ridge-axis sources2, 5 and is thus of limited importance for ocean biogeochemistry6. This long-standing view is challenged by recent studies which suggest that stabilization of hydrothermal dissolved iron may facilitate its long-range oceanic transport7, 8, 9, 10. Such transport has been subsequently inferred from spatially limited oceanographic observations11, 12, 13. Here we report data from the US GEOTRACES Eastern Pacific Zonal Transect (EPZT) that demonstrate lateral transport of hydrothermal dissolved iron, manganese, and aluminium from the southern East Pacific Rise (SEPR) several thousand kilometres westward across the South Pacific Ocean. Dissolved iron exhibits nearly conservative (that is, no loss from solution during transport and mixing) behaviour in this hydrothermal plume, implying a greater longevity in the deep ocean than previously assumed6, 14. Based on our observations, we estimate a global hydrothermal dissolved iron input of three to four gigamoles per year to the ocean interior, which is more than fourfold higher than previous estimates7, 11, 14. Complementary simulations with a global-scale ocean biogeochemical model suggest that the observed transport of hydrothermal dissolved iron requires some means of physicochemical stabilization and indicate that hydrothermally derived iron sustains a large fraction of Southern Ocean export production.
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Extended data figures and tables
Extended Data Figures
- Extended Data Figure 1: Relationship between dissolved trace metals and 3HE. (159 KB)
Depth-integrated concentrations of dissolved Fe (a), and dissolved Mn (b), versus depth-integrated concentration of 3Hexs, over a depth range of 2,200–2,640 m. Sample station numbers are indicated for each data symbol.
- Extended Data Figure 3: Sections of modelled Fed transport and decay using a dynamic ligand global-circulation model45 (see Methods). (631 KB)
The model scenarios listed here are the same as those presented in Fig. 4. a, 1 × Fe; b, 10 × Fe; c, 1 × Fe + 1 × ligands; d, 1 × Fe + 10 × ligands; e, 10 × Fe + 10 × ligands.
- Extended Data Figure 4: Impacts on carbon export from model simulations. (467 KB)
a, Percentage contribution to carbon export production due to the input of hydrothermal Fed, not considering the addition of hydrothermal ligands. b, Additional percentage contribution from the addition of hydrothermal ligands to the simulation shown in a. b represents the difference between the total impact from the addition of both hydrothermal Fed and ligands (see Fig. 4c) compared to the input hydrothermal Fed without the addition of the ligands shown in a.
- Extended Data Figure 5: Ligand flux model experiments. (206 KB)
Two experiments were run to assess the impact of the flux of ligands associated with hydrothermal activity on the oceanic budget. a, Model simulation with no hydrothermal ligand flux. b, Model simulation with ligand flux equal to the flux of hydrothermal Fe.