Trace metals shape both the biogeochemical functioning and biological structure of oceanic provinces. Trace metal biogeochemistry has primarily focused on modes of external supply of metals from aeolian, hydrothermal, sedimentary and other sources. However, metals also undergo internal transformations such as abiotic and biotic retention, recycling and remineralization. The role of these internal transformations in metal biogeochemical cycling is now coming into focus. First, the retention of metals by biota in the surface ocean for days, weeks or months depends on taxon-specific metal requirements of phytoplankton, and on their ultimate fate: that is, viral lysis, senescence, grazing and/or export to depth. Rapid recycling of metals in the surface ocean can extend seasonal productivity by maintaining higher levels of metal bioavailability compared to the influence of external metal input alone. As metal-containing organic particles are exported from the surface ocean, different metals exhibit distinct patterns of remineralization with depth. These patterns are mediated by a wide range of physicochemical and microbial processes such as the ability of particles to sorb metals, and are influenced by the mineral and organic characteristics of sinking particles. We conclude that internal metal transformations play an essential role in controlling metal bioavailability, phytoplankton distributions and the subsurface resupply of metals.
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The authors thank G. Jackson (Texas A&M University) and T. Kiørboe (Technical University of Denmark) for the provision of unpublished data/video footage. The authors acknowledge the role of collaborations with David Hutchins, Sylvia Sander, Robert Strzepek and Steve Wilhelm in developing this Perspective. The sinking particles presented in Supplementary Fig. 2c were collected by Z. Baumann (University of Connecticut) and analysed with the assistance of D. Ohnemus (Bigelow Laboratory for Ocean Sciences). This analysis used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Support was provided by Australian Research Council Australian Laureate Fellowship project FL160100131 and Antarctic Climate and Ecosystems Cooperative Research Centre funding to P.W.B., an Australian Research Council Discovery Project DP130100679 to M.J.E. and P.W.B. B.S.T. was supported by US National Science Foundation grant OCE-1232814. Model simulations by A.T. are supported by N8 HPC Centre of Excellence, provided and funded by the N8 consortium and EPSRC (Grant No. EP/K000225/1).
The authors declare no competing financial interests.
Supplementary Figures and Tables (PDF 853 kb)
Animation of heterotrophic microflagellatesattached to a particle and feeding on free-living and particle-attached bacteria. The particle was created from a latex bead coated in an organic substrate to promote microbial colonisation. The video reveals that the surface of such biogenic particles in the ocean is likely a 'hotspot' of iron recycling and release, the balance of which is dependent on the small scale trace metal chemistry as outlined in Figure 3 and S-Figure 2 (Courtesy of Thomas Kiørboe, Technical University of Denmark). (WMV 4026 kb)
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Boyd, P., Ellwood, M., Tagliabue, A. et al. Biotic and abiotic retention, recycling and remineralization of metals in the ocean. Nature Geosci 10, 167–173 (2017). https://doi.org/10.1038/ngeo2876
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