Surface Ocean Biogeochemistry Regulates the Impact of Anthropogenic Aerosol Fe Deposition on the Cycling of Iron and Iron Isotopes in the North Pacific. Issue 13 (2nd July 2022)

• Record Type: Journal Article
• Authors: König, D.; Conway, T. M.; Hamilton, D. S.; Tagliabue, A.
• Is Part Of: Geophysical research letters. Volume 49:Issue 13(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-07-02
• Subjects: anthropogenic iron -- iron isotopes -- model -- ocean -- biogeochemistry; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL098016
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Distinctively‐light isotopic signatures associated with Fe released from anthropogenic activity have been used to trace basin‐scale impacts. However, this approach is complicated by the way Fe cycle processes modulate oceanic dissolved Fe (dFe) signatures (δ 56 Fediss ) post deposition. Here we include dust, wildfire, and anthropogenic aerosol Fe deposition in a global ocean biogeochemical model with active Fe isotope cycling, to quantify how anthropogenic Fe impacts surface ocean dFe and δ 56 Fediss . Using the North Pacific as a natural laboratory, the response of dFe, δ 56 Fediss, and primary productivity are spatially and seasonally variable and do not simply follow the footprint of atmospheric deposition. Instead, the effect of anthropogenic Fe is regulated by the biogeochemical regime, specifically the degree of Fe limitation and rates of primary production. Overall, we find that while δ 56 Fediss does trace anthropogenic input, the response is muted by fractionation during phytoplankton uptake, but amplified by other isotopically‐light Fe sources. Plain Language Summary: Iron released into the atmosphere by anthropogenic activities (e.g., combustion, metal industry) can get transported to open ocean areas, where it can fertilize biological production upon deposition. The distinctively‐light isotopic signatures of such anthropogenic iron have been used to trace its oceanic impact, and disentangle its contribution from that of other external iron sources. However, this approach is complicated by fractionation during surface ocean processing, which can affect the dissolved iron isotopic signature. To quantify the impact of anthropogenic iron on surface ocean iron and its isotopes, we added iron deposition from anthropogenic and other (dust, wildfire) sources to a global ocean model which incorporates iron isotopes. Focusing on the North Pacific, we find the impact of anthropogenic iron varies in time and space, whereby changes in iron concentration and isotopic signatures are distinct and also differ from the footprint of atmospheric deposition. These discrepancies relate to differences in biology, specifically the productivity of a surface ocean system, and whether this productivity is limited by the availability of iron. We find dissolved iron isotopic signatures to be useful to trace anthropogenic iron, provided that fractionating (biological) processes and the impact of other external iron sources are accounted for. Key Points: Anthropogenic Fe deposition has a variable impact on surface ocean biogeochemistry which can differ from the pattern of deposition Anthropogenic Fe drives distinct responses in primary production, dFe and δ 56 Fediss, dependent on the surface ocean biogeochemical regime δ 56 Fediss traces anthropogenic Fe impact, but requires careful evaluation of other Fe sources and isotope fractionation during Fe uptake