Oceanic Margins as sources of lithogenic particulate and dissolved iron in the North Pacific Ocean

10 March 2020

Three GEOTRACES Japanese cruises on board the R/V Hakuho Maru allowed establishing basin-scale and full-depth sectional distributions of total dissolvable iron (tdFe), dissolved iron (dFe), and labile particulate iron (lpFe=tdFe – dFe) in the North Pacific Ocean. Zheng and Sohrin (2019, see reference below) also discuss aluminum (Al) and manganese (Mn) data in this work. Results emphasize a major contribution of lithogenic material to the Fe budget of this area. More specifically, they identify i) a clear correlation between labile particulate iron and labile particulate Al, with a ratio of 0.544 largely above the Fe/Al crustal ratio and ii) that the dFe is strongly enriched in the northern part of the North Pacific. Both relationships are shown on the Figure 1. Figure 2 emphasizes the impact of these margin inputs for the dFe concentrations at 1000 m for the whole North Pacific. The authors estimate a total inventory for tdFe and dFe in this area equal to 1.1×10¹² mol and 2.8×10¹¹mol respectively. The difference of 8.2×10¹¹mol equates to the amount of lpFe. This first inventory of observed Fe fractions in the North Pacific reveals the potential importance of lpFe in the ocean iron cycle which may have been underestimated as a source of bioavailable so far.

**Figure 1:** Relationships between lpFe and lpAl, and between dFe and dAl in the North Pacific Ocean. These results suggest that particulate Fe is distributed in a similar manner with particulate Al, whereas dissolved Fe is decoupled with dissolved Al because of biological activity. Click on the figure to view it larger.

**Figure 2:** Horizontal distribution of dFe at a depth of 1000 m in the North Pacific Ocean. The black dots represent sampling stations. The figure shows that major sources of dissolved iron are northern continental margins and the Hawaii Islands. Click on the figure to view it larger.

Reference:

Zheng, L., & Sohrin, Y. (2019). Major lithogenic contributions to the distribution and budget of iron in the North Pacific Ocean. Scientific Reports, 9(1), 11652. https://doi.org/10.1038/s41598-019-48035-1

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