Major lithogenic contributions to the distribution and budget of iron in the North Pacific Ocean

Linjie Zheng,Yoshiki Sohrin

doi:10.1038/s41598-019-48035-1

Abstract

Recent studies have elucidated that iron (Fe) is a critical trace metal that influences the productivity of marine ecosystems and the biogeochemical cycles of other elements in the modern ocean. However, our understanding of the biogeochemistry of Fe remains incomplete. Herein, we report 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, as observed during three cruises of the GEOTRACES Japan program. We found that lpFe dominates tdFe and is significantly correlated with labile particulate aluminum (lpAl): lpFe [nmol kg−1] = (0.544 ± 0.005) lpAl [nmol kg−1] + 0.11 ± 0.04, r2 = 0.968, n = 432. The results indicate a major lithogenic contribution to the distribution of particulate Fe. For dFe, the unique distribution is attributed to the combined effects of biogeochemical cycling, manganese reduction, and lithogenic contribution. Based on concurrent observations of Fe, Al, and manganese (Mn), we infer that the width of the boundary scavenging zone is approximately 500 km off the Aleutian shelf. We estimate the inventory of tdFe in the North Pacific as 1.1 × 1012 mol, which is approximately four times that of dFe. Our results emphasize the potential importance of lpFe in the ocean’s iron cycle.

Highlights

Iron (Fe) is an abundant element in the upper crust, with an average concentration of 39 mg g–1 and a mole ratio of Fe/Al = 0.231, it exhibits a low concentration in the order of nmol kg−1 in the modern ocean
Most global marine biogeochemical iron cycling models do not focus on pFe25,26; particulate Fe (pFe) can be directly utilized by organisms[27,28,29,30,31], and dFe–pFe interactions occur in seawater[32,33]
The present study was conducted on samples and data acquired during the following cruises of R/V Hakuho Maru: KH-05-2 from August to September 2005, KH-11-7 in July 2011, and KH-12-4 from August to September 2012 (Supplementary Fig. 1)

Summary

Introduction

The observed range of lpFe/lpAl ratios in this study appears representative of oceans generally since it encompasses the reported Fe/Al ratios in suspended particles, including 0.30–0.41 from the North Pacific Gyre[18] and 0.27–0.33 from the Sargasso Sea[49]. The concentrations of dFe and phosphate below a depth of 4500 m are plotted against latitude in Supplementary Fig. 8c,d, respectively.

Results

Conclusion