Development of environmental chemistry on the evaporation of metal elements by isotope fractionation

2019 Fiscal Year Final Research Report

• Project/Area Number: 16K13911
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Geochemistry/Cosmochemistry
• Research Institution: The University of Tokyo
• Principal Investigator: Takahashi Yoshio 東京大学, 大学院理学系研究科(理学部), 教授 (10304396)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: 金属元素 / 気化 / 同位体分別 / 環境地球化学 / エアロゾル / 化学種 / 人為起源

Outline of Final Research Achievements

Dissolved iron (Fe) concentration is one of limiting factors of primary production in the opne ocean. It has been reported that anthropogenic Fe in aerosol is more soluble to water compared with crustal Fe. However, the contribution of anthropogenic Fe to the surface ocean remains unclear. In the present study, we focused on anthropogenic Fe in aerosols and aimed to clarify the Fe isotope ratio of anthropogenic Fe in aerosols, associated with its solubility, formation process, and contribution to the surface ocean. Our results suggested that (i) anthropogenic aerosols in fine particles contained oxidized Fe species and (ii) δ56Fe of fine particles (<1 μm) were －2.01‰, much lower than crustal rocks. From these results, it was suggested that anthropogenic Fe yields very low δ56Fe because of large isotope fractionation during evaporation process. This suggests that δ56Fe can be a useful tracer for anthropogenic Fe and is an important key to model the Fe cycle in the surface ocean.

Free Research Field

地球化学、環境化学

Academic Significance and Societal Importance of the Research Achievements

本研究では、気候変動にも影響を与える海洋の生物一次生産の支配因子であるエアロゾル中の溶解性鉄の濃度に、人為的な燃焼由来の鉄が影響を与えることを、微量な鉄安定同位体比の分析から明らかにした。特に発生源近傍での分析などからこの同位体分別を明確にしたことと、実際の北太平洋での観測から粒径が小さな成分で鉄安定同位体比が低かったことから、海洋エアロゾル中の人為起源の鉄の寄与を明確にした点が特筆される。また鉄安定同位体比と鉄の水溶解性には正の相関があり、人為燃焼起源鉄ほど海洋への溶解率が高いことが示唆された。そのため、絶対濃度は低くても、人為燃焼起源鉄の海洋一次生産への寄与は無視できないことが示唆された。