Fate of Refractory Dissolved Organic Matter: Aggregation with bubbling

2022 Fiscal Year Final Research Report

• Project/Area Number: 17K20040
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Research Field: Environmental analyses and evaluation and related fields
• Research Institution: University of Tsukuba
• Principal Investigator: Wada Shigeki 筑波大学, 生命環境系, 助教 (60512720)
• Co-Investigator(Kenkyū-buntansha): 佐藤 雄飛 公益財団法人環境科学技術研究所, 環境影響研究部, 研究員 (50708120)
• Project Period (FY): 2017-06-30 – 2023-03-31
• Keywords: 泡 / 溶存態有機物 / 凝集 / 難分解性 / 放射性炭素年代 / 脂肪酸組成

Outline of Final Research Achievements

In this study, we aimed to verify the aggregation of dissolved organic matter (DOM) in seawater by bubbling as one of its fates. Specifically, we evaluated whether refractory DOM, which takes thousands of years to decompose, undergoes aggregation based on the composition of organic matter and radiocarbon age.

By filtering seawater from multiple marine areas and aerating the filtrate with pure air, we successfully confirmed the aggregation of DOM. Furthermore, we collected the aggregates with foam in the field and measured their radiocarbon isotopes, which indicated that the organic matter was mostly modern. This finding is not contradictory, as the fatty acid composition of the aggregated organic matter aligns closely with the suspended particulate organic matter (POM) fraction, which contains a significant amount of present-day organic matter such as phytoplanktonic organic matter.

Free Research Field

生物地球化学

Academic Significance and Societal Importance of the Research Achievements

予想された結果(難分解性DOMの粒子化)とは異なる結果が得られたものの、易分解性有機物が泡によって選択的に粒子化されることが明らかとなり、植物プランクトンを由来とする有機物が短時間の間に粒子化するプロセスの存在が示された。有機物の凝集は、海中における粒子の生成過程として重要である一方、凝集過程は多くが未解明である。特に研究例がほとんど無い、泡が介在する有機物粒子の動態が明らかになったことは、荒天時など特に泡が生じやすい条件が炭素循環に及ぼす影響を解明する上で重要な情報となりうる。