[M-IS26] 生物地球化学

[MIS26-10] 海洋溶存有機窒素の起源：アミノ酸窒素同位体組成分析からの制約

*山口 保彦¹、Taylor A. B. Broek¹、Matthew D. McCarthy¹ (1.カリフォルニア大学サンタクルーズ校)

キーワード：溶存有機物, 窒素循環, アミノ酸, 同位体, 北太平洋亜熱帯環流, メキシコ湾

Estimating sources of marine dissolved organic matter (DOM) is one of crucial steps for mechanistic understanding of marine biogeochemical cycles. Bacteria have been suggested as important sources of marine DOM, but nature of the source Bacteria (e.g., heterotrophic v.s. autotrophic) currently remains uncertain. While compound-specific isotope analysis of amino acids (CSI-AA) can be a powerful tool for elucidation of the source of marine DOM, it has been difficult due to the large analytical errors of CSI-AA associated with the complexity of marine DOM. Here we developed a new method for precise d15N-AA analysis of marine DOM by coupling HPLC purification and GC-IRMS, and then applied the method to high-molecular-weight (HMW) DOM samples collected at the Gulf of Mexico and the North Pacific Subtropical Gyre. d15N-AA values and patterns of the HMW-DOMs were significantly different between the surface and the mesopelagic depths, indicating that their sources are different. Especially, the d15N-AA signatures of the mesopelagic HMW-DOMs suggest that they are product of resynthesis by heterotrophic Bacteria, rather than remnant of DOM produced by autotrophic Bacteria.