[M-IS09] 生物地球化学

[MIS09-01] 太平深層に分布する深海熱水由来の熱成炭素

*山下 洋平^1,2、森 雄太郎²、小川 浩史³ (1.北海道大学 大学院地球環境科学研究院、2.北海道大学 大学院環境科学院、3.東京大学 大気海洋研究所)

キーワード：海洋、熱水、溶存有機物、熱成炭素、溶存黒色炭素

Pyrogenic carbon, a byproduct of biomass and fossil fuel combustion, is an important component in global carbon cycle because it can be stored on Earth’s surface for centuries to millennia. A part of pyrogenic carbon become dissolvable with oxidation. The dissolvable fraction of pyrogenic carbon is called dissolved black carbon (DBC). DBC is known to occur ubiquitously in the ocean. Although recent studies clarified that DBC in the deep ocean is removed via sorption onto sinking particles, the DBC cycle and budget in the ocean have not been well constrained. In particular, the missing source has been suggested by imbalance of the budget in the ocean. Deep hydrothermal vents are suggested to be a possible source of thermogenic DBC, but little is known about the distribution of hydrothermal DBC in the deep ocean. Here, we show the basin-scale distributions of DBC along two transects in the eastern Pacific Ocean. The concentration and condensation degree of deep ocean DBC at the sites close to the Eastern Pacific Rise were higher than those at the other sites, suggesting that highly condensed DBC was derived from hydrothermal systems and transported over long distances. The hydrothermal DBC concentration was quantified as a deviation from the linear relationship between the DBC concentration and apparent oxygen utilization previously observed in the central and western Pacific Ocean. The deviation was linearly correlated with excess 3He, a tracer of hydrothermal input, confirming the hydrothermal origin of the DBC. Our tentative estimate of global hydrothermal DBC fluxes, 1.6–9.7 TgC/year, corresponded to 8.9 to 53.9% of the riverine DBC flux to the ocean.