Hydrothermal plumes in the Gulf of Aden, as characterized by light transmission, Mn, Fe, CH₄ and δ¹³C-CH₄ anomalies

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• 作者：Toshitaka Gamo^a ; ¹ ; ^{gamo@aori.u-tokyo.ac.jp" class="auth_mail" title="E-mail the corresponding author} ; Kei Okamura^b ; ² ; Hiroshi Hatanaka^c ; Hiroshi Hasumoto^d ; Daisuke Komatsu^a ; ³ ; Masakazu Chinen^e ; Mutsumi Mori^e ; Junya Tanaka^f ; Akinari Hirota^a ; ⁴ ; Urumu Tsunogai^a ; ⁵ ; Kensaku Tamaki^d
• 关键词：Hydrothermal plumes ; Gulf of Aden ; Submarine hydrothermal activity ; Water column surveys ; Geochemical tracers ; Volcanic seamounts ; Light transmission anomaly ; Helium isotopes ; Carbon isotopes of methane ; Iron ; Manganese ; Magmatic methane
• 刊名：Deep Sea Research Part II: Topical Studies in Oceanography
• 出版年：2015
• 出版时间：November 2015
• 年：2015
• 卷：121
• 期：Complete
• 页码：62-70
• 全文大小：4274 K

文摘

We conducted water column surveys to search for hydrothermal plumes over the spreading axes in the Gulf of Aden between 45°35′E and 52°42′E. We measured light transmission and chemical tracers Mn, Fe, CH₄ and δ¹³C of CH₄ in seawater taken using a CTD-Carrousel multi-sampling system at 12 locations including a control station in the Arabian Sea. We recognized three types of hydrothermal plumes at depths of ~650 to ~900 m (shallow plumes), ~1000 to ~1200 m (intermediate plumes), and >1500 m (deep plumes). The shallow plumes were apparently originated from newly discovered twin seamounts (12°03–06′N and 45°35–41′E) at the westernmost survey area, where two-dimensional distributions of light transmission and Mn were mapped by tow-yo observations of the CTD-sampling system with an in situ auto-analyzer GAMOS. The maximum concentrations of Mn, Fe, and CH₄ of 46 nM, 251 nM, and 15 nM, respectively, were observed for collected seawater within the shallow plumes. The intermediate plumes were characterized by anomalies of light transmission, Mn, Fe, and δ¹³C of CH₄, but by little CH₄ anomalies, suggesting that CH₄ had been consumed down to the background level during the aging of the plumes. Anomalies of δ³He already reported by the World Ocean Circulation Experiment (WOCE) program exhibited a hydrothermal plume-like peak at ~2000 m depth in the Gulf of Aden, which seems to coincide with the deep plumes observed in this study. The endmember δ¹³C–CH₄ values for the shallow and the deep plumes were estimated to be in a range between −10‰ and −15‰, demonstrating that the sources of CH₄ are not biogenic but magmatic as similarly observed at sediment-starved mid-oceanic ridges.