[A-CG42] 北極域の科学

[ACG42-P16] Was the increasing temperature of warm mid-depth Atlantic water triggering methane hydrate instability in the Alaskan Beaufort margin during the late Holocene?

*内田 昌男¹、万徳 佳菜子¹、久保田 好美²、山田 桂³、山口 滉介³、熊田 英峰⁴、Stephan Rella¹、西野 茂人⁵、伊東 素代⁵ (1.国立研究開発法人国立環境研究所、2.独立行政法人国立科学博物館、3.信州大学、4.東京薬科大学、5.国立研究開発法人海洋研究開発機構)

キーワード：ボーフォート海、メタンハイドレート、北極海、大西洋起源中層水、完新世

Alaskan Beaufort margin bears large abundances of methane hydrate (Ruppel et al.,2011). From marine marginal sediments all over the world during the late Pleistocene, previously reported direct and indirect evidence accumulated from geochemical data from marginal sea sediment suggests that methane episodically released from hydrate trapped in the seafloor sediments (Kennett et al., 2000; Uchida et al., 2006, 2008; Cook et al., 2011). Here, we investigated the relationships between marginal sea environmental changes, including hydrate instability and increasing temperature of warm intermediate water derived from the Atlantic Ocean in the Alaskan Beaufort margin. We analyzed high-resolution ¹⁴C ages of calcareous fossil and organic matter, stable isotopes of foraminifera, molecular markers, and Mg/Ca ratios of Ostracoda from piston cores collected in Alaskan Beaufort Margin. Our data showed highly depleted ¹³C compositions of benthic foraminifera, suggesting indirect records of enhanced incorporation of ¹³C depleted CO₂ formed by methanotrophic processes that use ¹²C-enriched methane as their primary carbon source. Their signals showed highly synchronized variability with intermediate water temperature. This is the first evidence of past methane hydrate dissociation in the Alaskan margin. Our data suggests that the methane cycle in Arctic marginal regions may be modulated by Atlantic warm intermediate water warming and/or the lowering of sea level, influencing a profound effect on future warming climate changes.