[A-CG42] Science in the Arctic Region

[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?

*Masao Uchida¹, Kanako Mantoku¹, Yoshimi Kubota², Katsura Yamada³, Kosuke Yamaguchi³, Hidetoshi Kumata⁴, Stephan Rella¹, Shigeto Nishino⁵, Motoyo Itoh⁵ (1.National Institute for Environmental Studies, 2.National Museum of Nature and Science, 3.Shinshu University, 4.Tokyo University of Pharmacy and Life Sciences, 5.Japan Agency for Marine-Earth Science and Technology)

Keywords:Beaufort Sea, methane hydrate, Arctic Ocean, mid-depth Atlantic water, Holocene

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.