[M-IS15] 古気候・古海洋変動

[MIS15-P14] ベーリング海バウアーズ海嶺コア堆積物に記録された退氷期の海洋環境と炭酸カルシウムピーク

*岡崎 裕典¹、緒方 健人¹、山本 愛佳¹、関 宰² (1.九州大学大学院理学研究院地球惑星科学部門、2.北海道大学低温科学研究所)

Two neighboring sediment cores obtained from the western flank of the Bowers Ridge BOW-9A (54°2.23’N, 178°40.58’E, 2391 m) and U1341C (54°2.00’N, 179°0.54’E, 2139.5 m) were used in this study to discuss the paleoceanographic changes in the southern Bering Sea during the last deglaciation. Both sedimentary records showed pronounced millennial-scale changes responding to the “Greenland-like” climate changes characterized by the Bølling–Allerød (BA) and Preboreal (PB) warmings and the Younger Dryas (YD) cooling. Biogenic opal, CaCO3, and organic carbon contents and Br intensity by ITRAX XRF core scanner increased during the BA period, suggesting high productivity. The high productivity is supported by abundant Neodenticula seminae, a representative diatom species in the subarctic Pacific. A sharp abundance peak of Thalassiosira hyalina during BA suggests meltwater input into the Bering Sea. Rhizoplegma boreale, a radiolarian species abundant in the polar coastal regions, and Cycladophora davisiana, a radiolarian species dwelling in well-ventilated intermediate water, were also abundant during the BA period. These diatom and radiolarian species support the presence of meltwater and well-ventilated intermediate water in the southern Bering Sea. On the contrary, during the YD period, productivity proxies decreased. Instead, concentrations of odd number C25–C31 n-alkanes, organic compounds primarily originate from terrestrial vascular plants, increased, atmospherically transported from the Beringia and the Aleutian Islands. We found an extremely high Ca intensity peak at ~120 cm in Core U1341C, corresponding to the YD period. The peak was not found in Core BOW-9A, where two CaCO3 peaks during BA and PB periods. The Radiocarbon date of the planktic foraminifera (Neogloboquadrina pachyderma sinistral) showed 14.3 cal. kyr BP, age in the middle of BA. Furthermore, three planktic foraminiferal 14C dates below 190 cm core depth in U1341C were unexpectedly young, showing BA ages. Such 14C dates were not found in BOW-9A. We suspect the planktic foraminiferal shells living deposited during BA periods were selectively reworked and distributed to the deeper depths by bioturbation.