10.18170/DVN/KDLJEQ Xue, Pengfei Downward expansion of seawater deoxygenation during the Palaeocene-Eocene Thermal Maximum-亚洲成人在线一二三四五六区 Peking University Open Research Data Platform 2021 Downward expansion of seawater deoxygenation during the Palaeocene-Eocene Thermal Maximum Xue, Pengfei