Global warming caused widespread ocean anoxia 93 million years ago, deep-sea sediments research suggests

Marine anoxia is characterized by the oceans being severely depleted in dissolved oxygen, making them toxic and thus having devastating impacts on the organisms inhabiting them. One such event, known as Oceanic Anoxic Event 2 (OAE2), occurred ~93.5 million years ago across the Cenomanian-Turonian boundary of the Upper Cretaceous and lasted for up to 700,000 years.