North Atlantic Deep Water formed by the later middle Miocene

Abstract

There is evidence that in Mesozoic and Palaeogene times both north and south subpolar areas had a mild climate1,2. Unlike the present day climatic symmetry, with warm equatorial regions and ice-covered polar regions, a strong planetary asymmetry developed in the middle Miocene, when the Antarctic ice cap was established while the northern high latitudes remained unglaciated3. The symmetry was restored when a Northern Hemisphere continental ice cover was established ∼3 Myr ago in the middle Pliocene4. These changes influenced the formation of deep water in the ocean. At present the cold, dense bottom waters originate in only two high latitude areas—the Weddell Sea producing Antarctic Bottom Water, and the Norwegian Sea, producing Norwegian Sea Overflow Water which after mixing is a major component of the North Atlantic Deep Water. The production of cold deep water in the Southern Ocean started at the Eocene–Oligocene boundary3. We present here new evidence from isotope analyses of benthic Foraminifera from DSDP site 116 indicating that the production of oxygenated deep water in the North Atlantic Ocean started in the late middle-Miocene, ∼12 Myr ago.