Journal Article

The early Miocene onset of a ventilated circulation regime in the Arctic Ocean

Sangiorgi, Francesca, Moran, Kathryn, Backman, Jan, Mayer, Larry, King, John, Nycander, Jonas, Jokat, Wilfried, Brinkhuis, Henk, O’Regan, Matthew, Jakobsson, Martin, Rudels, Bert, Frank, Martin

2007

Overview

Birth of an ocean Deep-water formation in the northern North Atlantic and the Arctic Ocean is a key driver of global thermohaline circulation and hence of global climate. The lack of sediments from the Arctic's deep-sea floor has hampered research into this area, but this changed when drill cores were recovered from the central Arctic Ocean in 2004, during the ACEX experiment. This unique 428-metre-thick Cenozoic sediment sequence preserves a critical piece of palaeo-environmental history: the advent of the Arctic Ocean in its current form. The gradual opening of the Fram Strait resulted in a change from a land-enclosed lake-like water body to an estuarine 'Black Sea type' phase with variable ventilation, and finally to the fully ventilated 'ocean' phase, some 17.5 million years ago. Cores taken from the central Arctic Ocean in the 2004 ACEX experiment show that the Arctic Ocean went from an oxygen-poor 'lake stage', to a transitional 'estuarine sea' phase with variable ventilation, and finally to the fully ventilated 'ocean' phase, some 17.5 Myr ago. Deep-water formation in the northern North Atlantic Ocean and the Arctic Ocean is a key driver of the global thermohaline circulation and hence also of global climate 1 . Deciphering the history of the circulation regime in the Arctic Ocean has long been prevented by the lack of data from cores of Cenozoic sediments from the Arctic’s deep-sea floor. Similarly, the timing of the opening of a connection between the northern North Atlantic and the Arctic Ocean, permitting deep-water exchange, has been poorly constrained. This situation changed when the first drill cores were recovered from the central Arctic Ocean 2 . Here we use these cores to show that the transition from poorly oxygenated to fully oxygenated (‘ventilated’) conditions in the Arctic Ocean occurred during the later part of early Miocene times. We attribute this pronounced change in ventilation regime to the opening of the Fram Strait. A palaeo-geographic and palaeo-bathymetric reconstruction of the Arctic Ocean, together with a physical oceanographic analysis of the evolving strait and sill conditions in the Fram Strait, suggests that the Arctic Ocean went from an oxygen-poor ‘lake stage’, to a transitional ‘estuarine sea’ phase with variable ventilation, and finally to the fully ventilated ‘ocean’ phase 17.5 Myr ago. The timing of this palaeo-oceanographic change coincides with the onset of the middle Miocene climatic optimum 3 , although it remains unclear if there is a causal relationship between these two events.

• Publisher: Nature Publishing Group UK,Nature Publishing,Nature Publishing Group
• Subject: Arctic Ocean / Arctic Oscillation / Arctic Regions / Atlantic Ocean / Brackish / Cenozoic / Circulation / Cores / Deep sea / Deep water / Earth sciences / Earth, ocean, space / Ecosystem / Exact sciences and technology / Fresh Water - analysis / Geology / Global climate / History, Ancient / Humanities and Social Sciences / Lakes / letter / Marine / Marine geology / Miocene / multidisciplinary / Ocean circulation / Ocean floor / Oceanography / Oceans / Oxygen - analysis / Oxygenated / Phase transformations / Prehistoric era / Reconstruction / Science / Science (multidisciplinary) / Seawater - analysis / Seawater - chemistry / Straits / Stratigraphy / Thermohaline circulation / Time Factors / Time measurements / Ventilation / Water exchange / Water Movements