Paleocirculation of the Western Boundary Undercurrent (WBUC) at the Eirik Drift

• Main Authors: Mueller-Michaelis, Antje, Uenzelmann-Neben, Gabriele
• Format: Conference Object
• Language: unknown
• Published: 2013
• Subjects: Greenland; Denmark Strait; Iceland; North Atlantic
• Online Access: https://epic.awi.de/id/eprint/32219/; https://hdl.handle.net/10013/epic.40853

Growing interest in climate research and the coupled ocean-atmosphere interactions has led to numerous studies of the modern and ancient global ocean Thermohaline Circulation (THC). In the North Atlantic the Western Boundary Undercurrent (WBUC) forms the deep branch of the THC. The Eirik Drift, which lies on the slope south of Greenland, has been formed under the influence of this WBUC. The sediment record at the Eirik Drift thus documents changes in pathways and intensity of the WBUC and bears information about modifications of the North Atlantic THC in a changing climate. A study of the sedimentation history of the Eirik Drift will hence allow a deciphering of climate development and modifications in the Neogene. High resolution seismic reflection data collected during RV Maria S. Merian cruise MSM 12/2 were incorporated with geological information from ODP Leg 105 and IODP Expedition 303 Sites and led to a seismostratigraphic analysis of sedimentary structures. For the first time a detailed reconstruction of the palaeocirculation of the WBUC at the Eirik Drift since the Micoene is conducted. We date the onset of drift building under the influence of an intense WBUC at ~19 Ma. The WBUC remains strong from 19 to 10 Ma. Then it weakens and shallows gradually until 5.6 Ma. A separation of the WBUC into two branches at different core depths along with a renewed intensification is observed at 5.6 Ma. These two branches presumably transport Denmark Strait Overflow Water (lower branch) and Iceland Scotland Overflow Water (upper branch). The WBUC remains strong until ~2.5 Ma with a peak intensity at 4.5 Ma. We observe a gradual weakening and shallowing of the WBUC after 2.5 Ma. Thus, we observe a strong WBUC during warm phases (Miocene warm phase 20-15 Ma; Pliocene warm phase 5-3.6 Ma) as well as in the following cooling phases until pronounced ice-sheets are re-established (15-10 Ma; 3.6-2.75 Ma). The weakening of the WBUC takes place in the cooling phases after pronounced ice-sheets are re-established (10-5.6 Ma; < 2.5 Ma). Erosional unconformities are found at 19 Ma and 4.5 Ma close to the reversals of cooling to global warming phases (20 Ma and 5 Ma, respectively). The conjunction of warmer climate with an intensified NCW flow is ambiguous, as an intensified NCW circulation is a result of enhanced NCW production, which usually needs a colder environment.