Oligocene climate dynamics towards the Oligocene-Miocene transition (IODP Expedition 342, North Atlantic)
Final Report Abstract
The principal objective of this project was to compile paleoclimate proxy records for the Oligocene to Miocene interval based on benthic and planktic foraminifera in order to understand the long-term climate evolution and how it relates to short-term variability. The project addressed the following three major research questions: (1) How does the deep ocean evolve along the Oligocene to early Miocene cooling trend? (2) Are the observed bottom-water dynamics triggered by orbital and/or suborbital mechanisms? and (3) How does the surface ocean respond to the Mi-1 event? To tackle these questions, well-preserved (glassy) planktic and benthic foraminifera from the extended drift records of IODP Sites U1405 and U1406, drilled during IODP Expedition 342 off Newfoundland were used. In order to answer Questions 1 and 2, a high-resolution (1.8 ky) benthic foraminiferal stable isotope record has been generated from Site U1406 in the framework of an international consortium comprising researchers from Germany, South Korea and the UK. This long-term record aims at understanding and documenting the dynamics and evolution of deep-water temperature and carbon cycle in a resolution which has never been carried out before in pre-Pliocene sediments, and is the first mono-specific (Cibicidoides mundulus) record for the North Atlantic. In general, δ18O values are characterized by a longterm trend towards decreasing values reflecting either higher bottom-water temperatures or less ice volume over the studied time interval. Superimposed on this general trend are short-term fluctuations, most probably reflecting obliquity-modulated glacial/interglacial cycles. Thereby, one interval between approx. 128 and 123 m CCSF stands out as being fundamentally different. A close-up of this specific interval reveals that each cycle is characterized by a slow increase of benthic foraminiferal δ18O values followed by a rapid decrease. This pattern is fundamentally different from the U-like shape of other glacial cycles within the record but conspicuously reminiscent of the saw-tooth nature of Late Pleistocene glacial/interglacial cycles. In order to tackle research question 3, samples from the expanded Oligocene to early Miocene succession at Site U1405 were used to investigate exquisitely preserved planktic foraminifera with coupled δ18O and Mg/Ca analyses. These data suggest a cooler surface-water mass that characterizes the OMT at the study site, interpreted to reflect a southward extension of the (proto-) Labrador Current. The new δ18Osw record supports this scenario. After the OMT, surface-ocean temperatures returned almost to pre-OMT values, suggesting that the influence of the (proto-) Labrador Current retreated and that the study site was situated in Gulf Stream waters, as it is the case today.
Publications
- (2016). Data report: relative abundance of benthic foraminiferal morphotypes across the Eocene/Oligocene and Oligocene/Miocene boundaries (IODP Expedition 342 Site U1406, North Atlantic) Proc. IODP 342
K. Moriya and O. Friedrich
(See online at https://doi.org/10.2204/iodp.proc.342.204.2016) - Data report: revised composite depth scale and splice for IODP Site U1406. Proc. IODP 342
T.E. van Peer, D. Liebrand, C. Xuan, P.C. Lippert, C. Agnini, N. Blum, P. Blum, S.M. Bohaty, P.R. Bown, R. Greenop, W.E.C. Kordesch, D. Leonhardt, O. Friedrich and P.A. Wilson
(See online at https://doi.org/10.2204/iodp.proc.342.202.2017)
