Fingerprinting the climatic heartbeat of the late Miocene

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Author(s): Drury, Anna Joy; Westerhold, Thomas; Hodell, David; Palike, Heiko; Rochholz, Fiona; Liebrand, Diederik; Tao, Ze; Minton, Paul; Wade, Bridget; Wilkens, Roy
Author Affiliation(s): Primary:
University of Bremen, MARUM-Center for Marine Environmental Sciences, Bremen, Germany
University of Cambridge, United Kingdom
University College London, United Kingdom
University of Hawaii at Manoa, United States
Volume Title: European Geosciences Union general assembly 2019
Source: Geophysical Research Abstracts, Vol.21; European Geosciences Union general assembly 2019, Vienna, Austria, April 7-12, 2019. Publisher: Copernicus GmbH on behalf of the European Geosciences Union (EGU), Katlenburg-Lindau, Germany. ISSN: 1029-7006
Note: In English
Summary: Accurate stable isotope stratigraphies are fundamental to investigating the influence of orbital forcing on past climate. The global LR04 (Liseicki & Raymo, 2005) and regional Ceara Rise (Wilkens et al., 2017) benthic deep-sea stable isotope stacks have greatly advanced our understanding of Plio-Pleistocene climate dynamics. However, a comparable late Miocene compilation does not exist. Here, we present the first global late Miocene global benthic δ18O and δ13C stacks spanning 8.00-5.33 Ma. The combined chemo- and magneto-stratigraphies from IODP Sites U1337 and U1338 represent a Pacific endmember. We then targeted ODP Sites 982 (N), 926 (E) and 1264 (S) to obtain equivalent Atlantic records. We verified existing splices, generated high-resolution isotope data to fill gaps and extend records to 8.0 Ma, and established independent astrochronologies. This approach was crucial to avoid misalignment and aliasing of short-term excursions, as late Miocene benthic δ18O is notoriously low-amplitude. The new global late Miocene benthic δ18O and δ13C stacks represent a stratigraphic reference section back to 8.00 Ma comparable to LR04. We recognise 68 new δ18O Marine Isotope Stages (MIS) between 7.7 and 6.5 Ma. The benthic δ13C stack shows that the late Miocene carbon isotope shift (LMCIS) actually consists of 4 separate shifts, rather than a single -1 ppm shift: an initial +0.5 ppm shift at 7.9 Ma, followed by three -0.5 ppm shifts at 7.5, 7.1 and 6.7 Ma. These shifts roughly occur every 400 kyr, indicating that eccentricity drove the LMCIS. Between 7.7-6.9 & 6.4-5.4 Ma, there is exceptional agreement between different sites. A strong 40 kyr heartbeat dominates these intervals, marking the initial onset (∼7.7 Ma) and later strengthening (∼6.4 Ma) of the late Miocene 40-kyr world. The 40 kyr rhythm is expressed as asymmetric cycles, indicating that these cycles partially represent ice volume variability. The benthic δ18O stack displays remarkable discordance between 6.9-6.4 Ma, indicating a regionally diverse response to orbital forcing. The Pacific and South Atlantic records are characterised by stable, high δ18O, in contrast to the strong obliquity beat dominating the North Atlantic, indicating this region experienced dynamic climate variability. With these benthic stacks, we have taken a major step towards accurately fingerprinting the deep-sea heartbeat of late Miocene climate. The final puzzle piece remains improved benthic stable isotope stratigraphies spanning 12-8 Ma. Looking forward, we present upcoming work that will complete this process. [Copyright Author(s) 2019. CC Attribution 4.0 License:]
Year of Publication: 2019
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; C-13/C-12; Carbon; Cenozoic; Chemostratigraphy; Climate forcing; Cycles; East Pacific; Expedition 321; Expeditions 320/321; IODP Site U1337; IODP Site U1338; Integrated Ocean Drilling Program; Isotope ratios; Isotopes; Miocene; Neogene; North Pacific; Northeast Pacific; O-18/O-16; Orbital forcing; Oxygen; Pacific Equatorial Age Transect; Pacific Ocean; Paleoclimatology; Stable isotopes; Tertiary; Upper Miocene
Coordinates: N035000 N035000 W1231222 W1231222
N023028 N023028 W1175811 W1175811
Record ID: 2019050540
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from European Geosciences Union, Munich, Germany