Reinforcing the North Atlantic backbone: revision and extension of the composite splice at ODP Site 982

• Main Authors: A. J. Drury, T. Westerhold, D. Hodell, U. Röhl
• Format: Article
• Language: English
• Published: Copernicus Publications 2018-03-01
• Series: Climate of the Past
• Online Access: https://www.clim-past.net/14/321/2018/cp-14-321-2018.pdf
• ISSN: 1814-9324; 1814-9332

Ocean Drilling Program (ODP) Site 982 represents a key location for understanding the evolution of climate in the North Atlantic over the past 12 Ma. However, concerns exist about the validity and robustness of the underlying stratigraphy and astrochronology, which currently limits the adequacy of this site for high-resolution climate studies. To resolve this uncertainty, we verify and extend the early Pliocene to late Miocene shipboard composite splice at Site 982 using high-resolution XRF core scanning data and establish a robust high-resolution benthic foraminiferal stable isotope stratigraphy and astrochronology between 8.0 and 4.5 Ma. Splice revisions and verifications resulted in  ∼  11 m of gaps in the original Site 982 isotope stratigraphy, which were filled with 263 new isotope analyses. This new stratigraphy reveals previously unseen benthic <i>δ</i>¹⁸O excursions, particularly prior to 6.65 Ma. The benthic <i>δ</i>¹⁸O record displays distinct, asymmetric cycles between 7.7 and 6.65 Ma, confirming that high-latitude climate is a prevalent forcing during this interval. An intensification of the 41 kyr beat in both the benthic <i>δ</i>¹³C and <i>δ</i>¹⁸O is also observed  ∼  6.4 Ma, marking a strengthening in the cryosphere–carbon cycle coupling. A large  ∼  0.7 ‰ double excursion is revealed  ∼  6.4–6.3 Ma, which also marks the onset of an interval of average higher <i>δ</i>¹⁸O and large precession and obliquity-dominated <i>δ</i>¹⁸O excursions between 6.4 and 5.4 Ma, coincident with the culmination of the late Miocene cooling. The two largest benthic <i>δ</i>¹⁸O excursions  ∼  6.4–6.3 Ma and TG20/22 coincide with the coolest alkenone-derived sea surface temperature (SST) estimates from Site 982, suggesting a strong connection between the late Miocene global cooling, and deep-sea cooling and dynamic ice sheet expansion. The splice revisions and revised astrochronology resolve key stratigraphic issues that have hampered correlation between Site 982, the equatorial Atlantic and the Mediterranean. Comparisons of the revised Site 982 stratigraphy to high-resolution astronomically tuned benthic <i>δ</i>¹⁸O stratigraphies from ODP Site 926 (equatorial Atlantic) and Ain el Beida (north-western Morocco) show that prior inconsistencies in short-term excursions are now resolved. The identification of key new cycles at Site 982 further highlights the requirement for the current scheme for late Miocene marine isotope stages to be redefined. Our new integrated deep-sea benthic stable isotope stratigraphy and astrochronology from Site 982 will facilitate future high-resolution late Miocene to early Pliocene climate research.