A New Seismic Stratigraphy in the Indian-Atlantic Ocean Gateway Resembles Major Paleo-Oceanographic Changes of the Last 7 Ma

The Expedition 361 Scientists

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Abstract

The exchange of water masses between the Indian Ocean and the Atlantic constitutes an integral interocean link in the global thermohaline circulation. Long-term changes in deep water flow have been studied using seismic reflection profiles but the seismic stratigraphy was poorly constrained and not resolved for the time period from the late Miocene onward. Here we present results from International Ocean Discovery Program Site U1475 (Agulhas Plateau) located over a sediment drift proximal to the entrance of North Atlantic Deep Water into the Southern Ocean and South Indian Ocean. Site U1475 comprises a complete carbonate-rich stratigraphic section of the last ~7 Ma that provides an archive of climate-induced variations in ocean circulation. Six marker reflectors occurring in the upper 300 m of the drift are identified here for the first time. The formation of these reflectors is mainly due to density changes that are mostly caused by changes in biogenic versus terrigenous sediment deposition. Synthetic seismograms allow age assignments for the horizons based on biostratigraphy and magnetostratigraphy. Prominent reflectors are related to late Pleistocene glacial/interglacial variability, the middle and early Pleistocene transitions, and the onset of the northern hemisphere glaciation. A peculiar early Pliocene interval (~5.3–4.0 Ma) bounded by two reflectors is characterized by fourfold elevated sedimentation rates (>10 cm/kyr) and the occurrence of sediment waves. We argue that this enhanced sediment transport to the Agulhas Plateau was caused by a reorganization of the bottom current circulation pattern due to maximized inflow of North Atlantic Deep Water.

Original languageEnglish
Pages (from-to)339-358
Number of pages20
JournalGeochemistry, Geophysics, Geosystems
Volume20
Issue number1
Early online date21 Dec 2018
DOIs
Publication statusPublished - Jan 2019

Funding

1Alfred‐Wegener‐Institut, Helmholtz‐Zentrum für Polar‐ und Meeresforschung, Bremerhaven, Germany, 2Japan Agency for Marine‐Earth Science and Technology (JAMSTEC), Institute of Biogeosciences, Yokosuka, Japan, 3Now at Instituto Andaluz de Ciencias de la Tierra CSIC, Universidad de Granada, Armilla, Spain, 4Ice Core Laboratory, National Centre for Antarctic and Ocean Research (NCAOR), Vasco da Gama Goa, India, 5Department of Earth Sciences, Cardiff University, Main College, Cardiff, UK, 6Lamont‐Doherty Earth Observatory, Columbia University, Palisades, NY, USA, 7International Ocean Discovery Program, Texas A&M University, College Station, TX, USA, 8See Appendix A2 We acknowledge the work of the crew, technicians, and scientific staff of IODP Expedition 361. This research used samples and data provided by the International Ocean Discovery Program (IODP). Funding was provided by the Deutsche Forschungsgemeinschaft (DFG) under contract Ue 49/17. Comments by Andrew Green and an anonymous reviewer greatly improved our manuscript. The data reported here are available through the Pangaea database (https://doi.org/10.1594/ PANGAEA.896810).

FundersFunder number
International Ocean Discovery Program
Natural Environment Research CouncilNE/P000037/1
Deutsche ForschungsgemeinschaftUe 49/17

    Keywords

    • Agulhas Plateau
    • contourites
    • physical properties
    • seismic reflection method

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