Monsoons, Upwelling, and the Deoxygenation of the Northwestern Indian Ocean in Response to Middle to Late Miocene Global Climatic Shifts

Or M. Bialik, Gerald Auer, Nanako O. Ogawa, Dick Kroon, Nicolas D. Waldmann, Naohiko Ohkouchi

Research output: Contribution to journalArticlepeer-review


Today, upwelling along the Oman margin in the Arabian Sea is governed by the South Asian Monsoon winds. The Oman upwelling results in the formation of an oxygen minimum zone (OMZ) spanning across the Arabian Sea and large parts of the Indian Ocean. While these conditions are recorded as early as the middle Miocene (~15 Ma), the long-term dynamics of upwelling in the Arabian Sea are as of yet poorly constrained during the middle to late Miocene. Here, we use organic and inorganic proxies combined with sedimentary and paleontological records to constrain the evolution of upwelling at Ocean Drilling Program Site 722B between ~15 and ~8.7 Ma. Our record shows that Mn depletion occurred at ~14.5 Ma, likely due to regionally confined OMZ formation at that time. Biogenic silica accumulation intensified between ~12.5 and ~11 Ma. The δ15N values (>6‰) provide evidence for the onset of at least intermittent denitrification between ~11 and ~9.5 Ma during the apex of the global “carbonate crash.” Our data demonstrate that upwelling and OMZ intensity in the Arabian Sea were linked to the reorganization of the Indian Ocean circulation system and South Asian Monsoon during the Miocene. The initiation of these systems occurred once the regional tectonic configuration (i.e., the uplift of the Tibetan Plateau ~25 Ma and the closure of the Tethyan seaway ~20 Ma) was in place. The subsequent development of monsoonal upwelling after 14 Ma responded to latitudinal shifts in climatic belts following the progressive Miocene glaciation of Antarctica.

Original languageEnglish
Article numbere2019PA003762
JournalPaleoceanography and Paleoclimatology
Issue number2
StatePublished - 1 Feb 2020

Bibliographical note

Funding Information:
O. M. B. and G. A. contributed equally and share first authorship. This research used samples and data provided by the International Ocean Discovery Program (IODP). This study was partially funded by GIF project MioEast (Grants 1-1336-301.8/2016) awarded to N. D. W. (in collaboration with Christian Betzler and Martin Frank) and contributes to JSPS Grant 17H07412 awarded to G. A. The authors would like to thank IODP and especially Dr. Lallan Gupta and the Kochi Core Repository (KCC) for access to and diligent sampling of ODP Site 722B. N. Taha, Y. Yoshikawa, and Y. Niyazi are thanked for technical and analytical assistance and Y. Lahan for input regarding oceanic circulation and chlorophyll patterns. We are grateful for the input of 2 anonymous reviewers that help to improve this manuscript. Ellen Thomas and Margret Steinthorsdottir are thanked for their editorial expertise and handling of this manuscript. The data generated for Site 722 presented in this study are available on PANGAEA, doi: 10.1594/PANGAEA.910897 (Diatom and nannofossil counts); 10.1594/PANGAEA.910900 (XRF data); 10.1594/PANGAEA.910901 (OM stable isotopes); and 10.1594/PANGAEA.910902 (Age model).

Publisher Copyright:
© 2020. The Authors.


  • Arabian Sea
  • ODP Site 722
  • OMZ
  • South Asian Monsoon
  • oceanic reorganization
  • upwelling

ASJC Scopus subject areas

  • Oceanography
  • Atmospheric Science
  • Paleontology


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