Nitrogen isotope evidence for expanded ocean suboxia in the early Cenozoic
Abstract
The million-year variability of the marine nitrogen cycle is poorly understood. Before 57 million years (Ma) ago, the ^(15)N/^(14)N ratio (δ^(15)N) of foraminifera shell-bound organic matter from three sediment cores was high, indicating expanded water column suboxia and denitrification. Between 57 and 50 Ma ago, δ^(15)N declined by 13 to 16 per mil in the North Pacific and by 3 to 8 per mil in the Atlantic. The decline preceded global cooling and appears to have coincided with the early stages of the Asia-India collision. Warm, salty intermediate-depth water forming along the Tethys Sea margins may have caused the expanded suboxia, ending with the collision. From 50 to 35 Ma ago, δ^(15)N was lower than modern values, suggesting widespread sedimentary denitrification on broad continental shelves. Δ^(15)N rose at 35 Ma ago, as ice sheets grew, sea level fell, and continental shelves narrowed.
Additional Information
© 2019 American Association for the Advancement of Science. Received 6 August 2018; accepted 26 March 2019. We thank S. Oleynik, A. Weigand, B. Hinnenberg, and F. Rubach for laboratory support and expertise, and P. Mateo for advice on foraminifera picking. This research used samples and/or data provided by the Ocean Drilling Program (ODP) and the International Ocean Discovery Program (IODP). The manuscript was improved by comments from three anonymous reviewers This work was supported by U.S. NSF grants OCE-1060947, 0960802, and 1136345 (D.M.S.) and by the Max Planck Society (G.H.H.); E.R.K. received support from the Tuttle Fund of the Department of Geosciences, Princeton University; D.A.S. was supported by the NOAA Climate and Global Change Postdoctoral Fellowship. Author contributions: D.A.S., D.M.S., and J.A.H. conceptualized the study; E.R.K. and D.A.S. carried out the nitrogen isotope measurements; A.A. and A.M.-G. carried out the TEX_(86) measurements; X.T.W. and H.R. provided methodology and training; E.R.K., D.A.S., J.A.H., and D.M.S. performed data analysis; E.R.K. and D.M.S. prepared the manuscript with input from all authors. The authors have no competing interests to declare. Data and materials availability: All data are available in the manuscript or the supplementary materials.Attached Files
Supplemental Material - aau5784_DataS1.xlsx
Supplemental Material - aau5784_DataS2.xlsx
Supplemental Material - aau5784_Kast_SM.pdf
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Additional details
- Eprint ID
- 94978
- Resolver ID
- CaltechAUTHORS:20190425-133429105
- OCE-1060947
- NSF
- OCE-0960802
- NSF
- OCE-1136345
- NSF
- Max Planck Society
- Princeton University
- National Oceanic and Atmospheric Administration (NOAA)
- Created
-
2019-04-25Created from EPrint's datestamp field
- Updated
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2021-11-16Created from EPrint's last_modified field