Nitrogen isotope evidence for expanded ocean suboxia in the early Cenozoic

Kast, Emma R., Stolper, Daniel A., Auderset, Alexandra, Higgins, John A., Ren, Haojia, Wang, Xingchen T., Martínez-García, Alfredo, Haug, Gerald H. and Sigman, Daniel M. (2019) Nitrogen isotope evidence for expanded ocean suboxia in the early Cenozoic. Science, 364 (6438), 386-389. (doi:10.1126/science.aau5784).

Abstract

The million-year variability of the marine nitrogen cycle is poorly understood. Before57 million years (Ma) ago, the15N/14Nratio(d15N) of foraminifera shell-bound organicmatter from three sediment cores was high, indicating expanded water column suboxiaand denitrification. Between 57 and 50 Ma ago,d15N declined by 13 to 16 per mil in theNorth Pacific and by 3 to 8 per mil in the Atlantic. The decline preceded global coolingand appears to have coincided with the early stages of the Asia-India collision. Warm, saltyintermediate-depth water forming along the Tethys Sea margins may have caused the expandedsuboxia, ending with the collision. From 50 to 35 Ma ago,d15N was lower than modern values,suggesting widespread sedimentary denitrification on broad continental shelves.d15Nroseat35 Ma ago, as ice sheets grew, sea level fell, and continental shelves narrowed

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Contributors

Author: Alexandra Auderset

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