The million-year variability of the marine nitrogen cycle is poorly understood. Before 57 million years (Ma) ago, the N-15/N-14 ratio (delta N-15) 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, delta N-15 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-depthwater forming along the Tethys Seamargins may have caused the expanded suboxia, ending with the collision. From 50 to 35 Ma ago, delta N-15 was lower than modern values, suggesting widespread sedimentary denitrification on broad continental shelves. delta N-15 rose at 35 Ma ago, as ice sheets grew, sea level fell, and continental shelves narrowed.
1.Princeton Univ, Dept Geosci, Princeton, NJ 08540 USA 2.Univ Calif Berkeley, Dept Earth & Planetary Sci, Berkeley, CA 94720 USA 3.Lawrence Berkeley Natl Lab, Earth & Environm Sci Area, Berkeley, CA 94720 USA 4.Max Planck Inst Chem, Dept Climate Geochem, D-55128 Mainz, Germany 5.Swiss Fed Inst Technol, Dept Earth Sci, CH-8092 Zurich, Switzerland 6.Natl Taiwan Univ, Res Ctr Future Earth, Taipei 106, Taiwan 7.CALTECH, Div Geol & Planetary Sci, Pasadena, CA 91125 USA
Recommended Citation:
Kast, Emma R.,Stolper, Daniel A.,Auderset, Alexandra,et al. Nitrogen isotope evidence for expanded ocean suboxia in the early Cenozoic[J]. SCIENCE,2019-01-01,364(6438):386-+