Fig. 3: Evolutionary history of marine nitrogen cycling.
From: Expanded subsurface ocean anoxia in the Atlantic during the Paleocene-Eocene Thermal Maximum
a Histogram of compiled sedimentary and foraminifera-bound δ15N data. Dashed lines represent mean δ15N values of modern dissolved inorganic nitrogen (DIN), modern coretop and Cretaceous oceanic anoxic event 2 (OAE2) bulk sediments, and Paleocene-Eocene Thermal Maximum (PETM) and pre-PETM symbiont-bearing planktic foraminifera from this study and previously published data17,32,36. b Box-model estimations of mean ocean fixed nitrogen δ15N. The contour of mean ocean δ15N is generated as a function of sedimentary denitrification and ammonium-type oxygen-deficient zones (ODZs) nitrogen loss with weak isotope fractionation effects (εN/D) of 2‰ (solid lines) and 10‰ (dashed lines). Colored star symbols indicate the reconstructed mean ocean δ15N values from (a) when εN/D = 2. c The response of nitrogen and sulfur cycles to oceanic oxygen change in the South Atlantic across the PETM. Oxygen decline (green line) from oxic ([O2] > 5 μmol/kg) to suboxic (0 < [O2] < 5 μmol/kg; blue shaded boxes) to anoxic ([O2] = 0 μmol/kg; red shaded boxes) and recovery in ODZs through time results in δ15N (blue line) and δ34S (red line) anomalies.
