Fig. 2.

Conceptual model for sedimentary values of in an ocean in which is the dominant fixed N species. (A) System in which the δ¹⁵N values of exported eukaryotic biomass depend on the fractional fluxes to ammonium assimilation (φ₁), oxidation (φ₂), and recycling (φ₃), as well as the difference between the associated fractionation factors ε₁ and ε₂. (B–D) Calculated δ¹⁵N values of sedimentary organic matter as a function of percent export from diazotrophs and fractional fluxes φ₁ and φ₂ for three sets of fractionation factors: (B) ε₁ - ε₂ = -5‰; (C) ε₁ - ε₂ = 5‰; (D) ε₁ - ε₂ = 10‰. (E) Data for for OAE 2 from the literature [11 (red); 16 (blue, Italy; green, England); 17 (yellow); 23 (orange), and this study (gray)], plotted relative to the range of paired values of ε₁ and ε₂ solved with the model, assuming 20% export of diazotrophic biomass (solid lines), as well as an ε₁/ε₂ offset of 10‰ assuming 10% export of diazotrophic biomass (dashed line).