Fig. 2: Comparison between “nitrate-type” and “ammonium-type” oxygen-deficient zones (ODZs).
From: Expanded subsurface ocean anoxia in the Atlantic during the Paleocene-Eocene Thermal Maximum
a An example depth profile of nitrate-type ODZs with large isotope fractionation effects observed in today’s open-ocean ODZs33. b An example depth profile of ammonium-type ODZs with small isotope fractionation effects observed in the Black Sea34,35. c Schematic of nitrogen cycling in the modern ocean with nitrate-type ODZs. d Schematic of nitrogen cycling in the PETM ocean with nitrate-type and ammonium-type ODZs. Dissolved oxygen levels within ODZs are indicated in color bars. White arrows denote ventilation, and gray arrows denote nitrogen fluxes, with arrow widths indicating flux magnitudes. We note that the deep ocean in the South Atlantic during the PE’TIM was not anoxic, while the modern Black Sea remains euxinic below the euphotic zone.
