Nitrogen isotope evidence for expanded ocean suboxia in the early Cenozoic
"The million-year variability of the marine nitrogen cycle is poorly understood. Before 57 million years (Ma) ago, the 15N/14N ratio (δ15N) of foraminifera shell-bound organic matter from three sediment cores was high, indicating expanded water column suboxia and denitrification. [...]"
Authors: Emma R. Kast et al.