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Nitrogen isotope evidence for expanded ocean suboxia in the early Cenozoic

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Science  26 Apr 2019:
Vol. 364, Issue 6438, pp. 386-389
DOI: 10.1126/science.aau5784

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Circulation more than temperature

Changes in continental configuration and sea level affected the ocean's oxygen levels and the rate of denitrification between 70 and 30 million years ago. That finding by Kast et al. shows a fundamental difference from the modern ocean, in which the extent of suboxia is controlled primarily by global temperature. Changes in the nitrogen isotopic composition of marine organic matter correlate with the collision of India and Asia and the circulation changes that occurred as a result. Later, isotopic composition changed further in response to a fall in sea level as global cooling caused ice sheets to grow.

Science, this issue p. 386