Fish proliferation and rare-earth deposition by topographically induced upwelling at the late Eocene cooling event : Assistant Professor Junichiro Ohta, Frontier Research Center for Energy and Resources, Lecturer Kazutaka Yasukawa, Frontier Research Center for Energy and Resources, Kazuhide Mimura(D3), Department of Systems Innovation, Associate Professor Kentaro Nakamura, Department of Systems Innovation, Professor Yasuhiro Kato, Frontier Research Center for Energy and Resources, and other researchers.

Authors
Junichiro Ohta, Kazutaka Yasukawa, Tatsuo Nozaki, Yutaro Takaya, Kazuhide Mimura, Koichiro Fujinaga, Kentaro Nakamura, Yoichi Usui, Jun-Ichi Kimura, Qing Chang, Yasuhiro Kato

Abstract
The deep-sea clay that covers wide areas of the pelagic ocean bottom provides key information about open-ocean environments but lacks age-diagnostic calcareous or siliceous microfossils. The marine osmium isotope record has varied in response to environmental changes and can therefore be a useful stratigraphic marker. In this study, we used osmium isotope ratios to determine the depositional ages of pelagic clays extraordinarily rich in fish debris. Much fish debris was deposited in the western North and central South Pacific sites roughly 34.4 million years ago, concurrent with a late Eocene event, a temporal expansion of Antarctic ice preceding the Eocene–Oligocene climate transition. The enhanced northward flow of bottom water formed around Antarctica probably caused upwelling of deep-ocean nutrients at topographic highs and stimulated biological productivity that resulted in the proliferation of fish in pelagic realms. The abundant fish debris is now a highly concentrated source of industrially critical rare-earth elements.

Scientific Reports : https://www.nature.com/articles/s41598-020-66835-8