[BCG06-02] Fish debris and rare-earth deposition caused by topographically induced upwelling in the latest Eocene
Keywords:Fish skeletal debris, Rare-earth elements, Osmium isotope
In 2013, a deep-sea sediment extremely enriched in fish skeletal debris and rare earth elements was found in western North Pacific [2,3]. The maximum contents of fish debris and rare earth elements were reported to be ~30% and ~7000 ppm, respectively [2,3]. To unravel the causes of the anomalous accumulation of fish debris and rare earth elements, we determined the depositional age of this fish debris-rich sediment based on osmium isotope stratigraphy. Depositional ages of sediment samples can be obtained by comparing the measured osmium isotope ratios (187Os/188Os) in the samples with the reconstructed seawater 187Os/188Os curve .
Our osmium isotope measurement and age assignment revealed that the deposition of the fish debris-rich sediment was contemporaneous with the first appearance of the Antarctic ice-sheet in the latest Eocene. At this time, the ice-sheet cooled high southern latitude and could have invigorated Antarctic bottom water formation . The enhanced northward flow of bottom water would have stirred nutrient-rich deep ocean and led to nutrient upwelling on topographic barriers such as seamounts , which resulted in flourishment of pelagic organisms
including fish. Consequently, an anomalous amount of fish debris has deposited and now constitutes a huge storehouse for rare-earth elements.
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