Stratigraphic variations of fe–mn micronodules and implications for the formation of extremely rey-rich mud in the western north pacific ocean

Kazutaka Yasukawa, Satoshi Kino, Junichiro Ohta, Keishiro Azami, Erika Tanaka, Kazuhide Mimura, Koichiro Fujinaga, Kentaro Nakamura, Yasuhiro Kato*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


The origin of deep-sea sediments in the western North Pacific Ocean, which are significantly enriched in rare-earth elements and yttrium (REY), and its paleoceanographic implications have been poorly constrained. Here, we investigated stratigraphic variations in the chemical compositions and textures of ferromanganese (Fe–Mn) micronodules separated from western North Pacific sediments. The characteristics of the micronodules of an extremely REY-rich mud layer vary from almost purely diagenetic to relatively hydrogenetic. This indicates the abundant supply of organic matter to the sediment together with fish debris that accumulates REY at the onset of the REY-enrichment of the mud, followed by the exposure of the seafloor to oxic water masses during the latter half of the formation of the REY-rich mud. These results support a previously proposed formation mechanism based on which enhanced bottom water currents caused pelagic fish proliferation via the upwelling of nutrients and fish debris was physically sorted and selectively accumu-lated on the seafloor. After the main REY-enrichment, the micronodules exhibit varying diagenetic signatures, suggesting changes in the bottom current intensities after the main REY-enrichment. However, the bulk REY contents do not increase. This implies that a sufficient increase in the fish productivity is an essential factor affecting the formation of REY-rich mud.

Original languageEnglish
Article number270
Pages (from-to)1-20
Number of pages20
Issue number3
Publication statusPublished - 2021 Mar
Externally publishedYes


  • Bottom water current
  • Deep-sea sed-iment
  • Ferromanganese micronodule
  • Minamitorishima Island
  • Pacific Ocean
  • REY-rich mud
  • Seafloor mineral resources

ASJC Scopus subject areas

  • Geotechnical Engineering and Engineering Geology
  • Geology


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