SURFACE LAYER ND ISOTOPIC COMPOSITION OF FE-MN CRUSTS COLLECTED FROM THE TAKUYO-DAIGO SEAMOUNT IN THE NORTHWEST PACIFIC REFLECTS AMBIENT SEAWATER
Here we report the first record of surface layer (outermost 0–1 mm) Nd isotopic composition of Fe-Mn crusts collected by ROV from various water depths (1000–5400 m) along the Takuyo-Daigo Seamount in the northwest Pacific, and compare our data with the seawater Nd data previously reported at the near by station, TPS 24 27-1 (24°17.2’N, 150°28.2’E: Piepgras and Jacobsen, 1988).
The samples were collected during three cruises: RV Natsushima NT09-02, RV Kairei KR15-E01, and RV Kairei KR16-01. The topmost surface of each Fe-Mn crust was carefully scraped with a ceramic knife.
The sample was leached with either 2.5 M HCl or 1M HCl with H2O2. Nd was separated and purified from the leachate, and its isotopic composition was determined with the NEPTUNE Plus housed at JAMSTEC, Yokosuka.
We found that the depth profile of ferromanganese crusts is similar to the vertical seawater profile reported for TPS 24 271-1 station. This fact indicates that the surface layers of the Fe-Mn crust reliably reflect seawater values. We conclude that these samples are suitable for determining time-series Nd isotopic data to study ocean circulation of intermediate to deep water masses in the past northern Pacific.