Journal of Oceanography, Vol. 62 (No. 4), pp. 441-455, 2006
Yayoi Hongo1,2*, Hajime Obata1, Dia Sotto Alibo3 and Yoshiyuki Nozaki1
1Ocean Research Institute, The University of Tokyo, Nakano-ku, Tokyo 164-8639, Japan
2Molecular Characterization Team, Advanced D&S Center, RIKEN (The Institute of Physical and Chemical Research), Hirosawa, Wako, Saitama 351-0198, Japan
3Chemistry Department, University of San Carlos, Cebu City 6000, Philippines
(Received 24 August 2005; in revised form 11 December 2005; accepted 24 January 2006)
Abstract: The concentration of dissolved rare earth elements (REE) were determined at 47 stations in the North Pacific surface waters. Combining with other previous data, we present the surface REE distribution in the North Pacific and discuss the controlling factors. The surface concentrations increase toward the high latitude and continental margin (e.g. [Nd] > 10 pmol kg-1) from the central North Pacific (e.g. [Nd] < 5 pmol kg-1). The North Pacific Deep Water-normalized REE patterns are varied, indicating that two or more factors contribute to the REE distribution. We examined four factors making the regional variation of surface REE concentrations mainly; a) particle scavenging, b) atmospheric dust input, c) vertical mixing and d) lateral transport from the coastal region. Flux calculations for Nd showed that the influence of atmospheric dust was less significant than the vertical input even in the western upwelling zone. Moreover, the longitudinal and latitudinal transitions of surface REE seem to reflect the lateral supply from the coastal areas. We constructed the diagram of surface Er/Lu and Er/Yb molar ratios in order to assess the origin and the input processes of the surface REE. Both molar ratios showed increasing trend toward PEW (Er/Lu (>10.5) and Er/Yb (>1.4)) from PSUW (Er/Lu (>7) and Er/Yb (>1.2)). The high Er/Lu and Er/Yb ratios in PEW indicate that the lateral supply of terrestrial materials from the coastal area is possibly the important factor in PEW, because only weathering and dissolution of rocks can explain such high Er/Lu and Er/Yb ratios to our knowledge.