Coupled isotopic systematics of surface cerium and neodymium in the Pacific Ocean

<jats:p>Trace metals are known to be essential elements in marine ecosystems. Radiogenic isotopes of neodymium (Nd) have been used as tracers in many recent oceanic trace metal studies, although, among rare earth elements, cerium (Ce) isotopes might be an interesting complementary tracer for particle reactive and lithogenic metals such as manganese. This study determined the <jats:sup>138</jats:sup>Ce/<jats:sup>142</jats:sup>Ce ratios in surface waters of the Pacific Ocean and its surrounding marginal seas: the Sulu Sea, the South China Sea, the East China Sea, and the South Australian Basin. The <jats:sup>138</jats:sup>Ce/<jats:sup>142</jats:sup>Ce and <jats:sup>143</jats:sup>Nd/<jats:sup>144</jats:sup>Nd data are discussed in terms of the sources of rare earth elements and elemental fractionation between Ce and Nd in the marine environment. In the Western North Pacific Central Water, East China Sea, and South China Sea, isotopic compositions of Ce (ɛ<jats:sub>Ce</jats:sub> = +0.7 to 1.4) are most affected by radiogenic Ce of continental origin. In contrast, less radiogenic isotopic compositions of Ce (ɛ<jats:sub>Ce</jats:sub> = −0.4 to +0.3) in the Pacific Equatorial Water were observed locally near volcanic islands such as New Guinea Island, suggesting the influence of mantle‐derived Ce. Compared with Nd, the isotopic composition of Ce showed a heterogeneous distribution in a given surface water mass, reflecting the importance of local sources. Variations of isotopic compositions and concentrations of Ce in the western Equatorial Pacific and the East China Sea suggest that lithogenic Ce is supplied and scavenged by particle‐dissolved interaction near the margins. Radiogenic Ce in the Western North Pacific Central Water, which is more continental‐like than Nd isotopes, suggests direct input by atmospheric dust into the North Pacific Ocean. The isotopic distribution of Ce is sensitive to aeolian supply to the surface waters of the open ocean. This unique feature indicates that the <jats:sup>138</jats:sup>Ce/<jats:sup>142</jats:sup>Ce ratio can be a useful chemical tracer for lithogenic trace elements such as iron and manganese, which have short oceanic residence time.</jats:p>