Application of transition metal isotope tracers in global change research

High-precision isotope composition determinations using multicollector, magnetic-sector inductively coupled plasma mass spectrometry (MC-ICPMS) have recently revealed that some transition metal isotopes such as those of Mo, Fe, Cu, Zn etc. can be used as biogeochemical tracers in global change research. The Mo isotope system may be useful in paleoredox investigations indicating that δ97/95Mo in seawater may co-vary with changes in the relative proportions of anoxic and oxic sedimentation in the ocean, and that this variation may be recorded in δ97/95Mo of anoxic sediments. The Mo continental flux into the oceans and the global Mo isotope budget can be estimated from δ97/95Mo values. The Fe isotope composition in seawater is an important issue because Fe plays a controlling role in biological productivity in the oceans and its abundance in seawater may have substantial effect on climate changes. Iron isotope fractionations could result from bio- and abio-processes and have about 0.1% variation (δ56/54Fe), so Fe isotopes considered alone cannot be used to distinguish the products of abiotic and biotic Fe processing in geological records. Cu and Zn isotopes are also used as biogeochemical tracers, but the researches are relatively less. This review mainly focuses on the methods for preparation, purification and determination, of new isotope tracer samples, and on isotope applications in marine environmental changes.