Trace metal biogeochemistry affects marine primary productivity. For example, insufficient supply of iron has been shown to limit phytoplankton growth in large area of surface ocean, whilst copper could be toxic at higher concentrations. The bioavailability of trace metals is determined by its chemical speciation, which in turn is dependent on the physico-chemical properties (pH, temperature, salinity) of the water. Nevertheless, metal speciation, which is strongly influenced by binding sites in dissolved organic matter (DOM), is still operationally determined, resulting in empirical parameters that are difficult to use in a predictive capacity. Here we outline an approach for predicting trace metal speciation that is based on determination of intrinsic DOM-trace metal binding properties that are independent of pH, temperature and salinity. We determine the competitive interactions between an ion exchange resin, DOM, the hydrogen cation and trace metals in seawater via inductively coupled plasma mass spectrometry. We firstly investigated reproducibility and required equilibration times for our multifactorial titration experiments. Then, we combined with an ion paring-organic matter (NICA-Donnan) model, and finally show how results of these experiments can be used to derive intrinsic constants for predicting DOM-trace metal interactions in seawater. We aim to obtain a comprehensive assessment of trace metal biogeochemistry in the context of warming and acidifying ocean.

trace elements, dissolved organic matter (DOM), ocean acidification