Simulation of global distribution of rare earth elements in the ocean using an ocean general circulation model

In this study, we report our ocean general circulation model simulations of the global distribution of rare earth elements (REEs) in the ocean. As previously reported (Oka et al. in Glob Biogeochem Cycles 23:1–16, 2009), the vertical profiles of REEs in the North Pacific Ocean are strongly controlled by the reversible scavenging process, and the systematic differences between REEs can be reproduced in the model by selecting an appropriate model parameter which controls affinity to particles. We here demonstrate that the external REE input from the coastal regions also plays a role in controlling the vertical profiles of dissolved REE and their inter-basin differences. The role of the external inputs is especially important for light REEs, such as neodymium (Nd). The linear increase in Nd concentration in the North Pacific Ocean cannot be sufficiently reproduced by the reversible scavenging alone; rather, a combination of the reversible scavenging and the external inputs is necessary. On the other hand, the distribution of heavy REEs, such as lutetium (Lu), can be broadly reproduced without the external inputs, suggesting that Lu has similarity with conservative nutrient-like tracer. When compared with REE observations compiled from both the recently obtained GEOTRACES dataset and pre-GEOTRACES reported data, our simulations successfully reproduced the overall features of these observations. Observational data suggested that the vertical profiles of REEs are not the same among the basins; our model simulations demonstrate that this feature can be clearly reproduced by considering both the reversible scavenging and the external REE inputs from the coastal regions.