Study on vertical profiles of rare earth elements by using an ocean general circulation model

Abstract

Observed vertical profiles of rare earth elements (REEs) in the North Pacific Ocean show a systematic change from lighter to heavier REEs. Their source and sink consist of external fluxes coming from the surface and the bottom of the ocean and internal recycling within the ocean. In order to evaluate the role of each source and sink in controlling the vertical profiles of REEs, we conduct numerical simulations of REEs by using an ocean general circulation model. These simulations demonstrate that the shape of their vertical profiles is not directly related to the external sources from river runoff, atmospheric dust deposition, and coastal regions but is sensitive to the internal recycling processes within the ocean. Nutrient‐like treatment where REEs are removed at the surface and released in the deep ocean is suitable for simulating the vertical profiles of lighter REEs but not for heavier REEs. When the irreversible scavenging is considered as a sink term and particle dissolution is taken into consideration as a source term, the vertical profiles of heavier REEs can be reproduced but those of lighter REEs cannot. The observed difference in the vertical profiles among REEs can be reproduced only when the reversible scavenging process is incorporated into the model. Only the reversible scavenging process accounts for the observed vertical profiles of different REEs in comprehensive manner.