The biogeochemical cycling of bio-essential trace elements in coastal seawater regulates their fluxes to the open ocean hence influencing the marine primary production. In this study, the behaviors of dissolved trace elements, Rare Earth Elements (REEs), and humic dissolved organic matters (DOM_H) of terrestrial versus marine origins were investigated in the surface waters of two coastal regions in Korea. Despite the occurrence of intensive scavenging processes revealed by the REE behaviors and rapid removal of particle-reactive ²³⁴Th as well as significant biological removal processes, our results showed that both terrestrial and marine origins of DOM_H would associate with dissolved trace elements, especially with Mn, Fe, and Cu, which would protect these elements from being removed by particle scavenging or biological uptake. This association process could result in a longer residence time for these trace elements in the water columns, hence travelling longer distances. Moreover, this study discovers that the stabilization of trace elements by different sources of DOM_H could be variable depending on the biogeochemical processes. Thus, the association of trace elements with DOM_H seems to play a key role in the shuttling of bio-essential trace elements to the open ocean via coastal oceans.

humic substances, scavenging, trace elements, coastal ocean