Role of terrestrial versus marine sources of humic dissolved organic matter on the behaviors of trace elements in seawater

Abstract

We investigated the behaviors of dissolved trace elements (Mn, Fe, Ni, Cu, Zn, and Cd) associated with humic dissolved organic matter (DOMH) of varying origins in the surface waters of two Korean coastal regions (Jinhae Bay [JH] and offshore Tongyeong [TY]). Both regions displayed intensive scavenging and settling of the particle-reactive Ce and 234Th tracers. However, in JH, where DOMH is mainly terrestrial-derived, the concentrations of trace elements (Fe, Ni, and Cu) were negatively correlated with salinity and positively correlated with DOMH. This indicates that terrestrial DOMH could form complexes with dissolved trace elements, and this complexation likely deters the adsorptive removal of trace elements by settling particles. Similar interactions between trace elements (Mn, Fe, and Cu) and DOMH were also discovered in TY, where most DOMH originated from marine biological production. Our study reveals that both terrestrial and marine DOMH would complex with dissolved trace elements, stabilizing them in the dissolved phase in coastal waters. Therefore, DOMH-trace element complexation in coastal waters could play a key role in regulating the cycling and transport of trace elements in the ocean.