Influence of dissolved organic matter on rare earth elements and yttrium distributions in coastal waters

Abstract

Data collected during this study indicate that dissolved Y and REE (rare earth element) behaviour can be monitored through shale-normalised ratios. Relationships occurring between these ratios suggest that leaching from lithogenic materials is the main source of REE in the studied area. This process involves riverine detrital matter in the inner area of the Gulf of Palermo. Features of shale-normalised patterns and the relationship recognised between dissolved Fe and Y/Ho suggest that REE are released from Fe-rich coatings of atmospheric dust. Observed similarities between dissolved Fe and chlorophyll-α content suggest that leaching of Fe-rich atmospheric particulates induces a fertilisation of shallow water layers influencing the dissolved organic content. In turn, the increasing chlorophyll-α content causes a progressive decrease in amplitude of the negative Ce anomaly in seawater that is also observed in water in the Central Mediterranean Sea, suggesting that organic matter generally plays a key role in REE behaviour at the solid–liquid interface. Shale-normalised REE features recognised in suspended particulate matter (SPM) indicate the occurrence of three different fractions from lithogenic matter, biogenic carbonates and authigenic components, respectively. The latter is formed during REE scavenging onto the surface of detrital biogenic particles and is mainly recognised in inner gulf waters.

Keywords:

• rare earth elements
• chlorophyll-α
• Ce anomaly
• Mediterranean Sea

Acknowledgements

This work was supported by PROREPLUS ALIF (lAboratori di testing per dispositivi eLettroacustici, sensorI oceanograFici e metodologie finalizzati al monitoraggio dello stato delle risorse biologiche del mare) and ICT-3E funds from CIPE (Italy) and the Italian National Research Council (CNR). We wish to thank the R/V Urania crew for helping us during the sampling cruise. Moreover, the authors are very grateful to Rosa Cidu and two anonymous reviewers for their careful and dedicated job of critical revision of a first version of the manuscript.