Assessment of Chronological Records of Rare Earth Elements in Sidi Moussa Lagoon Sediment (North-Western Morocco)

Abstract

Rare Earth Elements and yttrium (REEs+Y) were measured by inductively Coupled Plasmas -Mass Spectrometry in two previously dated sediment cores collected from Sidi Moussa lagoon, located in the Moroccan Atlantic coast, in order to establish the historical inputs of these elements and to determine the contribution of anthropogenic activities. In an attempt to clarify the phase associations of REE+Y, the Ce anomaly profiles were partitioned into three parts: the upper part with negative anomalies, except for a positive Ce/Ce* peak in 1983, the middle part with positive anomalies rising to high Ce/Ce*, and the lower part with also fairly increasing positive anomalies. Pearson correlations were calculated between REE+Y and major elements (Mn, Fe and Al) in different parts of Core-1. REE+Ys, except for Pr, were significantly correlated only with Mn, which suggests that the associated phase in the upper part consists of Mn oxides. The central part is characterized by a negative correlation of REE+Y with Mn and a positive correlation with Fe. The maximal concentrations were observed in two horizons in the sediment cores being attributed to both natural and industrial sources. The association of REEs with manganese oxides, iron-rich minerals and detritus material was changing in different parts of the cores. Only in specific layers, all REEs were weakly to moderately enriched, while yttrium was moderately to strongly enriched. The notable reduction in the upper layers is a reflection of the environmental management plan implemented by the phosphate company and the change in the morphology of the lagoon, which has reduced communication with the ocean.