Rare earth elements in sediments off Southern California: a new anthropogenic indicator

The rare earth element (REE) composition of dated sediment cores from the San Pedro Shelf (60 m) and the Santa Barbara Basin (588 m) are contrasted. The Santa Barbara Basin cores has relatively uniform REE concentrations throughout it's 60 cm length and a REE composition similar to the crustal abundance. In contrast, the upper 20 cm of the 36 cm deep San Pedro Shelf core is enriched in the concentrations of the light REE (La, Cd, Nd and Sm) but not in the middle REE (Eu) and the heavy REE (Yb, Lu). These upper sediments have a REE signature which is very different from crustal material and which corresponds to anthropogenic inputs beginning in the early 1960's delivered from the Joint Water Pollution Control Plant wastewater outfall located 6 km upcurrent from the San Pedro Shelf Core. The sources of the light REE enrichment are petroleum cracking catalysts and their products; these include emissions, bottom ash, fly ash and wastewater from oil-burning powerplants and oil-refineries. Cracking catalysts are produced from Bastnasite and Monazite, REE ore minerals strongly enriched in light REE. With their unique signature and source, light REE may be a new tool for tracing anthropogenic inputs to themore » Santa Monica and San Pedro Basins.« less