Influence of diagenetic processes and terrestrial/anthropogenic sources in the REE contents of the Cascais submarine canyon (Iberian western coast)

Highlights: • REE contents were measured in two sediment cores of the Cascais submarine canyon (CSC). • PAAS-normalized REE patterns show input of Tagus contaminated sediment at the CSC shallower site. • Influence of diagenetic processes is reflected in the LREE signal at the deeper site. • The signature of anthropogenic Pb and Hg contamination is clearer in CSC than that of REE. • REE cannot be considered as contaminants of emerging concern in the CSC sediments. Temporal variations of rare earth elements (REE) and their fractionation patterns, major elements, Pb and Hg were determined in two multicores collected at 445 and 2100 m water depth (mwd) in the Cascais submarine canyon (CSC). The PAAS-normalized REE patterns suggest mixing of Tagus estuarine and marine sediments, marked by MREE (Nd‐Dy series) enrichment and by positive Eu-anomaly, with marine sediments. The positive Eu/Eu* implies incorporation of detrital feldspar minerals derived from the estuary. Ce/Ce*, (La/Yb)_PAAS and (Nd/Yb)_PAAS show differences between the two cores. Core 252-35 from the shallower site is enriched in HREE (Ho‐Lu series) over LREE (La‐Pr series), a pattern also found in the Tagus estuary in the vicinity of an abandoned chemical complex, where the environment is affected by the legacy of massive-sulfide ores processing. There seems to be only limited down-canyon sediment transport to the deeper reaches where core 252-32 was collected. This deeper site shows Ce/Ce* peaks coinciding with low (La/Yb)_PAAS values suggesting preferential diagenetic remobilization of LREE relative to HREE. Upcore Pb/Al and Hg/C_org trends observed in both cores indicate dispersion of the anthropogenic component from the estuary through the CSC, which is less obvious from the ∑REE/Al trends particularly in the deeper site. This may suggest the influence of diagenetic processes in the REE signal, associated with relatively low sediment accumulation rates.