Abstract: This work deals with the microfaunal (benthic foraminifera) and geochemical (trace metals, 14C, 210Pb, 137Cs, and 239/240Pu) study of two boreholes (1200 and 1400 cm length) and three subtidal sediment cores (38?58 cm length) collected in the Pasaia estuary (northern Spain). Foraminiferal assemblages in the Holocene deposits depend on the paleogeographic setting, while different species appear in the Anthropocene sediments as a consequence of the physical transformation of the estuary into an estuarine port. Regarding the geochemical composition, the impact of ancient mining activities (probably of Roman age) can be recognized in the form of peaked values of Pb and Zn. However, older sediments exhibit relatively low contents of trace metals which are conditioned by hydrodynamic patterns and lithogenic inputs. In the Anthropocene record, the influence of these factors is displaced by the decisive role of human activities, as evidenced by the enhanced concentrations of trace metals and the occurrence of artificial radioisotopes and glass microspheres. Additionally, this work provides information about trace metal contamination that may be of interest to corresponding authorities in order to set priorities of action and to take specific measures to prevent further degradation.

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