Regional geochemical baselines for Portuguese shelf sediments

Area of Science:

• Environmental Geochemistry
• Marine Geology

Background:

• Historical sediment data from the 1970s provides a baseline for metal concentrations.
• Portuguese shelf sediments exhibit distinct oceanographic and sedimentological characteristics between the western and Algarve coasts.

Purpose of the Study:

• To assess metal concentrations (Al, Cr, Cu, Ni, Pb, Zn) in Portuguese shelf sediments.
• To establish regional geochemical baselines (RGB) and identify anthropogenic metal enrichments.
• To compare metal distributions in sediments from the 1970s with recent samples from 2002.

Main Methods:

• Analysis of archived DGM-INETI sediment data from 267 sites (1970s).
• Definition of regional geochemical baselines (RGB) using aluminum as a reference element.
• Superposition of 2002 seabed samples onto RGB models to detect metal enrichments.
• Calculation of enrichment factors (EF) to quantify metal anomalies.

Main Results:

• Regional geochemical baselines were established for western and Algarve shelf segments.
• Three samples near the Tejo River showed anthropogenic metal enrichment (EF(Pb)<3, EF(Zn)<4).
• Most other studied areas exhibited enrichment factors close to 1, indicating natural metal origins.

Conclusions:

• Sediment metal distributions on the Portuguese shelf are largely natural.
• Minor anthropogenic metal inputs were detected near the Tejo River.
• Historical data analysis is crucial for understanding long-term environmental changes in marine sediments.