Radiocarbon Dating of Marine Shells from the Gulf of Cadiz: The marine radiocarbon reservoir effect, its variability during the Holocene and palaeoenvironmental inferences.

Abstract

The ocean reservoir is deficient in radiocarbon compared with the atmosphere and, consequently, an offset in 14C age exists between coeval samples containing marine carbon versus those containing terrestrial carbon. A record of past reservoir ages is preserved in the 14C ages of contemporary marine and terrestrial material. The quantification of the marine radiocarbon reservoir effect (ΔR) is of crucial importance to the correct calibration of the 14C ages of marine samples. For the southern Atlantic Iberian coast, for the last 3000 yr, ΔR takes the following values +69±17 14C yr (Barlavento coast), -26±14 14C yr (Sotavento coast), and -108±31 14C yr (Andalusian coast), which are in accordance with the oceanographic conditions present in each area. Results also suggest that during the 5th millennium cal BP very different oceanographic conditions (high positive ΔR values) prevail in the Barlavento and in the Atlantic Andalusian coastal areas and, consequently, in all the northern Gulf of Cadiz region, perhaps due to the extension of the Azores Front eastward along the Azores Current penetrating into the Gulf of Cadiz.