COASTAL UPWELLING AND RADIOCARBONEVIDENCE FOR TEMPORAL FLUCTUATIONS IN OCEAN RESERVOIR EFFECT OFF PORTUGAL DURING THE HOLOCENE

Abstract

This paper focuses on the use of the radiocarbon content of marine shells collected along the Portuguese coast

as a proxy for the intensity of coastal upwelling off of Portugal. Differences in the 14C ages of closely associated marine mollusk

shells and terrestrial material (charcoal or bones) from several Portuguese archaeological contexts seem to be significant

throughout the Holocene. ΔR values range from 940 50 to 160 40 14C yr. Five of these values are significantly higher than

the modern value (250 25 14C yr), while the remaining values are lower. The modern value was calculated by measuring the

14C content of live-collected, pre-bomb marine mollusk shells. This value is in accordance with an active upwelling of strong

intensity that currently occurs off of Portugal. Some primary observations based on data presented here can be made: i) during

the Holocene important changes have occurred in the ocean reservoir effect off the Portuguese coast; ii) these fluctuations

may be correlated with regional oceanographic changes, namely with changes in the strength of coastal upwelling; and iii)

these changes suggest some sort of variability of the climatic factors forcing coastal upwelling off of Portugal.