THE MARINE RESERVOIR EFFECT ON THE COAST OF RIO DE JANEIRO: DERIVING ΔR VALUES FROM FISH OTOLITHS AND MOLLUSK SHELLS

Considering the impact of coastal dynamics on the radiocarbon (C-14) marine reservoir effect (MRE), upwelling has the potential of enhancing marine influence, usually C-14 depleted. Freshwater input can contribute either to increased reservoir offsets, when dead carbon from rock weathering is available, but also towards an atmospheric C-14 signal, when the presence of terrestrial organic matter from catchment prevails. An overview of the MRE studies based on shellmounds on the coast of Rio de Janeiro reveals a pattern of negative local corrections for Saquarema and Rio das Ostras but positive values for Cabo Frio island, suggesting the presence of cold upwelling waters in Cabo Frio at 1.6-1.2 cal kBP. New results for a shellmound on the Ilha Grande island, in the western portion of the Rio de Janeiro coast, revealed a negative value at about 3 ka. We discuss distribution of MRE values and temporal variability in the region and their relation to ocean dynamics, continental input and the choice of marine organisms used for R determination. A comparison of local reservoir offsets for the Saquarema region obtained from fish otolith and mollusk shells revealed similar R distributions, showing that both materials can be equally used.