The variable nature of the coastal 14C marine reservoir effect: A temporal perspective for Rio de Janeiro

The radiocarbon (C-14) marine reservoir effect (MRE) is very sensitive to physical and chemical processes affecting the local carbon (C) cycle. In coastal zones, these tend to be numerous and complex, hindering the derivation of local marine reservoir offsets (Delta R) for the establishment of archaeological chronologies. Although discussions of how the magnitude of the MRE responds to factors such as the presence of coastal upwelling are common in the literature, little has been done to assess how the effect is influenced by a changing relative sea level. Here, we address the MRE temporal variation on the coast of Rio de Janeiro in the light of updated C-14 calibration curves and considering the Holocene relative sea-level curve for the region. To achieve this, we employ Bayesian modelling to analyze published and new C-14 ages from Brazilian archaeological sites and prebomb samples. In this study, we show evidence for a Late Holocene increase in the MRE, varying from -577 +/- 56 C-14 yr at ca. 5500 cal BP to -29 +/- 25 C-14 yr at present, associated with a decreased relative sea-level.

Automated summary

This study uses Bayesian modeling to analyze C-14 age data from Brazilian archaeological sites and prebomb samples, and finds evidence of an increasing marine reservoir effect (MRE) during the Late Holocene, ranging from -577 +/- 56 C-14 yr at ca. 5500 cal BP to -29 +/- 25 C-14 yr at present, associated with a decreasing relative sea level.