Nineteenth-century expeditions and the radiocarbon marine reservoir effect on the Brazilian coast

Abstract

Several scientific expeditions surveyed the ocean during the 19th century, gathering a wealth of interdisciplinary data as well as samples of different kinds. The latter are currently held by museums worldwide, and are the subject of study in different sciences, offering a unique opportunity to access information which is not readily available elsewhere. This is the case for research involving the offset in 14C (or radiocarbon) activity between the ocean and the atmosphere, termed the Marine Reservoir Effect (MRE), which is responsible for apparent 14C ages in marine material. The quantification of this discrepancy is crucial for the 14C dating tool since corrections must be applied for the accurate calibration of marine 14C ages. Nevertheless, the difficulty of finding suitable material for assessing the MRE contributes to the current scenario of scarce and patchy data. Here we propose the use of samples collected during well-documented 19th-century scientific expeditions in order to overcome the lack of information that prevents the use of many museum specimens in MRE studies. Approximately 60 mollusk shells and a sea urchin, collected from the coast of Brazil, were analysed for their radiocarbon age, δ13C and δ18O. The MRE is variable, with considerably high values occurring at specific spots along the shoreline. The data indicate a rather large area of upwelling influence on the southeastern coast of Brazil and possible dissolution of 14C-free limestone in the northeast. The results shed light on processes affecting the 14C concentration of Brazilian coastal waters, bearing implications for palaeoenvironmental and archaeological studies performed in the region. Moreover, the data generated in this study will be useful for the validation of 14C simulations in numerical models. Finally, this paper offers a discussion of the importance of natural history collections which looks beyond the preservation of our biodiversity.