STABLE ISOTOPIC ANALYSIS AND RADIOCARBON DATING OF MICROPOGONIAS FURNIERI OTOLITHS (SCIAENIDAE) FROM SOUTHEASTERN BRAZILIAN COAST: SEASONAL PALAEOENVIRONMENTAL INSIGHT

Isotopic analysis of Micropogonias furnieri otoliths were used to get insight into palaeoceanographic conditions in the Guanabara Bay and Saquarema Lagoon, Rio de Janeiro state (RJ), located on the southeastern coast of Brazil, under upwelling influence of the Cabo Frio system. Archaeological otoliths come from two Holocene shellmounds (or sambaquis): Galeao and Beirada. For the first time, radiocarbon analysis using high accuracy techniques were performed at Galeao. Age range was determined to be between 5820 and 4980 cal BP, which extends the chronology of human settlement in the Guanabara Bay. Micro-samples of the otoliths were collected sequentially from the core to the edge, to provide continuous delta O-18 and delta C-13 isotopic profiles over the lifetime of the individual fish. Derived-delta O-18(oto) palaeotemperature estimates vary according to seasonality, resulting in a palaeoceanographic variation between 8 to 31 degrees C for Guanabara Bay and 8 and 28 degrees C for the Saquarema Lagoon. Our data indicate that whitemouth croakers were captured during the Middle Holocene from the Guanabara Bay and Saguarema Lagoon and resided in cooler temperatures compared to temperatures of current conditions.

Automated summary

Isotopic analysis of Micropogonias furnieri otoliths provides insight into the palaeoceanographic conditions in Guanabara Bay and Saquarema Lagoon. Radiocarbon analysis of the otoliths extends the chronology of human settlement in Guanabara Bay, while stable isotope profiles reflect the fish's lifetime ocean temperature variations.