Organic Carbon Aging as Recorded in Marine Sediments from the Cabo Frio Upwelling System (South-Eastern Brazil)

Summary The ¹⁴C-age offset between the organic matter (OM) and carbonates buried in marine sediments of the Cabo Frio upwelling system during the past 6.5 kyr was investigated. The ¹⁴C-ages of the OM were 787 ± 166 years older than those of foraminifera, which might be indicative of a long-term storage and re-processing of the OM on the mid-shelf sediments caused by local upwelling-related hydrodynamic processes. A gradual increase up to the maximum ¹⁴C-offset from 5.8 to 4.0 cal kyr BP may be a response to the intensification of the Brazil Current activity over the shelf, extending the sediment translocation and, consequently, the OC aging. Also, an intensification of the South American monsoon during this period might had favored the input of pre-aged terrigenous OM. Between 4.0 and 2.0 cal kyr BP the ¹⁴C-offset decreases, possibly due to a subsequent weakening in the bottom currents. After 1.8 cal kyr BP, a slightly increase in the ¹⁴C-offset could be caused by an upwelling enhancement. These results reinforce the existence of a temporal decoupling between the organic proxies commonly used in paleoceanographic studies and the correspondent age models applied, which highlights the need to interpret proxy-based information with caution, especially in upwelling regions.