Six sediment cores were obtained from the Cabo Frio shelf region of coastal Brazil to quantify the accumulation of organic carbon in a highly productive upwelling region. The sampled locations, 10–60 km offshore at∼100 m water depth, were investigated for excess 210Pb (210Pbex) as well as 239+240Pu fallout activities to determine sedimentary dynamics. The 210Pbex and 239+240Pu dating models show that the sediment accumulation rates varied substantially throughout this complex hydrodynamic system (0.8 to 5.5 mm yr−1). Excess 210Pb and 239+240Pu fluxes indicate lateral transport, with varying intensity along the continental shelf. The stations with the greatest 210Pbex and 239+240Pu sediment inventories are also the sites with the highest carbon accumulation rates (CAR). The total organic carbon (TOC) and total nitrogen (TN) contents, along with the δ13C results, indicate that the organic matter deposited in this region is mainly of marine origin. The results of this work suggest that lateral transport, with varying intensity along the shelf, contribute to the large quantities of marine plankton buried at specific depositional settings in the Cabo Frio upwelling region (∼ 1 to 8 mol of OC cm−2 yr−1).