Department of Earth System Science

 In the late 1980s, bomb ¹⁴C was present in suspended particulate organic carbon (POC) from the North Central Pacific (NCP) and Sargasso Sea (SS) throughout most of the water column, demonstrating that deep POC had exchanged with atmospheric CO₂ in the past 30 years. Upon reoccupation of these sites in 1999 and 2000, respectively, we observed that the δ¹³C values of suspended POC were lower than those measured a decade earlier. This demonstrates that anthropogenic CO₂ from fossil fuel and biomass burning has penetrated a major organic matter pool in the deep ocean. Δ¹⁴C measured in the suspended POC showed similar or higher values in the deep Sargasso Sea and decreased values in the deep NCP compared to those measured previously. We use a box model to show that the differences in the radiocarbon results are likely due to the presence of resuspended sediment that is laterally advected from the continental margin to the deep Sargasso Sea.