Systematic analyses of radiocarbon ages of coexisting planktonic foraminifera

ABSTRACT We compare radiocarbon ( 14 C) ages of coexisting planktonic foraminifera species from sediment cores VM12-107 and KNR166-2-26JPC from the Equatorial Atlantic Ocean for three time periods (Holocene, Heinrich Stadial 1, last glacial maximum). We find a maximum inter-species difference of 1200 14 C yr. On average, the 14 C ages deviate by ∼300 yr between Globigerinoides ruber and other species. In most cases, this exceeds the analytical uncertainty range of the measurements and thus renders the choice of species for generating age models as important as sample weight. While modern stratified water-column profiles imply an increase in 14 C ages with water depth, we observe an expected parallel increase of 14 C ages and δ 18 O only at VM12-107. The mismatch between 14 C ages and δ 18 O at KNR166-2-26JPC likely results from the effects of bioturbation and the hydrographic setting. The largest difference in 14 C ages between mixed-layer versus thermocline-calcifying planktonic foraminifera are observed during Heinrich Stadial 1 despite a decrease in upper-ocean stratification at that time. This difference is likely the result of inconsistent increases in 14 C reservoir ages during times of reduced overturning circulation masking the potential of 14 C ages of coexisting planktonic foraminifera to reflect the density stratification of the water column.