SYSTEMATIC ANALYSES OF RADIOCARBON AGES OF COEXISTING PLANKTONIC FORAMINIFERA

Abstract

ABSTRACTWe compare radiocarbon (14C) 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 120014C yr. On average, the14C ages deviate by ∼300 yr betweenGlobigerinoides ruberand 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 in14C ages with water depth, we observe an expected parallel increase of14C ages and δ18O only at VM12-107. The mismatch between14C ages and δ18O at KNR166-2-26JPC likely results from the effects of bioturbation and the hydrographic setting. The largest difference in14C 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 in14C reservoir ages during times of reduced overturning circulation masking the potential of14C ages of coexisting planktonic foraminifera to reflect the density stratification of the water column.