A comparison of radiocarbon ages derived from bulk peat and selected plant macrofossils in basal peat cores from circum-arctic peatlands

Databases of basal radiocarbon (14C) ages from peatlands have been used extensively at regional and global scales to examine peatland initiation, land-cover change and carbon cycle dynamics. Many dates collected and analyzed before the 1990s are from bulk peat samples of organic-rich sediments, and such basal radiocarbon ages might have been either too young or too old due to inclusion of non-contemporary carbon via translocation from higher horizons. However, there is rarely a systematic assessment of this problem, especially for large datasets. Here we used AMS 14C dating of both bulk peat and individual macrofossils from the same basal horizon at each of 40 peatland cores across North America and Siberia to evaluate the differences between the two sample types. Our results show that there is no significant or systematic difference between ages derived from bulk material and plant macrofossils. We find that the greatest age overlap of 2σ calibrated age distributions occurred between bulk peat and aboveground macrofossils such as moss fragments, seeds, and herbaceous leaves, suggesting that the bulk material is contemporaneous with the aboveground biomass and active carbon uptake. Dates including wood fragments showed wider divergence compared to moss fragments, seeds, and leaves. We find no evidence for statistically significant and consistent bias introduced by 14C dating of bulk basal peat.