AMS C-14 CHRONOLOGIES OF HOLOCENE LAKE-SEDIMENTS IN THE ABISKO AREA, NORTHERN SWEDEN - A COMPARISON BETWEEN DATED BULK SEDIMENT AND MACROFOSSIL SAMPLES

AMS-radiocarbon dates of bulk sediment samples were compared to AMS-ra diocarbon dates of terrestrial plant macrofossils from two neighbourin g lakes in northern Sweden. Both sediment successions cover the period from the last deglaciation to the present. The sediments in Lake Tibe tanus are highly calcareous, whereas the laminated sediments in Lake V uolep Njakajaure are composed mainly of algal gyttja with a low carbon ate carbon content. The ages of the radiocarbon dated terrestrial macr ofossils are in close agreement with the lamina chronology in Lake Vuo lep Njakajaure. All bulk sediment samples give older radiocarbon ages than radiocarbon ages obtained from terrestrial macrofossils. The magn itude of the radiocarbon age error in Lake Tibetanus is not constant t hroughout the profile but ranges from c. 550 to 2700 years. The error is less pronounced in Lake Vuolep Njakajaure and ranges from c. 250 to 800 years. Determination of the deglaciation age in this region of no rthern Swedish Lappland generally relies on bulk sediment dates, which are likely to be erroneous. Radiocarbon chronology of lake sediments must be based on radiocarbon dates of terrestrial macrofossils.