REVIEW OF RADIOCARBON DATING IN ANTARCTIC MARINE SEDIMENTS

Radiocarbon dating in Antarctic marine sediments is associated with several problems unique to the Southern Ocean but its careful application over the last ten years has contributed greatly to the development of near-continuous time series for late Quaternary paleoclimate research. Problems that need careful consideration when applying the method include: corrections for marine reservoir variation, vital effects between different marine species, seasonal differences in marine phytoplankton 14C activity and resuspension of organic particulates. Reservoir corrections for modern calcareous species range over 600 years for modern living organisms. Vital effects may explain some variability but differing regional reservoirs and post-bomb mixing of deep waters are also involved. This variation is equal to estimates for changes in reservoir correction during the Holocene as based upon independent radioisotope methods. Such corrections may be premature until we understand the regional variation in 14C activity in living marine carbonates. Reworking of organic matter is a pervasive problem amplified by: strongly pulsed seasonal flux of organics, resuspension induced by icebergs and deep infaunal mixing, bottom currents, and the presence of deep shelf basins which serve as repositories for resuspended marine detritus. Use of particulate organic matter for radiocarbon dating is generally discouraged but in many instances such material provides the only 14C carrier within the sediment. In such cases standard corrections based upon the surface age of organic particulates are routinely applied but the results do not always produce an accurate chronology for sediment horizons deeper in the stratigraphy. Yet, the method has produced reliable chronologies where the input of reworked organic matter is strictly limited by either basin geometry and/or limited sedimentary source terrain (Palmer Deep). In cases where these conditions are not met separation of organic matter into compound classes, such as sterols, can produce more reliable ages (a method pioneered by the NOSAMS). Important sequences do not always contain sufficient sterol abundance for widespread application of this method. New guidelines for radiocarbon dating in Antarctic marine sediments are provided for the benefit of the community.