RADIOCARBON RESERVOIR EFFECT VARIABILITY IN CORALLINE ALGAE FROM AMCHITKA, ALEUTIAN ISLANDS

The marine radiocarbon reservoir effect varies both spatially and temporally; therefore, local corrections are vital for any study that relies on radiocarbon dating of marine materials. Currently, much of the Bering Sea along the Aleutian Islands lacks reservoir effect corrections. This study provides new corrections from time-series measurements of radiocarbon in sclerochronologically dated coralline algae (Clathromorphum nereostratum) samples from two locations on Amchitka Island, Alaska, USA. The results yield an average local reservoir effect correction (ΔR) of approximately 400 years at both locations, indicating that this area is relatively radiocarbon depleted compared to the global average marine reservoir. This mean is similar to published values from the Commander Islands near Kamchatka, but over 300 years greater than values measured near the Alaska Peninsula, the only two published ΔR measurements for the region. The 18 measured Amchitka ΔR values varied significantly over time, ranging from 341 years to 513 years between 1883 and 1948. While this short term variability creates greater uncertainty when applying ΔR corrections, it also suggests the possibility of utilizing such data as a paleoclimate proxy. If a consistent relationship between ΔR and related ocean parameters can be established, then older algae may be measured to assess pre-instrumental oceanic conditions. To this end, we will compare the ΔR time series to oceanic conditions measured by regional buoys. These data will be useful to correct mollusk shell radiocarbon dates from Aleutian archaeological sites and sediment cores and provide better insight into the sources and extent of short-term ΔR uncertainty.