PRE-BOMB RADIOCARBON AND THE RESERVOIR CORRECTION FOR CALCAREOUS MARINE SPECIES IN THE SOUTHERN-OCEAN

Four Antarctic marine mollusc shells, which were collected alive betwe en 1917 and 1940, were analyzed by accelerator mass spectrometry to pr ovide the first pre-bomb radiocarbon measurements of biogenic carbonat es from the Southern Ocean. After correcting for the impact of fossil fuel combustion (Suess Effect) radiocarbon activities of the pre-bomb shells averaged -149.8 +/- 10.4 parts per thousand In contrast, the De lta(14)C values for post-bomb molluscs, echinoderms, brachiopods and f oraminifera averaged -96.1 +/- 25.2 parts per thousand These biogenic carbonate Delta(14)C values are nearly identical to pre-bomb estimates (-148 parts per thousand to -152 parts per thousand) and post-bomb me asurements (-98.4 +/- 22.0 parts per thousand) of the surface waters i n the Southern Ocean. Average radiocarbon ages of the biogenic carbona tes before and after 1950 (1303 +/- 84 years and 811 +/- 205 years, re spectively), along with those from seals and penguins, indicate that t he Antarctic marine radiocarbon reservoir has decreased in age by near ly 500 years during the second half of the 20th century. Marine specie s and seawater measurements firmly place the radiocarbon reservoir cor rection at 1300 +/- 100 years for calcareous marine fossils which are widespread, abundant and well-preserved organic materials for interpre ting ice-sheet, climate and sea level impacts on the Antarctic marine ecosystem during the Holocene.