RADIOCARBON CONTENT OF PRE-BOMB MARINE MOLLUSKS AND VARIATIONS IN THEC-14 RESERVOIR AGE FOR COASTAL AREAS OF THE BARENTS AND KARA SEAS, RUSSIA

Fourteen mollusks, collected alive between 1900 and 1945 from the Russ ian Parents and Kara seas, were analyzed by AMS C-14 dating to evaluat e variations in the C-14 marine reservoir for arctic coastal sites, wh ich is important for correcting ages in paleoenvironmental time-series and advancing understanding of the exchange of carbon. The C-14 ages on the mollusks reveal a range of marine reservoir values (R(t)) from 159 C-14 yr to 764 C-14 yr. The oldest R(t) values of 764 to 620 C-14 yr are for the bivalve Portlandia arctica, which often inhabit cold an d low salinity waters and muddy substrates. The depleted C-14 content for this bivalve reflects possibly the incorporation of old carbon fro m freshwater inputs and/or the consumption of old organic matter from the underlying sediments and pore waters. Other mollusks with sessile habitats and pelagic food sources gave significantly lower R(t) values between 159 and 344 C-14 yr. The youngest R(t) values indicate enrich ment in C-14 and may partially reflect enhanced transfer of C-14-enric hed CO2 from the atmosphere to the ocean surface with wind-generated w ave agitation. This study underscores that a variety of processes can lead to variable C-14 depletion and enrichment of surface waters yield ing a ca. 600 year age span for contemporaneous arctic mollusks. There may be added uncertainty in the C-14 reservoir correction for deposit -feeder species such as Portlandia sp. and perhaps for certain benthic foraminifera (e.g. Nonion labradoricum) because these taxa often inco rporate old organic matter from the substrate. A reservoir correction of greater than or equal to 700 years may be more appropriate for infa unal, deposit-eater species, particularly in glacier-dominated environ ments. Mollusks and foraminifera with sessile habits and pelagic food sources should be selected preferentially for C-14 dating, because the ir shells may more closely reflect the C-14 content of the global-ocea n mixed layer.