This list includes some significant measurements carried out by CRAD Radiocarbon Laboratory from 1979 to 1985. The dates were obtained by liquid scintillation counting of benzene using the laboratory procedures described in previous lists (Barbina et al 1982: 214-216; Barbina, Calligaris & Ciuti 1979). Samples were pretreated according to generally applied methods, depending on type of material and particular archaeologic and geologic features.

In terms of both quenching and, in particular, counting efficiency, scintillation counters employing burst counting circuitry are sensitive to changes in scintillant concentration. Our research demonstrates that there are plateau regions where neither parameter is significantly influenced by moderate changes in a cocktail containing butyl PBD and bis MSB. One of these, consisting of butyl PBD 2.8mg.g-1 and bis MSB 3mg.g-1 of benzene is recommended for these counters, as it enables open window counting efficiencies of ca 90% while exhibiting optimal resistance to quenching. A method for accurate dispensing of such small weights is also described.

Radiocarbon was measured in dissolved inorganic carbon (DIC) and living organisms collected off the west coast of Baja California in October 1980. Samples from three locations were examined. Delta-14C of DIC at the southernmost station was higher than those further north, which reflects reduced upwelling in the southern region. Crabs and anchovies had Delta-14C values significantly lower than surface DIC Delta-14C, indicating the incorporation of ‘older', sediment-derived carbon sources from their diets. Comparisons are made between our DIC Delta-14C measurements and those obtained during other cruises and at a coastal site, from 1959 through 1987. Two distinct time histories of DIC Delta-14C are apparent for the post-bomb period: 1) a lower Delta-14C curve for sites close to the coast influenced by enhanced coastal upwelling; and 2) a higher Delta-14C curve for sites further offshore within the California Current.