Radiocarbon and 210Pb distribution in submersible taken deep-sea cores from project FAMOUS

During the FAMOUS survey of the Mid-Atlantic Ridge in August and September, 1974 by the research submersible 'Alvin' two cores were taken for radiochemical analysis. One core (527-3) was 24 cm long and the other (530-4) was 17 cm long. Both were from water depths of about 2500 m. Slices of the cores were analyzed for radiocarbon and 210Pb. In the top 8 cm layer of 527-3 dates are constant with depth at about 2400 yr B.P. Below 8 cm radiocarbon dates increase linearly yielding an accumulation rate of 2.9 cm/103 yr. The constant age from the surface to a depth of 8 cm can be attributed to biogenic mixing to that depth with no significant mixing below 8 cm. The excess 210Pb pattern yields a mixing coefficient of 0.6 X 10-8 cm2/sec. The top 2 cm of core 530-4 has a 14C date of 13,000 yr B.P. Below 4 cm dates increase from 16,400 to 18,000 yr B.P., but this increase probably is not statistically significant. The data indicate physical disruption of the section. The date of this disruption is not defined by the data but the restriction of excess 210Pb to the top centimeter of the core implies either that sediment accumulation at this site has only recently resumed or that both the rate of accumulation and rate and depth of bioturbation have been very small since the disrupting event. (Auth.)