AMS 14C dates were measured for 28 mollusk shells collected live in Danish waters over the period AD 1885 to 1945. Fourteen samples were from fjords and 14 were marine samples from the Danish Skagerrak-Kattegat coastal area and from the Belts. Reservoir ages were calculated for all samples on the basis of the tree-ring calibration curve. For the marine samples, which cover the period AD 1885-1916, we found a weighted-average reservoir age of 377 +/16 yr. The marine Delta-R values (the difference between the measured 14C age and the age deduced from marine, mixed-layer model calculation of Stuiver, Pearson and Braziunas (1986)) were found to be uniform within the experimental uncertainty with a weighted average of Delta-R = 13 +/16yr. Based on the observed scatter, the standard deviation is 21 yr. This result shows that it is justified to use the marine calibration curve with standard parameters (Delta-R = 0) when 14C-dating marine samples from the Danish area. Our value is consistent with the result Delta-R = -33 +/27 yr previously found for the Norwegian and Swedish Skagerrak-Kattegat coasts. In contrast, reservoir ages for Danish fjords were found to vary from 400 to >900 yr, far beyond experimental uncertainty. We ascribe this to varying content of dissolved, old soil carbonate (hard-water effect). Therefore, dating of samples from such fjord environments is expected to be uncertain by several hundred years.

Radiocarbon was measured in atmospheric CO2 from La Jolla, California and in living organic materials from six sites in the northern hemisphere. Atmospheric CO2 Delta-14C values from La Jolla agreed with those previously published records from China Lake, California (Berger et al.1987) and Vermunt, Austria (Levin et al.1985). Delta-14C values of fruit and grain samples that grew during 1980 agreed with the atmospheric CO2 Delta-14Cmeasurements. Most of the Delta-14C results of fruit and corn samples stored since the 1940s agreed with tree-ring Delta-14C values for the same time period. In general, agreement was found between the atmospheric CO2 or tree-ring Delta-14C records available for the Northern Hemisphere and the Delta-14C signatures of rapidly exchanging organic matter pools examined in this study. Exceptions were the Delta-14C values of carbonate from egg shells and that of organic carbon from egg insides, which demonstrate that bicarbonate and organic carbon within the egg follow different biochemical pathways.

An important recent development in the field of geomorphology has been the application of in-situ cosmic-ray-produced nuclides to obtain model erosion rates and surface exposure ages. These concepts emerged some four decades ago in studies of cosmogenic nuclides in meteorites, but cannot generally be used analogously for terrestrial rocks. The differences in the two cases are outlined. For the case of steady-state erosional histories, the terrestrial surface exposure ages depend on the half-life of the radionuclide studied. A suggestion is made for presenting the surface exposure ages, which allows a clear definition of the meaning of the estimated exposure ages. In the case of a discrete exposure history, the meaning of "exposure age"—which should more appropriately be called "event age"—is however quite unambiguous.

In 373 BC a catastrophic earthquake and seismic sea wave destroyed Helike, a Greek city near Aigion on the southern shore of the Gulf of Corinth. The ruins were buried by sediments of unknown depth, leaving no trace of the city. We here discuss the radiocarbon dating of organic sediment samples recovered from seven boreholes drilled on the coastal plain in the area where ancient sources located Helike. Most of the samples apparently acquired a substantial addition of older carbon from natural sources, and hence their apparent ages are older than the true ages of sedimentation. However, if we assume that the addition is systematic, we can use the apparent ages to show that the sedimentation rate was initially rapid (about 1 cm yr-1) for the strata between 40 and 10 m below the surface, and then decreased by an order of magnitude about 6500 yr ago. A related change in the sediment deposition at about the same time has been found in many other marine deltas throughout the world, probably due to the deceleration of the global sea-level rise. We conclude that in the boreholes sampled by the present data, the horizon corresponding to ancient Helike is less than 8 m deep.