Stratospheric Carbon-14, Carbon Dioxide, and Tritium

U. S. Geological Survey Radiocarbon Dates V

The dates listed herein have been determined at the U. S. Geological Survey radiocarbon laboratory at Washington since our last date list (USGS IV) and up to the end of 1959. Acetylene continues to be the gas of our choice. Each sample is run for a period of two days in two separate counters with separate electronics. The modern standard used is wood grown in the 19th century, and the ages and errors have been computed in the same manner as before. Pretreatment of wood, charcoal, and peat samples by boiling in acid, alkali, and acid again, is standard procedure.

Meteorological benefits from atmospheric nuclear tests

The presence in the atmosphere of radioactive debris from nuclear tests provided a unique opportunity to study atmospheric motions and transfers of trace substances. Measurements of the concentrations in air of radionuclides were used to verify trajectories derived solely from weather data. The profiles of radioactive concentration along the aircraft tracks were non-Gaussian. High-flying aircraft and balloons collected air and particulate samples to approximately 30,000 m from Alaska to South America. The measurements from these samples were used in verifying stratospheric motions on a hemispheric and global scale. Other benefits to the atmospheric sciences gained during the nuclear testing era are briefly described.

Volcanic dust in the atmosphere; with a chronology and assessment of its meteorological significance

After defining the terms commonly used in reporting volcanic eruptions and noting previous approaches to assessment of their magnitudes, this study proceeds to examine aspects of importance, or possible importance, to meteorology―principally the dust veils created in the atmosphere, particle sizes and distribution, heights, fall speeds and atmospheric residence times. Later sections deal with spread of the dust by the atmospheric circulation and the direct effects apparent upon radiation, surface temperature and extent of ice in the polar regions. These effects, as well as various crude measures of the total quantity of solid matter thrown up, are used to arrive at numerical assessments of volcanic eruptions in terms of a dust veil index (d. v. i.). The latitude of origin of the dust (latitude of the volcano) receives some attention, and apparently affects the course of development of the atmospheric circulation over the three or four years following, at least in the case of great eruptions (d. v. i. > 100 over one hemisphere). Effects upon the extent of ice on the polar seas may be of somewhat longer duration, and thereby influence the atmospheric circulation over a longer period of years, since there seems to be some association with the cumulative d.v.i. values when successive great eruptions occur with only few years between. The time distribution of volcanic dust since the last Ice Age, and since a. d. 1500, are indicated in as much detail as the evidence permits. Some associations with changes of climate are suggested, but it is clear that volcanic dust is not the only, and probably not the main, influence in this. The appendices give a chronology of eruptions (including those which it seems possible to dismiss as regards any effect on world weather or climate) and a chronology of d. v. i. values. A third appendix displays by means of graphs the variation of some circulation parameters in January and July in the region of northwest Europe over the years immediately following forty of the greatest eruptions since 1680.

Latitudinal Effect in the Transfer of Radiocarbon from Stratosphere to Troposphere

Latitudinal variations in the descent of bomb-produced radiocarbon from the stratosphere is suggested by differences in tropospheric carbon-14 activity. The magnitude of a similar latitudinal effect in the pre-bomb steady state is estimated. This effect may be part of the explanation of the short-term oscillations in carbon-14 activity found in treerings from the last 1300 years.

Post-Bomb Rise in Radiocarbon Activity in Denmark

During the summers of 1958 and 1959 the increase in concentration of bomb-produced radiocarbon in Denmark was several percent higher than the average increase for the hemisphere. This additional increase is probably a carbon-14 equivalent to the spring peaks in strontium-90 fallout in the North Temperate Zone in the same years, and suggests latitudinal variations in carbon-14 contamination.