Antarctic snow chronology with Pb²¹⁰

Abstract

After a short discussion on the Pb210 dating method, the results of Pb210 measurements on snow and firn samples from four Antarctic stations are reported as well as the experimental procedure used. Pb210 was also measured in the air at ground level, at Base Roi Baudouin, the average Pb210 activity of aerosols in 1958 being 1.3 × 10−3 dpm/kg of air. In samples of surface snow accumulated during the last two to five years, the average Pb210 activity is of the order of 100 dph/kg of snow. This activity seems to be independent of the local rate of accumulation. The variations of Pb210 activity as a function of depth were studied on two vertical firn profiles spanning an interval of more than 200 years, at Base Roi Baudouin (70°S, 24°E) and at Amundsen Scott Station (South Pole). Within experimental errors, the Pb210 activity was found to decrease exponentially with depth at both stations. The most plausible interpretation is that the rate of water accumulation and the initial Pb210 concentration in the snow have remained constant at both places over the last 100 years. The annual rates of water accumulation calculated from the decay curves are 6±1 cm at the South Pole and 45±3 cm at Base Roi Baudouin, in good agreement (to better than 10 percent) with accumulation rates so far obtained by other methods.

Determination of the Rate of Snow Accumulation at the Pole of Relative Inaccessibility, Eastern Antarctica: A Comparison of Glaciological and Isotopic Methods

“…Deviatio ns from this rule have been observed ; nevertheless, the number of d epth-hoar layers is a fair approximation of the number of years. This conclusion is also substantiated by res ul ts obtained by geochemical m ethods (Picciotto and others, 1964 ;Wilgain and others, 1965 ) . Giovin etto's ( 1960) observations show that the annual stratification is still vi sibl e at depths up to 26 m.…”

“…Similar investigations have a lready been conducted at the South P ole, yielding con sistent accumulation-rate values around 7 g cm -2 year-I (Picciotto and others, 1964;Wilgain and others, 1965;Epstein and oth e rs, 1965) in good agreement with the value d erived from stratigraphy studies (Giovinetto, 1960;Gow, 1965 ) and surface measurements.…”

“…Owing to its 22 years half-life, it could be used for dating firn and ice samples back to approximately 100 years (Goldberg, 1963;Crozaz and others, 1964;Crozaz, unpublished) . L et Ao = the " oPb specific activity of the snow at the time of deposition, A h = the 2l 0 Pb specific activity of firn or ice at a depth h, h = the depth from the surface, expressed in g cm-2 or cm of water, a = the annual rate of snow accumulation in g cm-' year-', and ,\ = (0.032 ± 0.001 ) year-" the radioactive constant of2IoPb.…”

A Flow Model and a Time Scale for the Ice Core from Camp Century, Greenland

“…T ritium (Aeger ter a nd o thers, 1969) a nd 2l OPb (Goldberg , 1963;C rozaz and others, 1964 ;C rozaz and Langway, 1966) reach only 100 years back in time . Th e other two, 3 2 Si (Dansgaard and others, 1966) a nd 14 C (Sch olander a nd others, 1962 ), may b e d etected in 3000 a nd 20000-30000 year-old ice, resp ectively, but both of th ese techniques r equire several tons of ice.…”

Fine-grained sedimentation on the Chenier Plain Coast and inner continental shelf, northern Gulf of Mexico

“…SIn (2) (4.2) Accumulation rates obtained using this standard CFCS method were compared with accumulation rates obtained by a second method, which uses a Constant Rate of Supply model (Crozaz et al, 1964;Appleby and Oldfield, 1978 Pb is supplied at a constant rate to sediment through time, but that the initial 210 Pb concentration in the sediment, and the supply rate of sediment to the particular site investigated, may vary (e.g., Crozaz et al, 1964;Appleby and Oldfield, 1978;Noller, 2000). This model allows determination of the age of sediment at a given depth in the core, using integrated 210 Pb activity below the depth considered.…”