A Geochemical Study on the Distribution of Some Minor Elements in Deposits and Water Samples of the Antarctic Oases No. 1. The Ra Content of DVDP 13 Core and the Deposits of the Vestfold Hills

Abstract

The ignition loss and the Ra content in the 10% HClO_4-soluble fraction and Na_2CO_3-fusion fraction were respectively determined for the 17 core samples (DVDP 13 core), down to the depth of 50 meters and for the four lake deposits in the Vestfold Hills. The determination of Ra was performed by measuring the activity of Ra in radioactive equilibrium state with a liquid scintillation counter. The detection limit of Ra with 2 grams of sample wag (0.25±0.04)×10^ Ci/g, taking one-eighth of the BG counting rate, 45 cpm, as the limit in this case. Based on the differences between U and Th in geochemical behaviors, it is thought that U is transported into sea water and decays to ^Th which tends to precipitate in the site. From ^Th is produced ^Ra which attains the radioactive equilibrium within a little under ten thousand years. And then, the ^Ra content gradually increases with a half life of 7.5×10^4 years. Therefore, by determining the ratio of Ra in the HClO_4-soluble fraction to that in the Na_2CO_3-fusion fraction of a sample, it is possible to determine its age since the time of sedimentation. The results obtained indicate that the Dry Valley sediment is the oldest while the Lake Stinear sediment is the latest because the ratio is the largest for the former and the smallest for the latter.