Distribution of fluorine in recent marine sediments related to petrographic composition: Bransfield Strait and northwestern Weddell Sea, Antarctica

The fluorine budget of 40 marine surface sediment samples from the Atlantic sector of the Antarctic seas has been examined in order to elucidate the relationship between granulometry, mineralogy, major and minor element chemistry, and the fluorine distribution. The concentrations of total fluorine range from 243 to 800 ppm ( x ̄ = 423 ppm). The clay and fine-silt fractions contribute 60-87% to the total concentration of fluorine. The clay fraction consists of clay minerals, detrital quartz, feldspars and an amorphous component (biogenic opal and volcanic glass shards). The fluorine concentrations in the crystalline components of Bransfield Strait and Weddell Sea sediments are 551-557 and 724-825 ppm, respectively. These variations are almost exclusively due to varying proportions of illite, which is enriched in fluorine to a considerable extent. Montmorillonite and mixed-layer clays, which carry approximately as much fluorine as illite, are present in insignificant amounts and are therefore of minor importance in the total fluorine concentration in these sediments. Biogenic opal (essentially diatom skeletons), which accounts for 3-77 wt.% of the clay fraction, contains 15 ppm fluorine. Thus, fluorine abundance in the clay fraction is negatively correlated with the content of biogenic opal. Volcanic glass shards contain 1688-3758 ppm fluorine. They comprise only up to 3 wt.% of the clay fraction and are therefore of minor relevance in the total fluorine budget in these sediments.