Oxygen isotope abundance in quartz from Pacific pelagic sediments

Abstract

Quartz has been isolated from deep-sea cores from the Pacific Ocean. Grain sizes range up to 40 μm, the mode in the distribution being around 5–10 μm. Oxygen isotope ratios in each core sample vary systematically from +16 to +19‰ (relative to SMOW) from coarsest to finest quartz fractions of the North Pacific cores. For a given grain size the isotopic composition is remarkably uniform from core to core. The isotopic abundances are incompatible with either a volcanic or an authigenic origin. The fact that the size distribution and isotopic composition of quartz from the north-central Pacific Ocean are identical with those quartz from surface soils in the Hawaiian Islands suggests that both are derived from the northern hemisphere continents by eolian transport. This conclusion is supported by measurements on quartz from tropospheric dusts collected in Japan and the Caribbean. Quartz isolated from South Pacific cores is consistently lower in 18O than that isolated from the North Pacific but coincides in composition with quartz in eolian deposits in Australia and New Zealand, consistent with aerial transport. The unusual isotopic composition of the quartz may indicate a reservoir of quartz in the arid areas of continents, consisting of quartz derived from igneous and metamorphic rocks mixed with that of low-temperature origin, such as chert.