RARE EARTH ELEMENT ANALYSIS OF SOIL WEATHERING PROFILES IN VARYING CLIMATE ZONES ON THE ISLAND OF HAWAI’I

Rare earth elements (REEs) are usually considered to be immobile elements but are variably mobile during weathering of silicate rocks. Phosphate minerals are an important source of P and REEs. So, REE behavior reveals information about nutrient (P) behavior during pedogenesis. The goal of this study is to observe how REE concentrations change in soil samples with varying depth and climate. In this study, I present REE data for soil weathering profiles sampled from two locations on the Kohala Peninsula in Hawai’i. Multiple samples were collected from a wet and dry climate at varying depths. At the low-rainfall end of the Kohala climate gradient, the near-surface soils are enriched in REEs relative to the parent rock. This is likely attributed to the leaching of more soluble major elements during pedogenesis. Deeper in the soil column, REE concentrations are closer to the parent rock as they have not experienced heavy weathering. These soils have significant concentrations of phosphorus (>180,000 ppb). At the high-rainfall end of the Kohala climate gradient, there is no phosphorus in the soil which may be a result of uplift and erosion of phosphate materials with the more frequent rain. In the near-surface soils, LREE (light REE) enrichment is probably caused by the transport of Asian dust to the islands of Hawai’i. Deeper in the profile, LREE and MREE are depleted since LREE and MREE weather out along with phyllosilicates. The differences between the weathering profiles imply the climate is the main contributor of the variable REE concentrations.