Pedogenic Element Distribution in Soils from Guana Island, British Virgin Islands.

Weathering-related changes in element distributions provide a reliable means for assessing soil development. We applied this technique to four soil profiles across Guana Island, British Virgin Islands (BVI), which has a mean annual precipitation of 840 mm and a peak elevation of 246 m. The island formed from late cretaceous deposits as well as and dating more than 70 million years. Soils were formed mainly from andesite flows and tuff parent material, as well as conglomerate from uplifted, late cretaceous deposits. All soils were collected from level surfaces along the spine of the island. We assessed elemental loss and gain during soil profile development using an open-chemical-system transport function (τ, or tau), normalized to the index element Nb. We determined the total carbon (C) of the samples by dry combustion. In the surface soils we found substantial losses of Fe, Al, and Si (tau values -0.95 to -0.4), but below 30 cm values approached those of the parent rock. For alkaline bases (Ca, Mg, and Na) the tau values were negative in the soil profile with higher loss of these elements in the surface soils (τ > -0.5) than the subsoils (between -0.4 and -0.2). An exponential reduction of total carbon was observed down soil profile, varying from 5.1 ± 1.5 % to 0.6 ± 0.2 % of C in the 0-5 cm and 45-60 cm, respectively, of the mineral soil. We will also present data on rare earth element distributions to establish potential patterns of dust on elemental distributions. Since the Island’s climate is semiarid, results from this study will be important to better understand the biogeochemistry of Caribbean islands.