Figure F33. A. Quartz distribution in surface sediments of the subtropical southeast Pacific, expressed as weight percentage (carbonate- and opal-free basis, reproduced from Molina-Cruz, 1977). Arrows indicate trade winds. Sites 1236, 1237, 1238, and 1239 are shown with their plate tectonic backtracks. B. Siliciclastic accumulation rates and hematite peak height at Sites 1236 and 1237. The accumulation rates of siliciclastics were estimated as (100% - wt% CaCO3 - wt% organic matter - wt% biogenic opal) x sedimentation rate x dry bulk density. The shipboard magnetostratigraphy and biostratigraphy were used to calculate sedimentation rates that were smoothed to avoid overinterpretations of the preliminary age model. Siliciclastic accumulation rates at Site 1237 are used as a proxy for dust flux. The hematite peak height is derived from color reflectance spectra and serves as a proxy for changing concentrations of hematite. MAR = mass accumulation rate.