23. REGIONAL AND STRATIGRAPHIC PATTERNS IN COLOR REFLECTANCE OF SEDIMENTS FROM LEG 175 1

During Leg 175, color reflectance was routinely measured downcore at all sites (1075–1087). These measurements allow determination of the light reflectance from the sediment surface in the visible wavelength band (see “Explanatory Notes” chapter, this volume). Previous studies have shown that the ratio between reflectance values of the red and blue wavelengths is closely related to diagenetic redox conditions in the sediment, reflected in the presence of iron oxyhydroxides or sulfides (Mix et al., 1992; Schneider et al., 1995). Reflectance data can be a suitable proxy for reconstructing high-resolution changes in carbonate sedimentation (see Curry, Shackleton, Richter, et al., 1994). Leg 175 drilled a north–south transect along the southwest African margin (5°S to 31°S, 10°E). The sediments consist of different lithologies, ranging from carbonate-poor sediments with varying amounts of biosiliceous and terrigeneous material in the north to carbonate-rich sediments at the southernmost sites (see Wefer et al., Chap. 16, this volume). This chapter briefly summarizes the regional and stratigraphic patterns in color reflectance of sediments recovered during Leg 175. First, we show the relationship between lithology and color reflectance and, second, how stratigraphic changes in the color data can be used to obtain clues to climate forcing in the different sedimentary environments drilled during Leg 175.