Diffuse spectral reflectance measurements were made with the Oregon State University split-core analysis track (SCAT). This instrument or its prototype has been used to measure reflectance sediments during Leg 138 (Mix et al., 1992, 1995), Leg 154 (Harris et al., 1997; Harris and Mix, 1999), and Leg 162 (Ortiz et al., 1999) sediments. The instrument measures light reflected from split sediment core surfaces at a spectral resolution of 0.68 nm and spans wavelengths from 250 to 950 nm, thereby including the upper ultraviolet (UV), visible, and near-infrared wavelengths. The core is illuminated via a fiber-optic cable by two light sources, a deuterium lamp for the UV and a quartz-tungsten-halogen lamp for the visible and near-infrared (nIr) wavelengths.
During Leg 177, closely spaced measurements were converted to percent reflectance and averaged into four 100-nm-wide bands defined as (1) UV (250-350 nm), (2) blue (450-550 nm), (3) red (650-750 nm), and (4) nIr (850-950 nm) (Table T4). The signal is most reproducible in the red and blue wavelengths. Although values for these two wavelengths have similar trends, they do show variations attributed to different components of the sediment (Fig. F6). The blue band is used for comparison to the CaCO3 content of sediments because calcite has a somewhat higher reflectance at this wavelength than at longer wavelengths. Because of this, percent blue reflectance should be a better proxy for CaCO3 (see Mix et al., 1995) (Figs. F7, F8).