The percent blue band reflectance varies from 0% to 70% and shows several trends. The consistently highest values (15% to 70%) and those with the most variation (55% reflectance range) are between 0 and 30 mcd corresponding to ~0. 9 m.y. (Figs. F7A, F8A, F8B). In most marine sediments, this Quaternary interval shows a strong 100-k.y. Milankovitch cycle. Although the possibility of such a cycle is visible in this record, it does not stand out. This may be caused by problems with the age model. Carbonate values in this interval range from ~10% to 75% and with the exception of the interval between 2 and 5 mcd, parallel the blue spectral reflectance values.
Between 2 and 5 mcd percent blue reflectance and percent CaCO3 are out of phase. This could be due to a very wet core, but this is not likely as water content values for this interval measured for Holes 1090A and 1090B are similar to water content values in the rest of the core (Figs. F4, F5; Tables T2, T3). By contract, the percent carbonate values do show roughly the same trend as the GRA bulk density values (Fig. F4B). Alternatively, because water content and spectral reflectance were measured on samples from Hole 1090A, and the carbonate measurements were made on samples from Hole 1090D, it is possible that there is a problem with the composite splice. However, this is also not likely because the shipboard carbonate measurements, made on samples from Hole 1090B, are in agreement with the shore-based measurements made on samples from Hole 1090D. Thus, at this time there is no explanation for the discrepancy between carbonate and spectral reflectance between 2 and 5 mcd.
Between ~30 and 65 mcd (~0.9 and 3.8 m.y.), the range of variation in percent blue reflectance decreases (20% to 55%) and the cycles are much shorter (Fig. F8B), probably corresponding to the 40-k.y. Milankovitch cycle. Each of these cycles is defined by a sharp decrease in percent blue reflectance to close to 20%, with the rest of the cycle being above 40%. Similar cycles identified by a decrease on g/cm3 are also observed in the GRA bulk density measurements (Fig. F4A).
Below ~70 mcd, both the percent blue reflectance values and the GRA bulk density values decrease sharply (Figs. F4A, F7A). This corresponds to the lower Pliocene-lower Miocene hiatus. Percent CaCO3 measurements in this interval are scarce. However, those that are available correlate well with the percent blue reflectance.
In the remaining core, both the percent blue reflectance values and the GRA bulk density values continue to show similar trends, although the detail and magnitude of the changes are different. Below ~160 mcd, when very low percent CaCO3 values (~1%) are encountered, the percent blue reflectance does not indicate as much of a decrease, having values of over 15%. This is in contrast to the very low carbonate values encountered just below the lower Pliocene-lower Miocene hiatus, where percent blue reflectance values were <5%. This is the opposite of the correlation between the low percent carbonate measurements with the GRA bulk density values. The low carbonate correlation is much better in the older sediments (210 mcd) than at the hiatus at 70 mcd (Fig. F4A).