The bulk carbonate content in both intervals exhibits nearly the same variability, ranging from 93% to 63% and 94% to 68% CaCO3 in lithologic Subunits 1A and 1B, respectively. Primary differences between Subunits 1A and 1B is that the former exhibits a longer cycle length (Fig. F2). Within Subunit 1A, pronounced wt% CaCO3 lows occur at 14.52, 24.02, and 33.63 mbsf with an approximate frequency of 9.5 per meter, the length an Ocean Drilling Program (ODP) advanced piston core. The carbonate low at 24.02 mbsf corresponds to a 4-cm-thick layer of dark sediment that begins at the top of Core 194-1198A-4H and is interpreted to result from material falling down the hole (i.e., "fall-in"). The carbonate lows near the tops of Cores 194-1198A-3H and 5H (14.52 and 33.63 mbsf, respectively) are not interpreted to represent fall-in because, unlike Core 194-1198A-4H, an upcore decreasing wt% CaCO3 trend exists.
Variations in bulk carbonate occur with a much higher frequency, between ~2 and 4 per meter. Based on biostratigraphic datum levels and sedimentation rates (Shipboard Scientific Party, 2002), this entire interval likely corresponds to the early Pleistocene "41-k.y. world."
Core 194-1198A-3H was analyzed within this study to provide a quantitative comparison between coulometry and the carbonate bomb method employed by Page (this volume). However, analyses were not performed on "splits" of the same sample (i.e., the core was separately sampled for each study). Nonetheless, the two data sets correspond well (Fig. F3). The major difference in the two data sets is that the carbonate low at 20.69 mbsf in the Page data set is not captured by this study, which is most likely because of differing sampling intervals. This study analyzed samples at 20.52 and 20.77 mbsf, encompassing but not directly sampling the interval of minimum wt% CaCO3 identified at 20.69 mbsf by Page (this volume).