The coarse fraction of most Site 1143 sediment samples is <5 wt%, with only two values above this range (Fig. F1). No obvious trend is observed within the data set. Site 1143 CaCO3 concentrations vary between 59.02 and 6.03 wt%. The sediment contents of CaCO3 are higher below 300 meters composite depth (mcd) than above but gradually decrease from ~60 wt% at 310 mcd to the minimum at 18 mcd. The variability pattern of CaCO3 is generally different from that of the coarse fraction. Most of the TOC concentrations are <0.5 wt%, with only three values considerably greater. The increasing trend from 200 mcd to core-top sediments mirrors that of CaCO3, suggesting that the CaCO3 concentrations reflect varying amounts of noncarbonate hemipelagic sediment input (e.g., clastics and admixed volcanic ash) (Wang, Prell, Blum, et al., 2000).
Site 1146 coarse fractions range between 21.21 and 1.02 wt% (Fig. F2). In general, the values are lower for sections below 420 mcd and in the upper 200 m. It cannot be ruled out that this is an artifact resulting from the different sampling resolutions along the core for this study. The concentrations of CaCO3 at Site 1146 vary between 28 and 18 wt% below 570 mcd and then increase gradually to reach a plateau of ~60 wt% at ~415 mcd. CaCO3 contents remain high uphole to ~255 mcd and then decline to a minimum at the top of the sediment core, with the exception of the peak between 255 and ~415 mcd. With few exceptions, the downcore record of coarse fraction mimics that of CaCO3 at Site 1146, implying that the carbonate shells of microfossils are the major contributors for the sand fraction in core sediments. Site 1146 TOC values are consistently <0.3 wt% from ~200 mcd downhole to the bottom of the core. A progressive increase in TOC occurs between 200 and 60 mcd, followed by a rapid increase to the maximum of 1.21 wt% at the top of the core.
A tentative comparison between the time series of these two records was made according to preliminary age models based on the biostratigraphy and paleomagnetism measured on board (Fig. F3) (Wang, Prell, Blum, et al., 2000). Because this study yielded only seven data points older than 10 Ma for Site 1146 and Site 1143 has a depositional history of only 9 m.y., we compare coarse fraction, CaCO3, and TOC between the two sites for the last 10 m.y., as shown in Figure F3. In general, the coarse fraction and CaCO3 from Site 1146 are higher than those of Site 1143 for sediments older than Quaternary. The Site 1143 CaCO3 begins to decrease gradually at 7 Ma, yet at Site 1146 it remains constant until 4 Ma and then decreases rapidly until ~1 Ma (Fig. F3). Of special interest is the fact that although the CaCO3 contents are similar in the upper Miocene sections of these two sites, the accumulation rate of CaCO3 at Site 1143 is almost twice as high as that at Site 1146 (Fig. F4). The high accumulation rate of CaCO3 at Site 1143 during the late Miocene reflects an increased sedimentation rate, which has been ascribed to the redeposition of adjacent sediments (Wang, Prell, Blum, et al., 2000). Whether this is the signature of the "biogenic bloom" recorded in the equatorial Pacific regime (e.g., Berger et al., 1993; Farrell et al., 1995) has yet to be confirmed. Furthermore, in contrast to the steadily decreasing CaCO3 accumulation rates at Site 1143 since 7 Ma (Fig. F4), CaCO3 accumulation rates at Site 1146 remain within a relatively narrow range throughout the record.
Site 1146 TOC concentrations are lower than those from Site 1143 (Fig. F3) except for the interval after ~2 Ma. Nevertheless, the variation patterns are similar, with consistently low values prior to ~4 Ma and then increasing values to the present.