The opal concentrations at Sites 1095, 1096 and 1101 are plotted vs. depth in Figure F2 and vs. age in Figure F3. Figure F3 also includes time series of opal contents integrated linearly at time increments of 200 k.y.
At Site 1095, only two closely spaced samples taken from sediments, which are early late Miocene in age (562-510 mcd), were investigated for opal. Both samples revealed low opal contents on the order of 5 wt% (Figs. F2, F3). The low opal values might not be representative for the whole lower part of the upper Miocene sequence at Site 1095, but a low opal concentration is also indicated by low diatom abundance within this poorly recovered sequence (Barker, Camerlenghi, Acton, et al., 1999). The sediments spanning the middle and upper parts of the upper Miocene (510-178 mcd) are characterized by opal contents that predominantly vary between 8 and 20 wt% around a mean value of 13 wt%. Opal concentrations in this sequence are especially low in distinct samples in which partly recovered coarse-grained layers represent distal turbidites (e.g., at 199 mcd). The long-term trend in opal concentrations at Site 1095 exhibits a general decrease through the upper Miocene, with relative minima centered at ~7.8, ~6.6, and ~5.6 Ma.
The opal contents in sediments that are early Pliocene to early late Pliocene in age (178-90 mcd) predominantly fluctuate between 10 and 25 wt% around a relatively high mean value of 17 wt%. As in the older sediments, low opal amounts were measured in partly sampled distal turbidites. Within the rest of the upper Pliocene sequence (90-65 mcd), the mean opal contents exhibit a clear upward decrease with high frequent variations with an amplitude of 3 wt%. The Quaternary sediments (65-0 mcd) are separated from the upper Pliocene sequence by a hiatus. Opal contents in the Quaternary sediments, which have a temporal resolution of only ~50 k.y., vary around a mean value of 7 wt% with an amplitude of 5 wt%, thereby showing no significant long-term trend. Diatom abundances counted in samples taken from the upper Miocene to Quaternary sequence at Site 1095 exhibit a very similar pattern as the opal contents (Pudsey, Chap. 25, this volume).
At Site 1096, opal concentrations in sediments deposited during the early Pliocene and the early late Pliocene (589-305 mcd) exhibit opal fluctuations from 10 to 40 wt% around a mean opal value of 17 wt% (Figs. F2, F3). A significant decrease of the opal contents to a value of 3 wt% characterizes the rest of the upper Pliocene sequence (305-139 mcd). The amplitude of opal variations in these sediments is 3 to 5 wt%. The Quaternary sediments at Site 1096 (139-0 mcd) comprise a mean opal content of 3.2 wt%, superimposed by fluctuations with an amplitude of only 2 to 3 wt%. The opal contents within the Quaternary sequence exhibit a slight increase upward, reaching 7.8 wt% in the surface sediment sample. A similar increase is also observed in diatom abundance (Pudsey, Chap. 12, this volume). A sample taken at 114.8 mcd (178-1096B-13H-3, 45-47 cm) recovered exclusively a sandy turbidite, yielding an opal content of only 0.4 wt% (Fig. F2).
The opal contents in the upper Pliocene sequence at Site 1101 (216-121 rmbsf) show a systematic upward decrease from values higher than 10 wt% down to values on the order of 4 wt%. Small-scale fluctuations with an amplitude of ~5 wt% are superimposed on this trend. Within the Quaternary sediments at Site 1101 (121-0 rmbsf), the opal concentrations predominantly vary between 3 and 6.5 wt% around a mean value of 4.6 wt% and exhibit a slight increase, which was also observed at Site 1096. Opal contents at Site 1101 confirm diatom counts (Pudsey, Chap. 12, this volume).
The accumulation rates of biogenic opal (MARopal) at Sites 1095, 1096, and 1101 are plotted together with the LSR vs. age in Figure F4.
MARopal at Site 1095 shows a general decrease throughout the Neogene and Quaternary, varying from 25 g/m2 per yr during the early part of the late Miocene to 1 g/m2 per yr during the late Quaternary with some MARopal spikes of up to 60 g/m2 per yr occurring in the early part of the late Miocene. A positive correlation between MARopal and LSR is observed at Site 1095.
At Site 1096, MARopal slightly declined throughout the Pliocene from 40 g/m2 per yr during the early Pliocene down to 27 g/m2 per yr at 2.6 Ma. A major drop down to 12 g/m2 per yr in MARopal occurred at 2.6 Ma. Throughout the rest of the late Pliocene, MARopal slightly declined to 3 g/m2 per yr. Values on this order were obtained from the entire Quaternary section. The highest MARopal between 4.6 and 2.6 Ma are linked to LSRs higher than 15 cm/k.y.
At Site 1101, MARopal is 12 g/m2 per yr between 3.0 and 2.8 Ma and declines to 1 g/m2 per yr at 1.9 Ma. Throughout the Quaternary, mean MARopal at Site 1101 is 3 g/m2 per yr.