Values of mean grain size plotted vs. time in Figure F3A show limited variations between 6 and 28 µm, which are mostly silt size. However, a detailed examination of this curve indicates that interglacial stages are characterized, on average, by slightly finer grains (~10-15 µm for MIS 1, 5, 7, 9, 11, 13, 15, 19, 21, and 23) than glacial periods (~16-26 µm for MIS 2, 3, 4, 6, 10, 12, 16, 20, and 22). Besides, a long-term increase in grain-size can be observed prior to 600 ka. Such glacial-interglacial variations are confirmed on Figure F4, which shows different grain size distributions for interglacial (Holocene; 5.7 mcd) and glacial (Stage 6; 166.7 mcd) samples.
Previous studies on grain size variations (e.g., Wang et al., 1999) have used the standard grain size classification (clay = <6 µm and silt = 6 to >63 µm) to represent grain size variations through time. Here, we propose a new method, permitting easy identification of the grain size intervals with the highest variability along a sedimentary sequence. For each 30 grain size classes given by the Malvern Mastersizer, standard deviations were calculated for our 300 samples. Standard deviation values vs. grain size classes are displayed on Figure F5. Two peaks are observed in this plot, at 2.5- to 5- and 20- to 40-µm grain size intervals, respectively. Each of these size classes represents a population of grains with the highest variability through time. On the other hand, for instance, the intermediate 8- to 12.5-µm size class is characterized by low standard deviation values, implying no important change of the proportion of this grain size population in the siliciclastic fraction. This result is confirmed by the variations of the 2.5- to 5-, 8- to 12.5-, and 20- to 40-µm size class proportion (percent) through time (Figs. F4, F3B). Both the 2.5- to 5- and 20- to 40-µm grain size populations vary significantly with climate changes. No significant variation can be observed in the 8- to 12.5-µm grain size population (Fig. F3B). Long-term fluctuations of the 2.5- to 5-µm size class distribution are inversely correlated to those of the 20- to 40-µm size class. Interglacial stages are characterized by higher proportions of the 2.5- to 5-µm size interval than glacial stages.
Throughout the entire Site 1144 sediment sequence, illite and chlorite are the dominant clay minerals and are in the range of 30%-60% and 15%-35% of the <2-µm clay mineral fraction, respectively (Fig. F6A). Smectite and kaolinite are of secondary importance, reaching values of 0%-30% and 5%-25%, respectively. These ranges are close to those observed for Site 1146 (Trentesaux et al., this volume).
Over the last 400 k.y. no major change in clay mineral composition was recorded. There is a slight increase in chlorite during glacial Stages 2, 3, 6, and 10. There appears also to be a slight increase (decrease) in smectite (illite) during isotopic events 1, 3, 5.1, and 7.1, resulting in an increase of the smectite/(illite + chlorite) ratio.
Quartz and carbonate contents of the bulk fraction were determined by FTIR spectroscopy on 29 samples to compare the proportion of quartz with grain size and major element results. Quartz proportions were corrected for carbonate dilution using the following relationship:
Quartz proportions vary significantly with climate changes (Fig. F6B). Observed values are lower during MIS 1, 4, and 5 than during MIS 2, 3, and 6.
Major element content analyses were performed on 87 samples (Fig. F7). CaO, Na2O, TiO2, and FeO do not present any significant variation during glacial-interglacial changes and range between 0.3 and 1.7, 1 and 1.6, 1 and 1.3, and 4 and 7.3 wt%, respectively. On the contrary, SiO2, Al2O3, K2O, and MgO contents vary significantly with climatic changes from 64 to 73, 15 to 20, 2.9 to 4.3, and 1.6 to 2.8 wt%, respectively. Al2O3, K2O, and MgO display the same behavior, with an increase during interglacial Stages 1 and 5 and a decrease during glacial Stages 2, 3, 4, and 6. MIS 6.5 is also characterized by an increase of these elements. SiO2 percent variations are opposite from those of Al2O3 and K2O. Normalization to aluminum is commonly used to characterize terrigenous sediments. SiO2/Al2O3 and K2O/Al2O3 as well as SiO2/K2O ratios are displayed on Figure F8. Interglacial Stages 1 and 5 are characterized by lower values of the SiO2/Al2O3 and SiO2/K2O ratios than during glacial Stages 2, 3, 4, and 6. The K2O/Al2O3 ratio does not exhibit any significant variation along the entire record.