SUMMARY AND CONCLUDING REMARKS

An analysis of Hole 1017E revealed the following:

1. TOC concentrations (24.8 ± 2.9 mg/g) in Holocene sections are higher than those in glacial sediments (14.2 ± 4.8 mg/g). The ¹³C of TOC (-21.3 ± 0.2) in the Holocene sections are higher than those in glacial sediments (-22.1 ± 0.1).
2. The positive shift by 0.8 in ¹³C of sedimentary TOC at ~10 ka might be explained by a positive shift in ¹³C of the dissolved CO₂ (~0.3) because of the increase in SST, a positive shift by 0.5 resulting from increase in growth rate of phytoplankton (probably planktonic primary productivity), and (partly) resulting from a drop in input of terrestrial higher plant-derived OM.
3. Sulfur concentrations are high in sections corresponding to anoxia Event 1 of warm interstadials (Behl and Kennett, 1996). The marked coincidence suggests that the same factor (the presence of relatively old bottom waters) played a role for both events. However, another anoxia event (Event 2 at 23.7-22.8 ka) does not correlate with high sulfur contents, and higher sulfur contents are not found in other sections. These results may indicate that short-term changes in oxygenation level occur rapidly and locally and are controlled by a complicated water current system in this region during glacial periods.

A detailed organic geochemical study at molecular level is in progress to gain further insight into the relation between oceanographic and terrestrial processes and global climatic events.