CONCLUSIONS

The oxygen and carbon isotope stratigraphies for Site 1144 were obtained from hemipelagic sediments collected from the northern continental slope of the SCS. The isotopic record covers a >500-m-long sediment profile spanning the last 1.1 m.y. from the early Pleistocene to the Holocene. The intense hemipelagic deposition is probably linked to both lateral advection of terrigenous sediments in the nepheloid layer and oscillating boundary current activity, leading to a thick drift-type deposit. On the basis of outstandingly high sedimentation rates near 50–100 cm/k.y., the sediment profile of Site 1144 provides a high-resolution record of stable isotope oscillations and monsoon history on orbital to centennial timescales over the last 1.1 m.y.

Our analysis of the Site 1144 ¹⁸O and ¹³C records led to the following conclusions:

1. Subsequent to MIS 27 (950 ka), the long-term paleoclimatic record is largely dominated by standard sawtooth pattern 100-k.y. cycles.
2. Several major and minor hiatuses interrupt the sediment profile, tied to peak interglacial Stages 5.5, 7.5 (reaching back to MIS 8.5), 9.1, 11.3, and 15.5. These stratigraphic gaps are also reflected in the seismic record. They possibly result from an intensified contour current regime along the lower continental margin of South China, controlled by incursions of Upper Pacific Deep Water, which were enhanced near the end of major glacial terminations.
3. Pronounced millennial-scale cycles dominate the short-term ¹⁸O variability in monsoon intensity over the last 900 k.y. During the last 110 k.y., the cycles closely match the climate variability of DO cycles as documented in the GISP2 ¹⁸O record. Similar high-frequency oscillations with comparable amplitudes in planktonic ¹⁸O are documented for MIS 6, lower 8–11, 12–15, and 16–24. Short-term climatic reversals similar to the YD are recorded within most glacial terminations, such as at the onset of warm MIS 5.5, 9.3, 11.3, and 19.
4. The planktonic carbon isotope record at Site 1144 shows long-term surface water ¹³C oscillations, which parallel the 100-k.y. eccentricity variations of the past 0.9 m.y. Moreover, ¹³C values form two 450-k.y. cycles culminating at ~30, ~480, and ~1035 ka. The variations in ¹³C are a global feature also seen in the North Atlantic and possibly result from oscillations in East Asian monsoon intensity, which controls local changes in wind stress and riverine nutrient supply and thus is responsible for the advection of nutrient-enriched surface water and/or the discharge of ¹³C-depleted terrestrial organic carbon.