Millennial-scale changes in terrestrial sediment input and Holocene surface hydrography in the northern South China Sea (IMAGES MD972146)

Abstract

This study presents a high-resolution, multi-proxy analysis of sediments from IMAGES core MD972146 in the northern South China Sea (SCS). Analyses include detailed measurements of planktonic foraminifer oxygen isotopes, sediment carbonate, total organic carbon (TOC), opal, and phosphorus concentrations, as well as a Holocene interval of planktonic foraminifer sea surface temperature (SST) estimates. The age model of MD972146 was constructed by adopting oxygen isotope stratigraphy and AMS 14C dating, and fine-tuned further by correlation with nearby, well-studied SONNE 17940 and Hulu stalagmite isotope records. The age model indicates that this record covers the past 70,000 yr—from isotope stage 4 to the Holocene—with a nearly constant, very high sedimentation rate of ∼50 cm/kyr. Such sedimentation rates allow for intensive investigations of millennial-scale climate variability expressed in the SCS and its potential global linkages. We constructed a composite terrestrial index (CTI) for MD972146 through a principal component analysis of a suite of the core proxies that are sensitive to terrestrial sediment input. During the last glacial of stage 4 to stage 2, warm interstadials appear to coincide with high terrestrial sediment pulses inferred from the CTI, suggesting humid conditions in the SCS and Southern China. Intervals of high terrestrial input are also correlated with Heinrich events, suggesting an increase of eolian and possibly also of fluvial terrestrial input to the northern SCS. Our high resolution Holocene SST and salinity estimates show warm, stable and humid conditions during short episodes of quasi-periodic, millennial-scale cooling in the North Atlantic, superimposed on generally more humid conditions during the middle Holocene (4–6 ka) compared to the dry late Holocene (0–4 ka). The presented data provide evidence that a variety of mechanisms involving the strength of East Asian summer monsoons, migration of the Intertropical Convergence Zone, and processes that are analogous to those governing the El Niño Southern Oscillation and the Arctic Oscillation might play important roles in modulating tropical climate during the last glacial stages and the Holocene.