Sea Surface Temperature, Productivity, and Terrestrial Flux Variations of the Southeastern South China Sea over the Past 800000 Years (IMAGESMD972142)

Abstract

Variations in sea surface temperature (SST), productivity, and biogenic components such as total organic carbon (TOC), carbonate, and opal contents measured from IMAGES (International Marine Global Changes Study) core MD972142 provide information about long-term paleoceanographic changes during the past~870000 years in the southeastern South China Sea (SCS). MD972142 U 37 k' -SSTs varied from 25 to 29°C, paralleling the glacial to interglacial changes. MD972142 biogenic components show relatively high carbonate and opal, and low TOC contents in interglacial stages, and low carbonate and opal and high TOC contents in glacial stages, and these variations appear to be sensitive to regional terrestrial sediment input and productivity. Our analysis indicates that the MD972142 carbonate record is primarily controlled by terrestrial sediment inputs that are associated with sea level fluctuations during past glacial-interglacial stages. The TOC record reflects past glacial-interglacial changes in both monsoon-induced productivity and terrestrial organic matter input in the SCS. The TOC record exhibits several short-term peaks that are associated with lower U 37 k' -SSTs (especially in MIS 2 -4, 10, 12), perhaps implying a much strengthened winter monsoon. The opal record shows relatively high content in most interglacial stages, which appears to be linked to increased summer monsoon upwelling or increased siliceous sediment input by more precipitation and river runoff during warm climate conditions. The TOC and opal contents both show long-term increasing trends since the mid-Brunhes, most noticeably from~330 kya. The long-term trends observed in this study are most likely attributable to changes in SCS hydrography, productivity, and/or preservation in response to the increased strength of the East Asian monsoon system on possibly tectonic timescales.

Circulation and oxygenation of the glacial South China Sea

“…For the southeastern SCS, TOC and organic biomarkers indicate higher primary productivity during glacial periods being ascribed to stronger EAWM Shiau et al, 2008). As 5 aforementioned, our model case in glacial condition favors vigorous diapycnal mixing to support paleorecords of increased primary productivity.…”

“…In fact, Mn content in core MD972142 was determined by XRF (X-ray fluorescence spectrometer) and had been reported by Löwemark et al (2009); however, our ICP-OES provide more 20 quantitative result. Total organic carbon (TOC) reported by , C37 Alkenones by Shiau et al (2008) and planktonic foraminiferal δ 18 O by Wei, K. Y. et al (2003) were drew for discussion.…”

Introduction to the Special Section “Proxy Records and Mechanistic Studies of the Late Quaternary Paleoceanography of the Western Pacific Marginal Seas Using IMAGES Cores”

“…The MD972142 results nicely demonstrate that more records using biomarkers as community structure proxies can help resolve some of these questions. Shiau et al (2008) also observed a long-term increased trend in all productivity proxies since the mid-Brunhes. This, coupled with the MD012380 record from the Sulu Sea , suggests a change in the tropical western pacific, probably in response to the increased strength of the East Asian monsoon system.…”

“…However, it is not clear why the opal content was lower during the glacials. If one assumes that the opal content is purely a proxy for diatom productivity, then the results by Shiau et al (2008) imply that there was a major phytoplankton community structure change for the site during glacial-interglacial cycles. It can be inferred from their data that diatom contribution to total productivity was lower during the glacials when the total productivity was higher, and its contribution was higher during the interglacials when total productivity was lower.…”

“…One explanation for these differences is that the alkenone index records annual SST; this index is less sensitive to summer monsoon variability. Longer (870 kyr) and multi-proxy records allow Shiau et al (2008) to better evaluate both the summer and winter monsoon variabilities and phase relationship. They reported high resolution records for core MD972142 from the southeastern SCS, which include SST, productivity (TOC, opal and alkenone contents) and terrestrial components.…”