Luejiang Wang

High‐resolution UK 37 temperature reconstructions in the South China Sea over the past 220 kyr

Past sea surface temperatures (SST) in the northern and southern areas of the South China Sea have been reconstructed for the past 220 kyr using the UK37 alkenone index. The SST profiles follow the glacial/interglacial pattern exhibiting differences between Last Glacial Maximum and Holocene that are 1°–3°C larger than those observed at the same latitudes in the Atlantic and Pacific Oceans. In Termination I both planktonic foraminiferal δ18O and SST exhibit well-defined Bolling-Allerod and Younger Dryas events with temperature differences between both periods of 0.8° and 0.4°C in north and south, respectively. SSTs record a constant north-south difference of 1°C in the interglacials and nearly 2.5°C in the glacial stages. These differences define two distinct climatic and water circulation patterns that correspond with glacial/interglacial sea level oscillations which opened and closed water exchange with the tropical Indo-Pacific Ocean through the present Sunda Shelf.

Benthic foraminiferal paleoceanography of the South China Sea over the last 40,000 years

Benthic foraminifera in gravity and piston cores from two sites of the northern and southern slopes of the South China Sea (SCS) were analyzed to evaluate changes in surface productivity and deep-water mass characteristics over the last 40,000 years. Our observations suggest that changes in organic carbon flux, that is food supply, and chemical and=or physical properties of the ambient water mass may be the two primary and intercorrelated factors controlling the distribution patterns of benthic foraminifera. When organic carbon flux increased above 3.5 g C m 2 yr 1 in the southern SCS during the last glacial maximum and in the northern SCS during the first part of the Holocene around 10 ka B.P., a group of detritus feeders including Bulimina aculeata and Uvigerina peregrina dominated the benthic foraminiferal assemblage as shown by relative abundance (%) and accumulation rates. This may reflect episodes of increased surface productivity, possibly induced by increased input of nutrients from nearby river runoff. Suspension feeders such as Cibicidoides wuellerstorfiand a group of ‘opportunistic’ species including Oridorsalis umbonatus, Melonis barleeanum and Chilostomella ovoidea gradually became more abundant than detritus feeders as soon as the organic carbon flux decreased to 2.5‐3.5 g C m 2 yr 1 . Similar glacial to interglacial changes in relative abundance and accumulation rates were observed in both cores for a number of species, including Eggerella bradyi, Globocassidulina subglobosa , Astrononion novozealandicum , Sphaeroidina bulloidesand Cibicidoides robertsonianus. These changes were not correlated to the distribution patterns of organic carbon in both cores and may have been related to yet unspecified changes in chemical and=or physical properties of the ambient water mass, independent of changes in organic carbon flux.

Holocene variations in Asian monsoon moisture: A bidecadal sediment record from the South China Sea

The East Asian monsoon system involves extensive transport of sensible/latent heat between land and sea and from low to high latitudes. Our high resolution, bidecadal marine records present a first detailed history of monsoon climate change over the Holocene. The high-amplitude perturbation in monsoon moisture centered at 8,150 years ago and the monsoon maximum in the Early Holocene show inter-hemispheric teleconnections to both a cool episode in Greenland and to the Indian monsoon monitored in the Arabian Sea. Periodicities of 84, 102 and, especially, near 775 years in monsoon variation suggest a climatic forcing both by long-term oscillations in thermohaline circulation and (possibly) solar activity cycles.

Paleo sea surface salinities in the low‐latitude Atlantic: The δ18O record of Globigerinoides ruber (white)

On the basis of the comparison of δ18O values of Globigerinoides ruber (white) (δ18OG. ruber) from modern sediments and measured sea surface temperatures (SST) and salinity (SSS), δ18OG. ruber values most clearly record summer SST and SSS of the uppermost 50 m of water in the low-latitude Atlantic. A new transfer equation is presented for estimating local summer paleo SSS at 0–50 m depth using δ18OG. ruber, paleo SST, and the global δ18O ice effect of sea water, with the standard error reaching ±0.72 - ±0.77‰ SSS. The equation was applied to a 35 kyr long δ18OG. ruber record and paleo SST estimates based on planktonic foraminiferal assemblages to reconstruct the paleo SSS changes along the east Atlantic margin off the northwest Sahara. The resulting local SSS show a general increase by 0.3–1.4‰ during the last glacial maximum (LGM) and large parts of glacial Termination I, suggesting a general increase in the upwelling of the highly saline North Atlantic Central Water and/or a reduced lateral advection of less saline Canary Current water. Two short salinity lows (up to 0.35‰ less than today) during and after the LGM are coeval with the Heinrich meltwater events 1 and 2 in the North Atlantic, indicating the breakdown of coastal upwelling and meltwater advection from the north. Both events are followed by an extreme SSS maximum (38.15‰) along with the restoration of the salinity conveyor belt. At 9.0–5.5 ka the salinity minimum (up to 0.65‰ less than today) reflects the continental runoff linked to the phase of strong North Saharan humidity during the early Holocene climatic optimum.

The flooding of Sundaland during the last deglaciation: imprints in hemipelagic sediments from the southern South China Sea

Abstract During the last 30 ka, the South China Sea (SCS) experienced pronounced palaeogeographic changes associated with the postglacial sea level rise, which significantly modified the hydrography of this marginal sea. The most crucial effects in the southern part of the basin were the submergence of Sundaland and the opening of the southern channels connecting the SCS to the tropical Indo-Pacific. Isotopic, sedimentological and organic geochemical parameters determined in two sediment cores from the southern SCS, one in the open sea and the other close to the continental shelf (sites 17961 and 17964, respectively) show that the main hydrographical changes during this period were related to critical thresholds in sea level rise. The main changes occurred at about 15–13.5 ky BP, coincident with Meltwater Pulse (MWP) Ia, when sea surface temperatures (SSTs) at both sites experienced a rapid 1.5°C rise, and the clay content and n-nonacosane concentrations dropped significantly. Both trends reflect a rapid retreat of the coastline and an initial flooding of Sundaland at that time. A second important change, starting with the beginning of MWP Ib at about 11.5 ky BP and culminating at 10 ky BP, involved the establishment of modern hydrographic conditions. This is evident from the rapid convergence of the foraminiferal oxygen isotope records and the establishment of Holocene SST values. These results highlight the need to include the flooding/emergence of Sundaland as an important boundary condition in future modelling studies of Asian palaeomonsoons.

Molecular biomarker record of sea surface temperature and climatic change in the South China Sea during the last 140,000 years

The d 18 Oa ndd 18 C isotopic composition of Globigerinoides ruber, the concentration of C37 alkenones, n-nonacosane and n-hexacosan-1-ol and the populations of coccolith species in core 17961-2 have been used to characterize the climatic changes which occurred in the South China Sea (SCS) during the last climatic cycle. The relative composition of diand triunsaturated C37 alkenones, the U K index, has been used to estimate the variation in sea surface temperatures. The concentrations of the terrigenous markers n-nonacosane and n-hexacosan-1-ol have allowed to infer changes in continental water dynamics during the glacial and interglacial times. The stratigraphic record of these compounds has shown that the influence of continental waters (i.e., the Molengraaff River) and restricted water circulation in SCS gave rise to a marginal system of higher but slower response to climatic change. Both in terminations I and II, the change from glacial to interglacial conditions involves a considerable reduction of continental water input into this semi-enclosed system. The high resolution study of the biomarker proxies in Termination I has shown that the SST increase lagged about 2.3 ky the d 18 O isotopic decrease of Cibicidoides wuellerstorfi . Probably, the SST increase corresponds to the period of the Sunda Shelf inundation onset.

Millennial reoccurrence of century-scale abrupt events of East Asian Monsoon: A possible heat conveyor for the global deglaciation

High-resolution sediment records from the South China Sea reveal a winter monsoon dominated glacial regime and a summer monsoon dominated Holocene regime during the last glacial cycle. A fundamental change between regimes occurred during deglaciation through a series of millennial reoccurrences of century-scale changes in the East Asian monsoon (EAM) climate. These abrupt events centered at 17.0, 15.9, 15.5, 14.7, 13.5, 13.9, 13.3, 12.1, 11.5, and 10.7 14C ka correlate well with the millennial-scale events in the Santa Barbara Basin and the Arabian Sea, i.e. a relationship between EAM and El Nino/Southern Oscillation systems. The abrupt increases in summer monsoon imply enhanced heat transport from low-latitude sea area to the midlatitude/high-latitude land area. The phase relationship between events of EAM and ice sheet may reflect a faster EAM response and a slower ice sheet response to the insolation change. A far-reaching conclusion is that the EAM might have triggered the Northern Hemisphere deglaciation.

Long-/Short-Term Variations of Monsoon Climate and its Tele-Connection to Global Change

Core 17940-1/2 (20°07′N, 117°23′E; 1727-1728m water depth) from the South China Sea provides a high resolution marine sediment record, up to bidecadal in the Holocene and 80–100 years in last glacial time, for reconstructing the East Asian monsoon climate change during the past 41,000 years. A fundamental change happened in the monsoon climate during the last deglaciation, when the winter monsoon dominated glacial regime changed to a summer monsoon dominated Holocene regime. Comparison to the GISP2 ice core record suggested climatic tele-connections between the low latitude East Asian Monsoon climate and that over the high latitude Greenland during the last glacial period. Episodic short-term periods of increased summer monsoon precipitation and decreased winter monsoon wind intensity are correlated to the warm periods of Dansgaard-Oeschger events 1–10. Periods of relatively intensified winter monsoon wind and reduced summer monsoon precipitation are correlated to the Heinrich events 1–4. The possible link in this tele-connection is believed to lie in the oscillation in atmospheric circulation rather than oceanic thermohaline circulation, with a counterbalance between the westerlies and the monsoon wind. Whenever the high latitude polar Greenland was warmed up, the westerlies may have been reduced in strength and/or extension. Consequently, it is postulated that the summer monsoon circulation would have culminated in East Asia due to the increased contrast in land-sea air pressure during summer, when the low pressure cell over mid-high latitude land areas was intensified due to the high-latitude warming. The opposite scenario is suggested for the Heinrich events. In addition, an intra-hemispheric joint forcing is evidenced for the Early Holocene-Preboreal summer monsoon maximum between 11,600–8,800cal. yBP, based on the synchrony of the events found both in the South China Sea and in the Arabian Sea. The unique early Holocene polar cooling event at about 8,200cal. yBP recorded in the Greenland ice core is found to coincide with a large-scale perturbation in the low latitude summer monsoon precipitation.