(Table T1) Long-chain alkenones, UK'37 and derived sea surface temperatures of ODP Sites 184-1147 and 184-1148

A reconnaissance study of alkenone stratigraphy for the past 35 m.y. in the northern South China Sea (SCS) using sediments from Sites 1147 and 1148 of Ocean Drilling Program (ODP) Leg 184 has been completed. Alkenones were not detected in sediment samples older than ~31 Ma. However, C37:2 appeared in the sedimentary record between ~8 and 31 Ma and both C37:2 and C37:3 were present between 0 and 8 Ma. These changes in alkenone occurrences may signal a response to global-scale Neogene cooling as well as to monsoon intensification and sea level changes over time as a result of Himalayan uplift and the opening of the SCS. Alternatively, they may be related to an evolutionary record of the development of temperature control on alkenone production in coccolithophores. The Uk'37 index for 0-8 Ma produces sea-surface temperatures (SST) of 19°-26°C, which are in the range of previously determined glacial-interglacial values for the northern SCS. Before the late Pleistocene (~1.2 Ma), the SST range is between 23° and 26°C with less variation. This change in variability may signify the early stage of intensified winter monsoons where cold wind and waters from the north may not yet have had a significant effect on SST or it may be the evolutionary link between the early development of unsaturated alkenones in coccolithophores and modern temperature control of alkenone production. We believe a long-term alkenone record is useful for further understanding of global-scale neogene cooling, the development of the East Asian monsoon system, and the evolutionary development of temperature control on alkenone unsaturation. Our data indicate that a high-resolution Uk'37 record for at least the last ~8 Ma is feasible for the northern SCS.

Age model of ODP Site 184-1146 (Table 1)

Clay mineral assemblages at ODP Site 1146 in the northern South China Sea are used to investigate sediment source and transport processes and to evaluate the evolution of the East Asian monsoon over the past 2 Myr. Clay minerals consist mainly of illite (22-43%) and smectite (12-48%), with associated chlorite (10-30%), kaolinite (2-18%), and random mixed-layer clays (5-22%). Hydrodynamic and mineralogical studies indicate that illite and chlorite sources include Taiwan and the Yangtze River, that smectite and mixed-layer clays originate predominantly from Luzon and Indonesia, and that kaolinite is primarily derived from the Pearl River. Mineral assemblages indicate strong glacial-interglacial cyclicity, with high illite, chlorite, and kaolinite content during glacials and high smectite and mixed-layer clay content during interglacials. During interglacials, summer enhanced monsoon (southwesterly) currents transport more smectite and mixed-layer clays to Site 1146 whereas during glacials, enhanced winter monsoon (northerly) currents transport more illite and chlorite from Taiwan and the Yangtze River. The ratio (smectite+mixed layers)/(illite+chlorite) was adopted as a proxy for East Asian monsoon variability. Higher ratios indicate strengthened summer-monsoon winds and weakened winter-monsoon winds during interglacials. In contrast, lower ratios indicate a strongly intensified winter monsoon and weakened summer monsoon during glacials. Spectral analysis indicates the mineral ratio was dominantly forced by monsoon variability prior to the development of large-scale glaciation at 1.2 Myr and by both monsoon variability and the effects of changing sea level in the interval 1.2 Myr to present.

(Table 1) Element concentrations in detrital sediments of ODP Site 184-1148

The chemical index of alteration (CIA) and elemental ratios that are sensitive to chemical weathering, such as Ca/Ti, Na/Ti, Al/Ti, Al/Na, Al/K, and La/Sm, were analyzed for detrital sediments at Ocean Drilling Program Site 1148 from the northern South China Sea to reveal information of chemical weathering in the source regions during the early Miocene. High CIA values of ~80, coupled with high Al/Ti and Al/Na and low Na/Ti and Ca/Ti, are observed for the sediments at ~23 Ma, indicating a high chemical weathering intensity in the north source region, i.e., south China. This was followed by gradual decreases in Al/Ti, Al/Na, La/Sm, and Al/K ratios, as well as the CIA values, and increases in Ca/Ti and Na/Ti ratios. These records together with other paleoclimate proxies, such as black carbon d13C and benthic foraminifer d18O, give reliable information on the climate changes in south China. Our results show that the climate in south China was warm and humid in the early Miocene (~23 Ma) according to the chemical weathering records. The humidity in south China decreased from the early Miocene to Present with several fluctuations centering at approximately 15.7 Ma, 8.4 Ma, and 2.5 Ma, coincident with the global cooling since the middle Miocene. These climate changes implied that the summer east Asian monsoon has dramatically affected south China in the early Miocene, whereas the influence of the summer monsoon on this region has decreased continuously since that time, probably because of the intensification of the winter monsoon. Such an evolution for the east Asian monsoon is different from that for the Indian monsoon.

Water temperature reconstructions based on paired Uk'37 and Tex86 records, and paired surface and subsurface Mg/Ca records

This dataset contains the collection of available published paired Uk'37 and Tex86 records spanning multi-millennial to multi-million year time scales, as well as a collection of Mg/Ca-derived temperatures measured in parallel on surface and subsurface dwelling foraminifera, both used in the analyses of Ho and Laepple, Nature Geoscience 2016. As the signal-to-noise ratios of proxy-derived Holocene temperatures are relatively low, we selected records that contain at least the last deglaciation (oldest sample >18kyr BP).

(Table T1) N-alkane, n-alcohol and n-fatty acid concentrations in ODP Site 184-1147 and 184-1148 sediments

Lipid compositions of sediments recovered during Ocean Drilling Program Leg 184 in the South China Sea have been identified and quantified. The identified lipids can be ascribed to terrigenous and marine sources. Terrigenous lipids are mainly C27, C29, C31 n-alkanes, C26, C28, C30 n-fatty acids, and n-alcohols, which were derived from leaf waxes of higher land plants and transported to the sea by airborne dust or fresh water. Marine lipids, mainly C37 and C38 alkenones, C30 diol, and C30 and C32 keto-ols, were from microalgae, notably haptophytes and eustigmatophytes. Elevated concentrations and accumulation rates of both terrigenous and marine lipids in the interval 202-245 meters composite depth (mcd) and 0-166 mcd were postulated to be related to the development of the East Asian monsoon at 6-8 Ma and enhanced variations of the developed East Asian monsoon after 3.2 Ma, respectively. The pronounced late Oligocene input of terrigenous lipids reflects the paleoenvironment of a newly opened, narrow basin, with restricted ocean waters and the proximity of continental runoff.

(Table 1) Radiolarian accumulation rates and geochemistry of ODP Site 184-1143

Late Miocene-Recent micropaleontological and geochemical records from Ocean Drilling Program (ODP) Site 1143 in the southern South China Sea (SCS) indicate that increase and decrease in abundance of siliceous plankton may be controlled mainly by the input of nutrients derived from land and provided by upwelling. A high export production event - a "biogenic bloom" event - occurred in the southern SCS between 12 and 6 Ma. During this period, high ratios of smectite/(illite + chlorite), smectite/quartz and Al/K indicate a high weathering intensity of the Asian continent, possibly due to the intensification of the East Asian Summer Monsoon (EASM), which may have increased the net flux of nutrients to the ocean, both directly through terrestrial input and indirectly through upwelling activity. A drop in Ba/Ti, Al/Ti and Ca/Ti values around 6 Ma may indicate a lowering of productivity, possibly due to the large consumption of sea surface nutrients by the "biogenic bloom". Alternatively, it may indicate a shift in terrigenous input source area. At about 5.4 Ma, a decrease in weathering intensity, as indicated by a sudden decrease in the values of smectite/(illite + chlorite), smectite/quartz and Al/K, might have led to a sudden decrease of terrestrial nutrient input to the SCS. We suggest that the biogenic bloom ended when nutrients in surface waters were exhausted, because of a decrease in supply as well as a decrease in upwelling intensity due to weakening of the EASM. As a result, radiolarians were absent in the studied area between ~6 and 3.2 Ma. At ~3.2 Ma, radiolarians began to recover, possibly because the start of Northern Hemispheric glaciation and the rapid uplift of the Tibet Plateau led to intensification of the East Asian monsoon. After the Mid-Pleistocene Climate Transition at 0.9 Ma, the abundance and mass accumulation rates of radiolarians increased, probably as a result of increased upwelling activity driven by the increasing intensity of the summer monsoon.

Stable isotope, UK'37, SST, chlorin, alkenone and TOC data of sediment cores GIK17927-2 and GIK17928-3

Upwelling intensity in the South China Sea has changed over glacial-interglacial cycles in response to orbital-scale changes in the East Asian Monsoon. Here, we evaluate new multi-proxy records of two sediment cores from the north-eastern South China Sea to uncover millennial-scale changes in winter monsoondriven upwelling over glacial Terminations I and II. On the basis of U/Th-based speleothem chronology, we compare these changes with sediment records of summer monsoondriven upwelling east of South Vietnam. Ocean upwelling is traced by reduced (UK'37-based) temperature and increased nutrient and productivity estimates of sea surface water (d13C on planktic foraminifera, accumulation rates of alkenones, chlorins, and total organic carbon). Accordingly, strong winter upwelling occurred north-west of Luzon (Philippines) during late Marine Isotope Stage 6.2, Heinrich (HS) and Greenland stadials (GS) HS-11, GS-26, GS-25, HS-1, and the Younger Dryas. During these stadials, summer upwelling decreased off South Vietnam and sea surface salinity reached a maximum suggesting a drop in monsoon rains, concurrent with speleothem records of aridity in China. In harmony with a stadial-to-interstadial see-saw pattern, winter upwelling off Luzon in turn was weak during interstadials, in particular those of glacial Terminations I and II, when summer upwelling culminated east of South Vietnam. Most likely, this upwelling terminated widespread deep-water stratification, coeval with the deglacial rise in atmospheric CO2. Yet, a synchronous maximum in precipitation fostered estuarine overturning circulation in the South China Sea, in particular as long as the Borneo Strait was closed when sea level dropped below -40 m.

Age determination of sediment core GIK16523-1

High-resolution studies of a planktonic foraminifer core record from the South China Sea (SCS) (31KL: 18°45.4'N, 115°52.4'E, water depth 3360 m) reveal changes driven by ice-volume forcings in the climate of the East Asian monsoon in the western Pacific marginal sea during the late Quaternary. The analyses of planktonic foraminifer faunal abundance data from the core indicate significant variations in the relative abundances of the dominant taxa over the past 100,000 years since the isotope stage 5. The transfer function estimates of faunal sea surface temperatures (SST) correlate well with a long-term (104-105 years) trend of global glaciation. About 65,000 years ago, there was an observable change in the mode of SST variability as many low-latitude records have shown. These findings suggest that the SCS surface circulation and the East Asian winter monsoon systems are mainly driven by variations in global glaciation levels. The association of surface ocean cooling in the SCS with global climatic events suggests that fluctuations in the strength of the East Asian winter monsoon may be linked to shifts in the latitudinal position of the westerly winds and the Siberian high-pressure system.

Calcareous nannofossils and planktic foraminiferal assemblages of ODP Hole 198-1210A

Calcareous nannofossil and planktic foraminiferal assemblages from ODP Hole 1210A in the northwestern Pacific Ocean were used to reconstruct surface-water conditions for the past 500 kyr. Stratigraphic control was provided by calcareous nannofossil events that are thought to be synchronous over a broad range of latitudes. Calcareous nannofossil and planktic foraminiferal assemblages and abundance patterns indicate the unlikelihood of long term (Milankovitch-scale) latitudinal shifts of the Kuroshio Extension over the last 500 kyr and illustrate two successive surface water-mass states, one that prevailed prior to 300 ka and one that existed after 300 ka. The relative abundance of very small placoliths and the absolute abundance of the upper photic zone (UPZ) coccolith species decrease abruptly at approximately 300 ka. The relative abundance of the lower photic zone (LPZ) species Florisphaera profunda greatly increases at the same time, although intervals during which the relative abundance of this taxon is very low or absent also occur prior to 300 ka. The absolute abundance of planktic foraminifera gradually increased after the 300-ka boundary, including peaks of Globoconella inflata. These assemblage and abundance changes suggest significant modifications to the surface water-mass structure. Surface water was weakly stratified prior to 300 ka, but alternated between intensely stratified and vertically mixed after 300 ka. Changes in the surface water-mass structure suggest an intensification of the East Asian summer and winter monsoon after 300 ka.

Stable carbon and oxygen isotope ratios of foraminifera in surface sediments of the South China Sea

The relationship between planktonic and benthic foraminiferal stable-isotope values and oceanographic conditions and factors controlling isotopic variations are discussed on the basis of oxygen and carbon isotopic analyses of 192 modern surface and Last Glacial Maximum (LGM) samples from the South China Sea (SCS). The harmonic variation of benthic delta18O in surface sediments with water depth and temperature implies that the temperature is the main factor influencing benthic delta18O variations. Planktonic delta18O fluctuates with sea surface temperature (SST) and salinity (SSS). The N-S temperature gradient results in planktonic delta18O decreasing from the northeast to the south. Cool, saline waters driven by the winter monsoon are interpreted to have been responsible for the high delta18O values in the northeast SCS. The East Asian monsoons not only bring nutrients into the South China Sea and maintain high nutrient concentration levels at the southwestern and northeastern ends, which cause depleted delta13C both in planktonic (surface) and benthic (bottom) samples but also reduce planktonic/benthic delta18O differences. The distribution of delta18O and delta13C in the surface and LGM samples are strikingly similar, indicating that the impact of SST and SSS has been maintained, and nutrient inputs, mainly from the northeastern and southwestern ends, have been controlled by monsoons since the LGM. Comparisons of the modern and LGM delta18O indicate a difference of about 3.6 °C in bottom-water temperature and a large surface-to-bottom temperature gradient during the LGM as compared to today.

Particle flux studies of sediment traps from the northern and equatorial Indian Ocean

The Asian monsoon system governs seasonality and fundamental environmental characteristics in the study area from which two distinct peculiarities are most notable: upwelling and convective mixing in the Arabian Sea and low surface salinity and stratification in the Bay of Bengal due to high riverine input and monsoonal precipitation. The respective oceanography sets the framework for nutrient availability and productivity. Upwelling ensures high nitrate concentration with temporal/spatial Si limitation; freshwater-induced stratification leads to reduced nitrogen input from the subsurface but Si enrichment in surface waters. Ultimately, both environments support high abundance of diatoms, which play a central role in the export of organic matter. It is speculated that, additional to eddy pumping, nitrogen fixation is a source of N in stratified waters and contributes to the low-d15N signal in sinking particles formed under riverine impact. Organic carbon fluxes are best correlated to opal but not to carbonate, which is explained by low foraminiferal carbonate fluxes within the river-impacted systems. This observation points to the necessity of differentiating between carbonate sources for carbon flux modeling. As evident from a compilation of previously published and new data on labile organic matter composition (amino acids and carbohydrates), organic matter fluxes are mainly driven by direct input from marine production, except the site off Pakistan where sedimentary input of (marine) organic matter is dominant during the NE monsoon. The explanation of apparently different organic carbon export efficiency calls for further investigations of, for example, food web structure and water column processes.

Planktic foraminifera from ODP Hole 117-723B

Upwelling occurs during the summer off the coast of Oman when the Asian monsoon produces strong southwest winds in the northern Arabian Sea. Ekman transport driven by the southwest monsoon winds upwells cool nutrient-rich waters along the coast which contrast with the warmer, less productive waters offshore. The spatial pattern of foraminifers in the sediments corresponds with the coastal environmental gradient. The upwelling species Globigerina bulloides dominates the sediment assemblage on the continental margin, while Globigerinita glutinata is more abundant offshore, creating a coastal gradient in fauna. We reconstructed the upwelling faunal gradient using high resolution oxygen isotope stratigraphy to correlate between Hole 723B on the Oman Margin, and a core from the Owen Ridge (RC2761), adjacent Site 722. A gradient similar in magnitude to the present, implying upwelling conditions similar to today existed during each interglacial time during the late Pleistocene interval from 0 to 300 k.y. The gradient was reduced or absent during glacial times implying diminshed southwest winds along the coast of Oman, not strong enough to produce an environmental gradient between the coast and offshore sites.

Early - Late Miocene palaeoclimate data and palaefloras of 48 samples from Southern China

Southern China, especially Yunnan, has undergone high tectonic activity caused by the uplift of Himalayan Mountains during the Neogene, which led to a fast changing palaeogeography. Previous study shows that Southern China has been influenced by the Asian Monsoon since at least the Early Miocene. However, it is yet not well understood how intense the Miocene monsoon system was. In the present study, 63 fossil floras of 16 localities from Southern China are compiled and evaluated for obtaining available information concerning floristic composition, stratigraphic age, sedimentology, etc. Based on such reliable information, selected mega- and micro-floras have been analysed with the coexistence approach to obtain quantitative palaeoclimate data. Visualization of climate results in maps shows a distinct spatial differentiation in Southern China during the Miocene. Higher seasonalities of temperature and precipitation occur in the north and south parts of Southern China, respectively. During the Miocene, most regions of Southern China and Europe were both warm and humid. Central Eurasia was likely to be an arid center, which gradually spread westward and eastward. Our data provide information about Miocene climate patterns in Southern China and about the evolution of these patterns throughout the Miocene, and is also crucial to unravel and understand the climatic signals of global cooling and tectonic uplift.

Chronology and stable carbon isotopic ratios of sediments from the Western Pacific Warm Pool region

Instrumental data suggest that major shifts in tropical Pacific atmospheric dynamics and hydrology have occurred within the past century, potentially in response to anthropogenic warming. To better understand these trends, we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes (DDwax) in marine sediments from southwest Sulawesi, Indonesia, to compile a detailed reconstruction of central Indo-Pacific Warm Pool (IPWP) hydrologic variability spanning most of the last two millennia. Our paleodata are highly correlated with a monsoon reconstruction from Southeast Asia, indicating that intervals of strong East Asian summer monsoon (EASM) activity are associated with a weaker Indonesian monsoon (IM). Furthermore, the centennial-scale oscillations in our data follow known changes in Northern Hemisphere climate (e.g., the Little Ice Age and Medieval Warm Period) implying a dynamic link between Northern Hemisphere temperatures and IPWP hydrology. The inverse relationship between the EASM and IM suggests that migrations of the Intertropical Convergence Zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the IPWP throughout most of the past two millennia.