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To constrain models on global sea-level change regional proxy data on coastal change are indispensable. Here, we reconstruct the Holocene sea-level history of the northernmost China Sea shelf. This region is of great interest owing to its apparent far-field position during the late Quaternary, its broad shelf and its enormous sediment load supplied by the Yellow River. This study generated 25 sea-level index points for the central Bohai coastal plain through the study of 15 sediment cores and their sedimentary facies, foraminiferal assemblages and radiocarbon dating the basal peat. The observational data were compared with sea-level predictions obtained from global glacio-isostatic adjustment (GIA) models and with published sea-level data from Sunda shelf, Tahiti and Barbados. Our observational data indicate a phase of rapid sea-level rise from c. -17 to -4 m between c. 10 and 5 ka with a peak rise of 6.4 mm a -1 during 8.7 to 7.5 ka and slower rise of 1.9 mm a -1 during 7.5 to 5.3 ka followed by a phase of slow rise from 5 to 2 ka (∼0.4 mm a -1 from -3.58 m at 5.3 ka cal BP to -2.15 m at 2.3 ka cal BP). The comparison with the sea-level predictions for the study area and the published sea-level data is insightful: in the early Holocene, Bohai Bay's sea-level rise is dominated by a combination of the eustatic and the water load components causing the levering of the broad shelf. In the mid to late Holocene the rise is dominated by a combination of tectonic subsidence and fluvial sediment load, which masks the mid-Holocene highstand recorded elsewhere in the region. [ABSTRACT FROM AUTHOR]

The coastal deltaic plain of the Yangtze River between Taihu (Lake Tai) and Shanghai in eastern China has been the scene of human settlement and agriculture since the early Neolithic, becoming increasingly intensive in the Upper Holocene when delta accretion and the establishment of a stable hydrological regime of freshwater lakes and wetlands allowed the development of extensive agriculture and complex society in late prehistoric and dynastic times. During this period the area was significantly affected by changes in sea level, climate and vegetation, resulting in a dynamic and complex environmental history, however little research has concentrated on environmental change and human impacts during the last few millennia. This study focuses on this late period, presenting the results of integrated sedimentary, microfossil and radiocarbon analyses from a core near the eastern margin of Lake Dianshan, to the east of Taihu. After the withdrawal of intertidal conditions and the conversion to freshwater lake at the core site about 2600 cal. yr BP, pollen and algal spore data show that increased sedimentation gradually reduced freshwater depth until a surface peat formed ca. 1500 cal. yr BP. This also dates the start of a switch in woodlands from sub-tropical and warm temperate trees to a mainly cool temperate and coniferous tree flora, under climatic cooling and human impact. After this time water depths at the site increased greatly, partly due to climate change and flooding, but also because of the establishment of deepwater 'paddy' agriculture. Microcharcoal and pollen data show that a major episode of human impact using fire, with deforestation and rice cultivation, occurred between ca. 1500 and 1200 cal. yr BP. These dates suggest it is one of the latest examples of 'flooded-field' 'paddy' cultivation before more intensive agricultural techniques were adopted in the area after ca. 800 cal. yr BP. • We investigate environmental change during the last two and a half millennia at Lake Dianshan in the Yangtze coastal lowlands • Pollen, non-pollen palynomorphs, microcharcoal and AMS radiocarbon analyses are used • After withdrawal of estuarine conditions freshwater wetlands of varying type became established • From about 1500 cal. yr B.P. sub-tropical and warm temperate woodlands were replaced by mainly cool temperate and coniferous trees • From about 1500 cal. yr B.P. sub-tropical and warm temperate woodlands were replaced by cool temperate and coniferous trees [ABSTRACT FROM AUTHOR]

Abstract This study has reconstructed the Holocene relative sea-level history in the relatively tectonically stable Malay Peninsula with two specific objectives: quantifying the sea-level indicative meanings of mangrove sediments and producing new high-quality sea-level index points. In this study, a wetland on the east coast of the Peninsula was extensively surveyed; the elevational relationship between habitat zones and their pollen and diatom assemblages was established; and a number of indicative meanings were precisely quantified for this wetland. This quantified relationship is extrapolated to other coastal sites of the Peninsula for re-calibration of previously published mangrove-based sea-level data. The reconstructed sea-level history from the new and re-calibrated data demonstrates a period of rapid sea-level rise at a rate of 15.8 ± 3.9 mm/a between 10,500 cal a BP at −35.0 ± 4.3 m and 9000 cal a BP at −14.2 ± 1.6 m. The rate of rising sea level was gradually reduced to zero from 9000 to 5000 cal a BP, and by the end of this period the relative sea level reached a highstand of c. 3.3 ± 0.2 m. Over the past 5000 years relative sea level fell to its lowest point at −0.6 ± 0.1 m by 800 cal a BP. This far-field sea-level history has been driven by the global ice-volume change and glacial isostatic adjustment, and it matches well with the modelled ice-volume equivalent sea level. Highlights • Indicative meanings for sea-level index points from mangrove wetland habitats of Peninsular Malaysia are quantified. • A set of high-quality sea-level index points is generated from a coastal site on the east coast of Peninsular Malaysia. • Previously published, mangrove-based, sea-level index points from Peninsular Malaysia are re-calibrated. • The relative sea level in this far-field location felt below the present mean sea level during the late Holocene. • The Holocene RSL history, GIA and ESL in this location are discussed. [ABSTRACT FROM AUTHOR]

Highlights • The Holocene sedimentary history from a non-deltaic coastal site was reconstructed. • The history reveals continuous vertical sedimentary accretion throughout the Holocene. • The rapid early-Holocene sedimentation was a result of RSL rise and strong monsoon. • The mid-late Holocene sedimentation rate was gradully decreased. Abstract This study has examined how the sedimentary processes in the prevalent non-deltaic coastal marine environments along the southeast coast of China have responded to sea-level change and other environmental drivers during the Holocene. Three sediment cores collected from a shallow marine embayment of the Lantau Island, Hong Kong, on the northern coast of the South China Sea, were analyzed. The results of particle size, total organic carbon content, organic carbon and nitrogen ratios, organic carbon stable isotope ratios, abundance of alkenones and radiocarbon dating of these cores have helped reconstruct the sedimentary history of this site. This history shares the similarity in sedimentary processes within the deltaic environment for the early Holocene, because palaeo-incised channels exist in both environments. The first 1500 years of deposition involved rapid channel infill caused by the rapidly rising sea level and strong monsoon-driven discharge. This was followed by a period of decelerated sedimentation under strong marine influence as the sea flooded the wide accommodation space in the subsequent two millennia. Major differences between the two environmental settings occur in the past 7000 years: vertical accretion was seen in the non-deltaic coastal environment, whilst lateral shoreline advance was the dominant process in the deltaic basin. The progressively slowing down in sedimentation rate in the non-deltaic site during the middle and late Holocene was caused by the reduced monsoon discharge, intensified disturbance from tropical cyclone activity and coastal currents. [ABSTRACT FROM AUTHOR]

This study has collected and analyzed seven sediment cores from the Pearl River delta, from which 16 new and high-quality sea-level index points are generated using a new approach. This study has also re-checked and re-calibrated the previously published sea-level data from China's southeast coast with corrections made for tectonic subsidence and sediment compaction factors. These sea-level data indicate a rise of relative sea level from −49.3 ± 0.8 m to the present height between 10,500 and 7000 cal. a BP. This sea-level history is similar to those recorded from other far-field locations and ice-volume equivalent sea-level models. The early to early-middle Holocene sea-level history in the study area shows a phase of accelerated rise at a rate increasing rapidly from 16.4 ± 6.1 mm/a at 10,500 cal. a BP to 33.0 ± 7.1 mm/a at 9500 cal. a BP. This phase was followed by a period of rapid decrease in the rate of sea-level rise to 8.8 ± 1.9 mm/a at 8500 cal. a BP and 1.7 ± 1.3 mm/a at 7500 cal. a BP. During the past 7000 years, the relative sea level in the study area changed very little. This new and complete history of Holocene sea-level change supports the following findings: (1) no obvious higher-than-present sea-level highstand in the Holocene is found from the northern South China Sea; (2) certain proportion of the effects of the predicted glacial isostatic adjustment were cancelled out by the effects of the weak upper mantle viscosity in the study area; (3) meltwater pulse 1b likely exists spanning into the early Holocene; (4) there are significant misfit between sea-level data and glacial isostatic adjustment models, and a revision to the existing ice melting history for the early Holocene is possibly needed. [ABSTRACT FROM AUTHOR]

In order to reconstruct the environmental and climatic conditions of the last and present interglacials, this study has examined a 52 m-long core obtained from a coastal embayment (Chang-Le) on the west coast of Taiwan Strait. The analyses of particle size distributions, total carbon content, organic carbon isotope ratios, n -alkane indices and alkenones from the core reveal two periods of marine transgression. Together with the radiocarbon and optically simulated luminescence dating analyses, the environmental proxies indicate that the older marine sequence (M1) was deposited during the period of rising sea level in the early-to-middle part of MIS5e. The younger marine sequence (M2) was confirmed as a deposit formed during the stable sea level of the latter part of the present interglacial. The shallow marine facies and the abundant alkenones from M2 suggest a deeper water environment under full marine conditions during the last interglacial. The sub-tidal to intertidal facies and weak appearance of alkenones in M1 imply a shallow water environment under weak marine influence. Because the site was close to upland landscape, high input of terrigenous material for both periods is evident. The alkenone-based sea surface temperature (SST) reconstructions indicate that the SST during MIS5e fluctuated slightly around 28.1 °C, which is about one degree higher than that of MIS1, consistent with records from the northern coast of the South China Sea. The depositional conditions and the burial depths of the two marine sequences also provide hints for the local tectonic movements. [ABSTRACT FROM AUTHOR]

In order to reconstruct the Holocene environmental history of a coastal site in the northern South China Sea, this study analysed the organic carbon isotope ratios (δ 13 C org ) and alkenone unsaturation ratios (U K′ 37 ) from a 36.5 m-long sediment core drilled at seabed in the mouth region of the Pearl River estuary and generated a coupled hydrological and temperature record. This record reveals changes of monsoon-induced sediment discharge and sea surface temperature of the Holocene in four stages. In Stage I, the site was under fluvial conditions prior to postglacial marine transgression. Stage II saw an increase of sea surface temperature from c. 23.0 °C to 27.0 °C, associated with a strengthened summer monsoon from c. 10,350 to 8900 cal. years BP. This was also a period of rapid sea-level rise and marine transgression, during which the sea inundated the palaeo-incised channel, i.e. the lower part of the T-shape accommodation space created by the rising sea. In these 1500 years, fluvial discharge was strong and concentrated within the channel, and the high sedimentation rate (11.8 mm/year) was very close to the rate of sea-level rise. In the subsequent 2000 years (Stage III) sea level continued to rise and the sea flooded the broad seabed above the palaeo-incised channel, resulted in fluvial discharge spreading thinly across the wide accommodation space and a much reduced sedimentation rate (1.8 mm/year). Sea surface temperature in this stage reached 27.3 °C initially, but dropped sharply to 26.1 °C towards c. 8200 cal. years BP. The final stage covers the last 7000 years, and the site was under a stable sea level. Sedimentation in this stage varied a little, but averaged at 1.8 mm/year. Whilst fluvial discharge and sea surface temperature didn’t change much, two short periods of hydrological and temperature change were observed, which are related to the climatic cooling events of c. 4200 cal. years ago and the Little Ice Age. [ABSTRACT FROM AUTHOR]

This study has examined bulk and compound specific organic carbon isotopes (δ 13 C org ) and lipid n -alkanes of modern plants and a wetland sediment sequence from the central Tibetan Plateau and explores the usefulness of these two methods for palaeoenvironmental reconstructions. Results show that a combination of δ 13 C org values and n -alkane indices can help differentiate organic matter from C3 terrestrial plant, C4 terrestrial plant and submerged macrophytes, the three main sources of organic matter in the study area. The analyses of total organic carbon, δ 13 C org values and n -alkane indices for the sediment sequence imply that a wetland habitat was established about 8000 years ago, and the wetland conditions were largely stable with dominantly C3 wetland herbs covering the wetland. However, small fluctuations in the dominant organic matter supply between vascular and aquatic plants are revealed, suggesting short duration changes in the extent of open water area within the wetland or variations in the productivity of submerged macrophytes and aquatic plants within the wetland ecosystem, which reflects variations in the strength of precipitation and evaporation. [ABSTRACT FROM AUTHOR]

Paired high-resolution sea surface temperature (SST) records, based on the long-chain alkenone unsaturation index ( U 37 K ′ ) , were reconstructed to decipher the SST evolution over the past 8000 years and its possible driving mechanisms at the Hong Kong coastal region. The two SST records, derived from a sediment core in the Pearl River Estuary and an offshore core in the northern South China Sea (SCS), show different patterns of SST changes. The coastal record shows relatively stable, warm temperatures during the mid-Holocene (∼7.4–2.6 ka), and substantial cooling (>2 °C) thereafter. The cooling was most pronounced in the past ∼0.6 ka, likely associated with the Little Ice Age (LIA). The offshore record generally reveals a warming trend from 8 ka to ∼3.5 ka and relatively warm temperatures since then. As a result, the SST difference (ΔSST) between the two sites increased over time, suggesting that the SST gradient gradually developed in the northern SCS. The declining coastal SST with the increasing ΔSST likely indicates and results from the intensified East Asian winter monsoon since ∼7 ka, especially during the late Holocene. Consistent with previous terrestrial records revealing winter monsoon variability and modern observations, ΔSST between coastal and offshore sites could thus be used as an indicator of winter monsoon variability. [ABSTRACT FROM AUTHOR]

Abstract: This study examines n-alkane distributions from a 120 m long borehole extracted from Palaeolake Tianyang, South China, which covers the last five glacial cycles. We aim to determine the palaeoclimatic/environmental fidelity of n-alkane distributions in bulk organic matter (OM) from this tropical sedimentary archive. The Tianyang lithostratigraphy reveals a deep-lake sequence (120–42 m) dominated by diatomite, overlain by shallow-lake and marsh sediments in the upper 42 m. The Carbon Preference Index (CPI, C23–C31) suggests that there is weak odd/even predominance (OEP) in long chain n-alkane distributions (C27–C31) in OM from deep lake sediments, and a strong OEP of long chain n-alkane distributions in OM from shallow lake sediments. The opposite characteristics are evident in short chain n-alkane distributions (C16–C20). These CPI values suggest different sources of organic carbon within the deep (dominantly diatom synthesis) and shallow lake (dominantly high plant input), but cannot help differentiate glacial from interglacial sediments. The Terrigenous-to-Aquatic Ratio (TAR) shows high values throughout interglacial sediments (>4) and low values in glacial sediments (<4), corresponding to a higher productivity of high plants during interglacials, and vice versa. The proportion of aquatic plant n-alkanes (P aq) also reveals a clear change between glacial (0.31–0.39) and interglacial periods (0.22–0.28) during shallow lake stage, indicating a reduction in terrestrial OM input during glacial periods relative to interglacial periods. There is a greater amount of Unresolved Complex Mixture (UCM) in glacial sediments than within interglacial sediments. We suggest that the above n-alkanes indexes are useful environmental/climatic indicators within Palaeolake Tianyang, despite the fact that some other indexes, like Average Chain Length (ACL), provide less definitive interpretations. [Copyright &y& Elsevier]

Abstract: A 9500-year Holocene pollen record from a river valley wetland of the central Tibetan Plateau reveals the history of climate fluctuations. At the beginning of the Holocene, the catchment area of the study site was covered by sparse drought-tolerant herbaceous vegetation, suggesting a climate cooler and drier than today. This period was characterised by a high rate of soil erosion as indicated by the deposition of siliciclastic sediment at the site. The environment became wetter during the early mid-Holocene around 8060–7120 cal. BP, and during which a wetland habitat dominated by sedges was developed at the site. Throughout the mid-Holocene, the wetland remained stable, with steady accumulation of organic material. A change to a slightly drier condition took place in the late Holocene, and after about 1000 cal. BP, a marked increase in drought-tolerant herbs occurred. Although no trees lived around the site, the record shows low, but steady increasing, tree pollen frequencies throughout the mid-late Holocene. This result confirms a stable, largely monsoonal, climate in central Tibet over the middle to late Holocene. It also suggests that the optimum period of monsoonal precipitation in central Tibet occurred later and lasted longer than that in the East Asian Monsoon region. [Copyright &y& Elsevier]

Abstract: Expansion or shrinkage of closed lakes is a natural response to fluctuations in precipitation and evaporation, linked closely to changes in strength or position of atmospheric circulation. In Tibet, there are many such lakes with paleo-shorelines that can be used for reconstructions of climate history. Despite the fact that many paleo-shorelines are well preserved in Tibet, dating them has been seriously hindered by various difficulties. Here we present the first optical dating chronology for a series of paleo-shorelines in Zhari Namco, the third-largest inland lake in central Tibet. Our results indicate that the lake level has dropped 128m over the past 8.2ka. Younger shorelines are found at lower altitudes, indicating that the shorelines follow a geomorphic-chronological order and a broadly continuous trend of stepwise shrinkage. The surface area of Zhari Namco has shrunk in size from 4605km2 at 8.2ka ago to 996km2 at present; 300km3 of water has been lost from this lake. Such a loss in water implies a significant reduction in precipitation over the past 8.2ka, a likely result of a weakening Asian monsoon. Following the decreasing precipitation since the early Holocene, this area has become increasingly arid. [Copyright &y& Elsevier]

Abstract: Environmental change plays a significant role in the development of agriculture worldwide. The availability of wetland habitats and freshwater supply has been particularly important to the expansion and sustainability of rice-based economies. Some studies have emphasized the connections between societal changes and climatic fluctuations. However, recently emerged evidence has indicated the prevalence of human's initiatives. To tackle this complex issue, we employ a multi-proxy approach applying microfossil diatom/pollen and organic carbon isotopes collected from sediment cores of multiple locations to the reconstructions of palaeo-environment and identification of agricultural activity in the northern part of the Pearl River delta. Our study confirms the importance of environmental conditions, but also reveals initiatives taken by the agricultural communities in site selection for cultivation and settlements. Our results also show that freshwater wetland conditions became available in the most landward part of the deltaic plain along the West/North Rivers as early as 7000 years ago, since which wetland habitats expanded seawards as the deltaic shoreline advanced. By 2500 years ago, extensive freshwater wetlands already emerged in northwest part of the deltaic plain. However, before this time, economic activity within the deltaic basin was still predominantly based on fishing and gathering. This is possibly because the Neolithic communities did not need to adapt the labour-intensive cultivation due to the abundance of natural resources in the deltaic region, a strong contrast to what the communities in the Yangtze valley did 5000 years earlier. The agriculture was finally expanded about 2500–2200 years ago in a small area of marsh wetlands along a small river on the northern edge of the deltaic plain by a community migrated from the Yangtze basin. The agricultural activity was spread across the deltaic plain by about 1000 years ago, again as a result of the influx of migrants from the Yangtze basin. This study highlights the usefulness of the multi-proxy, multiple location approach that has helped pin-pointing the location where agriculture in the study area was originated. [Copyright &y& Elsevier]

Abstract: The early Holocene history of the Pearl River delta is reconstructed based on a series of sediment cores obtained from one of the main palaeo-valleys in the basin. Sedimentary and microfossil diatom analyses combined with radiocarbon dating provide new evidence for the interactions between sea-level rise, antecedent topography and sedimentary discharge changes within the deltaic basin since the last glacial. These new records show that river channels of last glacial age incised down to c. −40 m into an older (possibly MIS5 age) marine sequence which forms the floor of the deltaic basin and exists primarily at c. 10 m–15 m below present mean sea level. Rapid postglacial sea-level rise flooded the incised valleys by the beginning of the Holocene, and prior to c. 9000 cal. years BP, marine inundation was largely confined within these incised valleys. The confined available accommodation space of the incised valleys combined with strong monsoon-driven freshwater, high sediment discharge and a period of rapid rising sea level meant that sedimentation rates were exceptionally high. Towards c. 8000 cal. years BP as sea level rose to about −5 m, marine inundation spilled out of the incised valleys and the sea flooded the whole deltaic basin. As a result, the mouth of the Pearl River was forced to retreat to the apex of the deltaic basin, water salinity within the basin increased markedly as the previously confined system dispersed across the basin, and the sedimentation changed from fluvial dominated to tidal dominated. Sea level continued to rise, albeit at a much reduced rate between 8000 and 7000 cal. years BP, and deltaic sedimentation was concentrated around the apex area of the basin. During the last 7000 cal. years BP, the delta shoreline moved seawards, and the sedimentary processes changed gradually from tidal dominated to fluvial dominated. [Copyright &y& Elsevier]

Understanding the mid-Holocene dynamics of the East Asian monsoon (EAM) is integral to improving models of the Holocene development of the global climate system. Here we reconstruct the mid-Holocene EAM history from the Pearl River estuary, southern China, using bulk organic carbon isotopes (δ13C), total carbon to total nitrogen (C/N) ratios and total organic carbon (TOC) concentration. Sedimentary δ13C, C/N and TOC are potentially good indicators of changes in monsoonal precipitation strength. Sediments buried during a period of high precipitation exhibit a high proportion of terrigenous material, and have low δ13C and high C/N, and vice versa during a period of low precipitation. Results suggest a general decreasing trend in monsoonal precipitation from 6650 to 2150 cal. yr BP because of the weakening Northern Hemisphere insolation most likely related to the current precession circle. Superimposed on this trend are apparent dry–wet oscillations at centennial to millennial timescales most likely in response to solar activity. Mismatches between our δ13C record and results from the Dongge Cave in southern China at millennial timescales may indicate that the δ13C from the Pearl River estuary reveals changes in precipitation over a broader area than the δ18O from Dongge Cave. [ABSTRACT FROM AUTHOR]

Abstract: During the mid-Holocene the eastern Taihu area, on China''s Yangtze delta plain, was populated by advanced late Neolithic cultures supported by intensive domesticated rice cultivation. This agricultural system collapsed around 4200cal yr BP, with severe population decline, the end of the Liangzhu culture, and about half a millennium of very low-scale human activity in the area before the re-establishment of agricultural production. Microfossil analyses from six sedimentary sequences, supported by AMS 14C dating, has allowed reconstruction of mid-Holocene hydrological conditions and salinity changes which would have had a major influence on agricultural viability and cultural history in the coastal wetlands. These data, allied to existing stratigraphic and sea-level records, show that chenier ridges that developed after ca. 7000cal yr BP in the east of the area sheltered it from marine inundation and, although still connected to the sea through tidal creeks, low-salinity conditions persisted throughout the Neolithic period. There is no evidence that marine flooding caused the collapse of Liangzhu culture. Marine influence was stable and evolved slowly. Social and cultural causes may also have been important, but if environmental change triggered the collapse of Neolithic agricultural society here, other natural forces must be sought to explain this event. [Copyright &y& Elsevier]

Abstract: Preservation of organic matter in estuarine and coastal areas is an important process in the global carbon cycle. This paper presents bulk δ13C and C/N of organic matter from source to sink in the Pearl River catchment, delta and estuary, and discusses the applicability of δ13C and C/N as indicators for sources of organic matter in deltaic and estuarine sediments. In addition to the 91 surface sediment samples, other materials collected in this study cover the main sources of organic material to estuarine sediment. These are: terrestrial organic matter (TOM), including plants and soil samples from the catchment; estuarine and marine suspended particulate organic carbon (POC) from both summer and winter. Results show that the average δ13C of estuarine surface sediment increases from −25.0 ± 1.3‰ in the freshwater environment to −21.0 ± 0.2‰ in the marine environment, with C/N decreasing from 15.2 ± 3.3 to 6.8 ± 0.2. In the source areas, C3 plants have lower δ13C than C4 plants (−29.0 ± 1.8‰ and −13.1 ± 0.5‰ respectively). δ13C increases from −28.3 ± 0.8‰ in the forest soil to around −24.1‰ in both riverbank soil and mangrove soil due to increasing proportion of C4 grasses. The δ13CPOC increases from −27.6 ± 0.8‰ in the freshwater areas to −22.4 ± 0.5‰ in the marine-brackish-water areas in winter, and ranges between −24.0‰ in freshwater areas and −25.4‰ in brackish-water areas in summer. Comparison of the δ13C and C/N between the sources and sink indicates a weakening TOM and freshwater POC input in the surface sedimentary organic matter seawards, and a strengthening contribution from the marine organic matter. Thus we suggest that bulk organic δ13C and C/N analysis can be used to indicate sources of sedimentary organic matter in estuarine environments. Organic carbon in surface sediments derived from anthropogenic sources such as human waste and organic pollutants from industrial and agricultural activities accounts for less than 10% of the total organic carbon (TOC). Although results also indicate elevated δ13C of sedimentary organic matter due to some agricultural products such as sugarcane, C3 plants are still the dominant vegetation type in this area, and the bulk organic δ13C and C/N is still an effective indicator for sources of organic matter in estuarine sediments. [Copyright &y& Elsevier]

Abstract: We collected 77 modern diatom samples from sites across the Pearl River estuary, China to analyze the relationship between diatom assemblages and environmental parameters including water salinity, water depth and sediment particle size. Results showed that marine diatoms were dominant in the high salinity environment around Hong Kong and the outer part of the estuary. Brackish water diatoms were found in high abundance in the central part of the estuary. Both marine and brackish water diatoms were predominantly planktonic taxa. Freshwater diatoms dominated in low salinity environments, with planktonic taxa in the deep tidal channel and benthic species in the shallow deltaic distributaries. Statistical tests indicated that the modern diatom distribution is strongly correlated with salinity but is also influenced by several other environmental variables including sand content and water depth. Transfer functions relating diatom assemblages and water salinity had high r 2 (0.94–0.98 for WA-PLS, 0.95 for MA and 0.98 for MAT) and relatively low RMSEP (2.66–1.63‰ for WA-PLS, 2.35‰ for MA and 2.70‰ for MAT). Due to the geographical distribution of samples, some spatial autocorrelation is likely present in the dataset. When this effect is considered, r 2 decreases to 0.90 and RMSEP increases to 5.41‰, although the diatom–salinity relationship remains appropriate for reconstructing paleosalinity. Based on this estimate, a diatom-based salinity transfer function with high accuracy and precision is developed and successfully applied to a sediment core for quantitative reconstruction of the Holocene paleosalinity in the Pearl River estuary. [Copyright &y& Elsevier]

Abstract: The date and location of the adoption of rice cultivation by foraging cultures in China are of considerable current interest but its understanding is hampered by lack of information regarding its palaeoenvironmental context. We present detailed multi-proxy palaeoecological research at the earliest-dated site of rice cultivation in the coastal littoral of east China which has revealed the precise environmental setting of this early Neolithic settlement and its incipient cultivation at ca 7750calBP. Regional and local environmental changes governed the character of the site and the duration of human activity. After an episode of marine conditions, natural hydrological succession and terrestrialisation of the site preceded fire clearance of marsh fen-carr alder scrub that prepared the ground for cultivation and then maintained a reedswamp-type wet grassland in which rice was grown. Cropping of Typha stands may have formed part of the subsistence base before the site was overwhelmed by marine inundation ca 7200calBP, after which rice cultivation spread to Neolithic sites of Hemudu type elsewhere in the coastal lowlands. We suggest that integrated multi-proxy palaeoecological studies are vitally important for the full understanding of such key wetland archaeological sites. [Copyright &y& Elsevier]

Abstract: Archaeological records of the Neolithic settlements on the eastern China coast between 35°N and 30°N, an area covering the abandoned Yellow River and the Yangtze River delta plains, reveal that Neolithic people moved from the Yellow River basin onto the northern coast for fishing, hunting and dry-land agriculture ~7000 yr ago. Marine transgression interrupted their activities on the low-lying (2–5 m in elevation) coastal wetlands between 6000 and 5000 yr ago, after which they reclaimed their land near the river mouths. Their migration routes on the southern Yangtze delta plain indicate another scenario: early Neolithic communities moved onto the plain for wet-rice cultivation. Despite relative sea-level rise from 7000 to 4000 yr ago, a large number of settlements were established on the lowlands between the eastern Chenier Ridges and the western Taihu Lake depression. The Chenier Ridges, with ~1.0 m higher topography than the adjacent coastal area, played a role in sheltering the Neolithic people. Subsequently, settlements waned considerably, possibly due to further marine inundation combined with cold climate. The present study shows that migration patterns of the Neolithic settlements are closely associated with a gradually rising sea level between 7000 and 4000 yr ago. [Copyright &y& Elsevier]

Abstract: We collected modern diatom samples from two mangrove environments of Sulawesi, Indonesia to provide a much needed dataset for the reconstruction of sea level from tropical environments. The diatom assemblages are dominated by mesohalobous species (e.g. Amphora coffeaeformis, Amphora turgida, Achnanthes delicatula, Nitzschia sigma and Tryblionella balatonis) and oligohalobous (e.g. Amphora veneta, Diploneis ovalis and Progonoia didiomatia) taxa. Both study sites show strong vertical zonations, which suggests that duration and frequency of intertidal exposure are important factors in controlling the relative abundance of diatoms. The assemblages can be generally divided into a mixed assemblage of mesohalobous, oligohalobous–halophilous and oligohalobous-indifferent diatoms that are found from the dense mangrove vegetation towards the landward edge of the transects, and mesohalobous diatom assemblages that are located within the fringing Rhizophora and tidal flat environments. We subsequently developed a diatom-based transfer function, which is a quantitative approach to sea-level reconstruction. The relationship between observed and diatom-predicted elevations suggests accurate and precise reconstructions are possible. The error estimate (±0.15 m) is comparable to diatom-based transfer functions from temperate marshes. [Copyright &y& Elsevier]

Various sea-level curves have been proposed for the coast of China in the past two decades. These sea-level curves indicate a complex history of Holocene sea level, and so the debate on whether or not a higher mid-Holocene sea-level highstand exists in the coast of China has continued. This paper aims to re-examine the Holocene sea-level history for the low latitude part of the China coast (between 18°N and 32°N) by re-assessing all the sea-level data available from the east to south coasts and separating them according to geological settings in order to examine the influences of global and local factors. The reconstructed sea-level histories from different coastal sectors of the China coast reveal a certain degree of variability in the timing and height of mid-Holocene sea-level highstand. Within large river deltas, the mid-Holocene sea-level highstand occurred earlier by almost 1000 years than that from other coastal sites. The highstand from large river deltas appears also lower in altitude (a few metres below the present-day sea level) due probably to the local factors of subsidence and sediment consolidation. In geologically stable coastal sites, the highstand is recorded at the same altitude as the present-day sea level. A 1–2 m higher highstand is found from sites where tectonic uplift is observed. [Copyright &y& Elsevier]

There are three major typhoon hazards that apply to the Shanghai area. First, gale-force winds can damage buildings and service facilities. The most severe damage from this occurs only when a typhoon strikes Shanghai directly. Second, both the urban and rural sections of Shanghai are liable to flooding during typhoon seasons. These floods occur when typhoon-induced storm surges coincide with high spring tides and meet with high discharges from the river network as a result of the typhoon downpours. Third, typhoon-induced torrential rain has caused waterlog hazards, particularly in the most densely populated parts of Shanghai. The waterlog hazard has been exacerbated by land subsidence and poor management of pumping systems. In order to prevent disasters happening and reduce the scale of damage, the government has issued construction guidelines and invested in flood defences. Further measures are to be brought in including engineering projects, educational programmes and insurance policies. [ABSTRACT FROM AUTHOR]

This study was conducted to (1) investigate a former mangrove wetland on the east coast of Peninsular Malaysia near Kuantan and produce new sea-level index points (SLIP), and to (2) re-analyzed the modern vegetation and pollen results from a mangrove-swamp transect within the nearby estuary to establish the relationship between vegetation zones and tidal levels for estimating indicative meanings (IM) for the SLIPs. The results indicate that the modern floral and pollen zones match well with the fossil ones, and four IMs were appropriately established. Combining with the recently published SLIPs from Terengganu, the 15 new SLIPs from Kuantan were used to reconstruct the middle-to-late Holocene relative sea-level (RSL) history for the east coast of the Malay Peninsula. This history shows that the RSL reached c. 1.5 m msl around 6500 cal. a BP and rose to c. 2.0 m msl by 4500 cal. a BP. This phase of RSL rise in this far-field site supports the hypothesis that additional ice melting occurred between 7000 and 4000 cal. a BP. During this phase of RSL rise, erosion and redeposition of estuarine sediments occurred at the study site. Since 4000 cal. a BP, the RSL fell gradually to below the present height by 800 cal. a BP. In general, this RSL history matches well with the GIA model with the ICE4G melting history. Furthermore, the SLIPs from the east coast are systematically lower in elevation than those recorded in the west coast. The difference is about 1.5 m in the beginning of the middle Holocene and it decreases gradually towards the late Holocene. This difference, thus, implies the existence of continental levering during the Holocene. • Indicative meanings for sea-level index points generated from a modern mangrove transect. • New mangrove-based sea-level index points generated from the east coast of the Malay Peninsula. • RSL reached 1.5 m by 6500 cal. a BP and 2.0 m by 4500 cal. a BP, implying continuous ice melting from 7000 to 4000 cal. a BP. • Relative sea level fell from 4000 cal. a BP to below the present height by c. 800 cal. a BP. • RSL in the early mid-Holocene in the east coast was 1.5 m lower than that in the west coast, implying continental levering. [ABSTRACT FROM AUTHOR]

An important focus in research over the past decade is the relationship between climatic/environmental change and human cultural evolution during the Holocene. This decade saw an increasing number of natural scientists involved in this research, which led to debates and collaborations between natural scientists and archaeologists/anthropologists. This decade also witnessed an increase in multidisciplinary research across these subjects, which has improved significantly the understanding of the human–environment relationship. As part of this research drive, this Special Issue highlights the importance of multidisciplinary studies, mainly from China, on early rice agriculture, impacts of environmental change in Neolithic communities, and new approaches for environmental reconstruction. [ABSTRACT FROM AUTHOR]

In order to examine the role of human drivers in shoreline advance of the Pearl River delta plain over the past 7500 years, this study reconstructed several palaeo-shorelines based on sedimentary records, archaeological findings, historical archives, family ancestral books and modern survey data. With these shorelines, this study quantified the land growth rate for each of seven time periods spanning from the Neolithic-Bronze Ages, through the agricultural period, to the modern industrial era. The results show that, since c. 7500 cal. a BP as the sea level ceased to function as the primary driver, fluvial discharge and tide became the main natural drivers. Between 5500 BCE and 200 BCE, as fluvial discharge was progressively reduced, the amount of sediment drained out to the sea by tidal action was also progressively reduced due to the decrease of the estuarine space. As a result, the land growth rate was kept around 0.36–0.38 km2/a for this period. During the agricultural stage between 200 BCE and 1950 CE, human activity has led to a continuous increase of land growth rate, from 0.78 km2/a caused by land clearance (200 BCE to 960 CE) to 2.69 km2/a triggered by early land reclamation (960–1370 CE) and further to 4.50 km2/a as more advanced techniques were used (1370–1950 CE). Finally, a better organization of human power in land reclamation and the use of machinery since 1950 CE has accelerated the land growth to an average of 10.56 km2/a. The river damming and soil preservation projects in the past three decades have greatly reduced sediment supply and caused a significant slowdown in the shoreline advance. • Sixteen deltaic shorelines of the past 7500 years were reconstructed. • Land growth rates of the delta plain were quantified. • The shoreline advance during 5500–200 BCE was dominated by natural drivers. • Human driver accelerated the delta advance during agricultural and industrial eras. • Levee construction and land reclamation played an important role in delta advance. [ABSTRACT FROM AUTHOR]

In order to examine relative sea-level responses to the postglacial ice-volume change and the glacio-hydro isostatic adjustments (GIA), this study investigated the inner part of the Hangzhou Bay, east China, a tectonically relatively stable far-field location, and reconstructed the early to middle Holocene sea-level history. This investigation has established the elevational relationship between modern saltmarsh-mudflat and tidal levels based on diatom analysis for sea-level indicative meaning estimates, produced 17 high-quality sea-level index points, and simulated GIA processes for the study site. These results reveal that the relative sea level rose from −38.3 ± 1.6 m in c. 10,000 cal a BP to the present height by c. 7000 cal. a BP, and the average rate of sea-level rise decreased gradually from 19.6 ± 2.6 mm/a to 2.3 ± 1.5 mm/a during the 3000 years. This period of sea-level history was punctuated by two episodes of accelerated rise around 8200 and 7500 cal a BP. The relative sea level rose to 0.8 ± 1.4 m above msl by c. 6500 cal. a BP, followed by a gradual fall back to the present height at 4500 cal a BP, implying a different response to the potential additional ice melting between 7000 and 4000 cal a BP. A comparison of the sea-level histories between the inner and outer Hangzhou Bay indicates the coastal levering effect due to the marine inundation of the continental shelves. A further comparison between sea-level data from China and Malay Peninsula reveals different GIA effects between the Cathaysia-Yangtze Blocks and the Sundaland Block. • A modern analogue between diatom zones and tide levels. • RSL rose from −38.3 ± 1.6 m in 10,000 cal a BP to present height by 7000 cal a BP. • Punctuated by two episodes of accelerated rise around 8200 and 7500 cal a BP. • Evidence of coastal levering during the early Holocene. • Different GIA responses of Cathaysia Block and Sundaland Block to IESL. [ABSTRACT FROM AUTHOR]

The peak period of marine isotope stage 5 (MIS5e) is the most recent warm period largely comparable to the present interglacial, marine isotope stage 1 (MIS1). The spatial variations in sea surface temperature (SST) between MIS5e and MIS1 can reveal the important differences in the effects of insolation and oceanographic conditions between the two warm periods, which in turns help refine global climate models. In order to quantify the differences, this study calculated the SST for the peak periods of MIS5e (c. 128-113 ka BP) and MIS1 (c. 8-3 ka BP) along the low-latitude western North Pacific margin (18 oN to 26 oN). Together with the previously published data from the South China Sea (9 oN to 19 oN), the results indicate a generally northwards decreasing trend in the two interglacial periods. This latitudinal SST trend in both peak MIS 1 and MIS 5e can be attributed to the strong influence of ocean currents in the studied region. Secondly, the average SST of peak MIS5e is 1.3 ± 0.2 °C higher than that of peak MIS1, suggesting a higher level of insolation during the previous interglacial. However, the above general pattern is complicated by the near-shore and offshore difference in the effects of winter monsoon on oceanic conditions around 20–22 oN. The coastal upwelling near 26 oN during peak MIS5e reduced the SST, whilst the SST was raised as the upwelling ceased during peak MIS1. Finally, the SSTs of the two warm periods are significantly higher than the present SST from 20 oN northwards, implying the influence of winter monsoon cold current in the Taiwan Strait. • Northward SST decreasing trend might be controlled by ocean current. • ΔSST between peak MIS5e and MIS1 is 1.3 ± 0.2 °C. • Summer insolation may probably influence SST differences between periods. [ABSTRACT FROM AUTHOR]

The article focuses on a study which examined the environmental conditions associated with the rise and fall of the Neolithic culture in the Hangzhou Bay and Taihy areas of China. Results of the study showed that the freshwater salt-tolerant taxa indicate a long period of low salinity conditions during the Middle Holocene. It also found that the Yuanjiadi area was under stable, wetland conditions. Pollen data also showed indications of forest composition in the area.

Reconstructing the Holocene megaflood history is a key component of understanding the mechanism of past climate change and assessing the potential impact of future catastrophic events. The Pearl River is the longest watercourse in southern China, and its lower reach has been identified as one of the world's most vulnerable regions for flood exposure. However, there is a complete lack of millennial-scale geological records of paleomegafloods for the future prediction of once-in-a-hundred (even once-in-a-thousand) year floods in southern China. Here, we identified a series of paleomegaflood deposits interbedded with wood-rich peat layers in the lower West Pearl River area. All paleoflood layers have been well dated using AMS 14C dating method. According to the regional correlation of the flood sequence, sediment characteristics and provenance analysis, there have been at least 7 megafloods corresponding to once-in-a-thousand-year events in the lower reaches of the West Pearl River during the past 6000 years, with an average return period of approximately 855 years. The identified paleomegafloods were coeval with periods of strong El Niño-Southern Oscillation (ENSO), indicating that weakening of the Asian summer monsoon, associated with enhanced ENSO variability, may have triggered abnormally high precipitation leading to flooding of exceptional magnitude in southern China. In addition, the most prominent paleomegafloods identified in the lower Pearl River coincided with intervals of lower precipitation and fewer storms in central-eastern China, indicating the intensification of the meridional "tripole" pattern of precipitation across eastern China during the latter half of the Holocene. Increased land use and deforestation over the last 2000 years have resulted in soil loss and rapid degradation of local primeval forest ecosystems, leading to more catastrophic flooding. Large amounts of rice pollen in the uppermost flood layer during the Song Dynasty indicate that this megaflood may have inundated a large area of cultivated land. The periodic occurrence of Holocene megafloods not only caused damage to human existence, but also affected the evolution of local civilization. This study reveals for the first time a series of Holocene millennial-scale megafloods and sheds new light on the importance of atmosphere-ocean interactions in the tropical Pacific and monsoon subtropical climate dynamics for precipitation anomalies in East Asia. Our data yield valuable information for future research into climate extremes and hazard prevention. [ABSTRACT FROM AUTHOR]

To investigate the relationship between the alkenone unsaturation index (U37K′) and sea surface temperature (SST) in coastal and continental shelf waters, 58 surface sediment samples were collected from the South China Sea (SCS), Taiwan Strait, and East China Sea (ECS). We combined the new results with the previously published 71 data points from the SCS, the shallow water areas of the Yellow Sea (YS) and northern ECS, to form a dataset with sample sites spanning across 6°N and 37°N (including annual SST calibration between 14.3°C and 28.6°C). With this dataset, we examined the U37K′-SST relationship based on 129 samples from the Western North Pacific (WNP) margin as well as using 85 samples from specific WNP shallow water. The U37K′ index from the low-mid latitudinal WNP margin demonstrated a good correlation with the surface annual mean SST (0–50 m water depth; R2=0.89). The slope of linear regression (U37K′-SST) based on the coastal-continental shelf samples with water depth less than 200 m is similar to that of the published global open ocean regression equation. These results confirm that U37K′ can be used as a shallow sea water SST proxy in mid-low latitudes of the WNP marginal seas. In addition, our reintegrated U37K′-SST results based on 172 global shallow water samples are similar (similar slopes and intercepts) to the shallow ocean results in the WNP marginal seas. However, the similarity of the regression formula to the open ocean does not imply that the formula is applicable. For example, of the 85 data in the shallow waters from the marginal sea in this study, the majority of data points lie above the regression line, showing positive residuals for U37K′. This regression bias appears to be caused by specific marine environments, such as warm ocean currents and/or high nutrient conditions that result in positive U37K′ residuals. Taken together, considering the specific temperature and environmental factors in the shallow waters of the low-mid-latitude WNP margin, we propose a nonlinear U37K′-SST regression formula: U37K′ = −1.2488+0.1740×SST−0.0035×(SST)2, R2=0.93, N=85, specifically for the environments with SST below 24°C. [ABSTRACT FROM AUTHOR]

• Reconstructed four mouth bars' (MB) development history of the West Pearl River. • Hydrodynamic conditions in Pearl Delta allow MB to form from 16 m water depth. • Natural vertical MB growth duration varies between 2800 and 2000 years. • Duration is inversely related to natural depositional rate from 2.7 to 5.7 mm/a. • Sediment supply and antecedent landscape are controlling factors. River mouth bars' formation is a key process of the delta development and river bifurcation, but details of the long-term developmental history of mouth bars and their role in the delta evolution are substantially less well documented. To characterize deltaic mouth bars' development, this study investigated the Sixianjiao, Jun'an, Da'aosha and Denglongsha mouth bars formed successively along the main course of the West Pearl River. The detailed lithological analyses of sediment cores indicate that the mouth bar sediment is characterized by its sandy nature with mud laminations or lenses and poorly preserved foraminifera. The onset of mouth bar sedimentation is affected by water depth. The Sixianjiao and Jun'an mouth bars initiated at shallower water depth (8.0 m and 11.0 m, respectively) due to the restrictions of higher basement landforms. In an area where water is deeper, the mouth bar development would begin only with the site being elevated up to about 16.0 m water depth, such as a case in Da'aosha. The duration between their onset and end of vertical growth varies between 2000 and 2800 years, which is inversely related to their sedimentation rates between 2.7 and 5.7 mm/a, indicating the importance of sediment supply. In addition, the locations of the four mouth bars were to some extent determined by the antecedent landscapes. Finally, the ages of these four mouth bars show a chronological order from land to sea, reflecting seaward delta progradation, contrary to previous morpho-dynamical numerical model's predictions. Our reconstruction of the West Pearl River mouth bars' developmental history provides a new insight into the geomorphological evolution of the Pearl River delta, a special delta developed within a complex estuarine bay. [ABSTRACT FROM AUTHOR]

Abstract: Distinguishing between natural and human-induced sources of estuarine sedimentary elemental concentrations often relies on mathematical normalisation (using geochemical or granulometric variables) and multivariate statistical techniques (e.g. Principle Component Analysis (PCA)). However, the extent to which these mathematical treatments can influence the interpretation of the data is not well constrained. We report here the highest resolution mapping of surface sediment elemental concentrations in the Pearl River Estuary (PRE) to date (n = 77) and detail an investigation on the effect of “pre-defining” elements of interest before statistical analysis, a comparison of common normalisation techniques and discuss implications for the identification and interpretation of sediment elemental concentrations enriched by human activities. Our analysis indentifies 4 distinct patterns of distribution in the PRE: North River, Western Shoal, Macau and Coastal Water distribution patterns. Mapping of these raw distribution patterns underpins a conceptual understanding of the interacting processes driving these patterns of deposition in the PRE, aiding the implementation of PCA and mathematical normalisation. However, we find evidence that (i) different normalisation elements/parameters can significantly alter the distribution patterns in elemental concentrations when applied across the entire PRE and may not reflect the true distribution (i.e. an artefact), and (ii) developing a reduced dataset for PCA can also alter the underlying trends in the spatial data; both of which significantly impact upon the subsequent environmental interpretation of source and human-induced pollution effects. However, we demonstrate that through interpolation and mapping of raw geochemical data, zonation of the PRE can allow for much more accurate normalisation within discrete regions using the most appropriate conservative tracer element for each specific region identified. [Copyright &y& Elsevier]

Holocene sea-level rise, monsoonal discharge and human activity have been the main drivers for the evolutionary history of Asian deltas. In theory, when sea level ceased to rise in around 7000 cal. a BP, deltas should have started to prograde seawards. However, previous studies revealed that the progradation of modern deltas was initially very slow, and more importantly, sediment accumulation within central deltaic basins was exceptionally low between 7000 and 4000 cal. a BP. In order to investigate the main reasons for such slow progradation and low sedimentation during the middle Holocene, this study reconstructed the sedimentary history of the head area of the Pearl River delta. The results show marine transgression from 9500 to 7500 cal. a BP, followed by marine regression starting from 7500 to 4000 cal. a BP, in response to sea-level change. During the latter period, sedimentation was concentrated in the head area. The amount of sediment entering the central basin was significantly reduced. This limited amount of sediment was spread thinly across the wide deltaic basin. A portion of it could have been transported out into the South China Sea by the strong tidal currents, resulting in an exceptionally low sedimentation in the central basin. However, in locations adjacent to former/present islands, locally supplied sediment helped sedimentation to continue from 7500 to 4000 cal. a BP. By about 4000 cal. a BP, the deltaic shoreline advanced into the central basin. This period saw an increase of human activity that caused soil erosion and sediment supply, leading to a marked increase in sedimentation rate. Active land reclamations also helped the acceleration of shoreline advance. This sedimentary evolution model in the Pearl River delta mirrors those of other deltas in the monsoonal Asia. • New sedimentary core records were reported for the head area of the PRD. • A three-stage history of the landform evolution in the head area was reconstructed. • Holocene sediment accumulation models were identified for the head area, central wide deltaic basin and peri-island area. • Reasons for the mid-Holocene low sedimentation in the PRD were discussed along with other Asian deltas. [ABSTRACT FROM AUTHOR]

The persistence and prevalence of microplastics in the environment have raised concerns among scientists, the general public, and environmental regulatory agencies, and a large number of studies on microplastics in sediments have been published. We reviewed those studies and focused on understanding the spatial and temporal variations, biological effects, and analytic methods of microplastics in sediments. Microplastics are widely distributed in marine and freshwater sediments. The distribution of microplastics is mainly influenced by anthropogenic input and environmental processes that determine the transportation, transformation and accumulation. The appearance of microplastics in sedimentary records has been proposed as a stratigraphic marker for the onset of the Anthropocene Epoch. Our current understanding of biological effects of microplastics is based mainly on field research and laboratory-scale experiments using unrealistic concentration and limited forms of microplastics. Future studies should consider environmentally relevant concentration, the diverse composition and form of microplastics presenting in the natural environment. Density separation method for separation of microplastics in sediments is the most commonly used, and component identification by optical analysis (Fourier-transform infrared spectroscopy spectra, Raman spectra etc.) are important analytic methods. Yet the separation method remains to be standardized across laboratories. Other separation methods include electrostatics separation, organic solvent extraction and magnet separation. We recommend the combination of density separation, electrostatic separation and organic solvent separation to improve the separation efficiency of microplastics and to standardize the analytic process for sediment microplastics in future studies. [ABSTRACT FROM AUTHOR]

Over the past few decades, studies on the Indian Summer Monsoon (ISM) have been mainly based on paleo-marine records whilst the sparsity of land records limits our understanding of the ISM evolutionary process over continental landscapes. Here, we provide paleoclimate reconstructions based on n -alkanes and branched glycerol dialkyl glycerol tetraethers (brGDGTs) from a 50-ka lacustrine sediment core collected from Lake Tengchong Qinghai in southwestern subtropical China. Our results reveal that the botanical sources of sedimentary n -alkanes in this lake are mainly from aquatic macrophytes and terrestrial plants. The lake level evolution from the MIS 3 to the Holocene can be divided into four stages: high in the MIS 3, low in the LGM, high in last deglacial and low in mid and late Holocene. Our brGDGTs-based climate reconstructions indicate that the mean air temperature differences between the present-day and the LGM were up to about 3–4 °C. From MIS 3 to Holocene, there was a broadly and consistently synchronous trend between precipitation and air temperature in this ISM region. This is different from the asynchronous temperature and precipitation variations in the East Asian Summer Monsoon (EASM) regions in the period of last glacial termination. Our study shows that the climate in ISM regions was primarily driven by changes in June summer solar insolation at 30°N, and those glacial boundary conditions such as ice volume and sea surface temperature might also have affected the ISM. • Records of effective moisture, precipitation and temperature covering the last 50 ka. • The MAT difference between LGM and the present-day is about 3–4 °C. • Temperature and precipitation have changed broadly synchronously in this ISM dominating area. [ABSTRACT FROM AUTHOR]

The well-preserved Maoshan paddy fields (4700–4300 bp) were built on an intermediate landscape between the foothills and alluvial plain of the Lower Yangtze River. Despite several interdisciplinary research, there has been a lack of detailed environmental and ecological data to contextualise the reconstructed rice farming practices within a wider paleo-environmental background. Our research provides key information on the chronology, vegetation, and long-term hydrological fluctuations at and surrounding the paddy fields. Our 14C and OSL dates show that the initial occupation began at around 5740 ± 140 cal. bp, and the paddy fields were built at around 4675 ± 145 cal. bp and were in use continuously until around 4000 cal. bp. Our pollen, diatom and phytolith data shows that whilst the vegetation in the field was sensitive to changes caused by water management and rice farming, the ecological system surrounding the fields was relatively stable. We suggest that this high frequency of in-field vegetation changes was closely related to intensifying water management for rice farming. This thesis is supported by our geophysical and geochemical analyses of bulk sediments, which shows that the steady build-up of the alluvial sequence was punctuated by several short-term episodes of high-energy surface runoff, including strong flushing in of sandy sediments into the fields perhaps through irrigation activities. Our paleo-ecological and geoarchaeological investigation at Maoshan permits an overview of the development of rice farming and intensifying water management practices in a wider environmental context and offers significant insights to the ongoing debate on the wet-dry dichotomy of early rice farming. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS), situated to the north of the Indo-Pacific Warm Pool (IPWP), is under the strong influence of the Asian monsoon system. However, coastal sea surface temperature (SST) records from the SCS, which are of vital importance to exploring ocean-atmosphere-land interactions behind the Asian monsoon system, remain scarce. Here, we use a sediment core collected at the coast of northern SCS to investigate alkenone-SST variations over the past two millennia. On multi-centennial timescale, SST changes in our record exhibit an opposite pattern to that of Northern Hemisphere temperature and solar irradiance, for example, relatively cool SST during the Medieval Warm Period (MWP) and warm conditions during the Little Ice Age (LIA). Together with alkenone content and existing records, we suggest that the regional SST changes result from a strengthening (weakening) of wind-driven coastal upwelling, associated with variability of the Asian summer monsoon intensity during the MWP (LIA). [ABSTRACT FROM AUTHOR]

In order to reconstruct the environmental conditions of marine isotope stage (MIS) 5 in the coastal area of northern South China Sea, a sediment core was collected from the south coast of Hainan Island (18°16′57″N, 109°42′38″E), from which a thick marine mud unit (39 m) is found to be the deposit of MIS 5. According to the high abundance of alkenones, the thick mud sequence was deposited under marine conditions. The high TOC and n -alkanes concentrations (as normalized to TOC) suggest this was a period of high organic matter (OM) production, and the majority of OM came from terrestrial vascular plant sources. Comparatively, short chain n -alkanes (C 18-22 ) and proportion of aquatic plant index ( P aq) in the lower sub-unit appear higher than those in the middle and upper sub-units, suggesting a gradual increase in terrestrial OM supply throughout MIS 5e. The carbon preference index in long-chain n -alkanes (CPI 25-33 ) implies high precipitation and/or temperature in this interval, whilst the average carbon length index in long-chain n -alkanes (ACL 25-33 ) indicates a warm climate during MIS 5e. [ABSTRACT FROM AUTHOR]

Quantitative proxy-based and high-resolution palaeoclimatic datasets are scarce for the lower reaches of the Yangtze River (LYR) basin. This region is in a transitional vegetation zone which is climatologically sensitive; and as a birthplace for prehistorical civilization in China, it is important to understand how palaeoclimatic dynamics played a role in affecting cultural development in the region. We present a pollen-based and regionally-averaged Holocene climatic twin-dataset for mean total annual precipitation (PANN) and mean annual temperature (TANN) covering the last 10,000 years for the LYR region. This is based on the technique of weighted averaging-partial least squares regression to establish robust calibration models for obtaining reliable climatic inferences. The pollen-based reconstructions generally show an early Holocene climatic optimum with both abundant monsoonal rainfall and warm thermal conditions, and a declining pattern of both PANN and TANN values in the middle to late Holocene. The main driving forces behind the Holocene climatic changes in the LYR area are likely summer solar insolation associated with tropical or subtropical macro-scale climatic circulations such as the Intertropical Convergence Zone (ITCZ), Western Pacific Subtropical High (WPSH), and El Niño/Southern Oscillation (ENSO). Regional multi-proxy comparisons indicate that the Holocene variations in precipitation and temperature for the LYR region display an in-phase relationship with other related proxy records from southern monsoonal China and the Indian monsoon-influenced regions, but are inconsistent with the Holocene moisture or temperature records from northern monsoonal China and the westerly-dominated region in northwestern China. Overall, our comprehensive palaeoclimatic dataset and models may be significant tools for understanding the Holocene Asian monsoonal evolution and for anticipating its future dynamics in eastern Asia. [ABSTRACT FROM AUTHOR]

How tropical hydroclimate and ecosystems in Asia have varied on orbital timescales has been an important topic for decades. The northern boundary of tropical Asia under strong influence of monsoon system has been highly sensitive to global climate changes on orbital timescales. Among the available proxy data, limited terrestrial evidence of glacial-interglacial variation of vegetation impedes the understanding of tropical climate dynamics. Here, we report a lacustrine record covering the last 150 kyrs from a tropical maar paleolake located between the Asian landmass and the South China Sea. Our pollen and δ13C results consistently show strong glacial-interglacial variability of vegetation changes between savanna dominated by C 4 herbs and rainforest characterized by C 3 trees over the past 150 kyrs. The glacial/stadials with C 4 herb dominance during MIS6, 4 and 2 corresponded to drier conditions with rainfall amounts <650 mm/yr, which has been considered as the climatic threshold for the growth of savanna biome. The vegetation variations in relation to large-amplitude variations of regional hydroclimate were tightly coupled with the internal glacial forcings (e.g., global ice volume) in addition to external insolation, and coincided with changes in sea level/continental shelf exposure and sea surface temperature in the northern South China Sea. These significant correlations suggest a more important role of glacial forcings than insolation in controlling tropical hydroclimate and vegetation changes, which is transmitted and amplified by tropical warm pool environments (i.e., spatial extent of shelf exposure and water temperature). • A high-resolution pollen and δ13C record covering the past 150 kyrs in tropical Asia. • Consistent evidence of savanna/rainforest alternations during last glacial cycles. • Climate reconstruction showed significant drops in rainfall during the glacials. • Ice-forcing environmental changes were crucial for climate dynamic in tropical Asia. [ABSTRACT FROM AUTHOR]

Our understanding on the spatial-temporal patterns of climatic variability over the last few millennia in the East Asian monsoon-dominated northern China (NC), and its role at a macro-scale in affecting the prosperity and depression of Chinese dynasties is limited. Quantitative high-resolution, regionally-synthesized palaeoclimatic reconstructions as well as simulations, and numerical analyses of their relationships with various fine-scale, numerical agro-ecological, social-economic, and geo-political historical records during the period of China's history, are presented here for NC. We utilize pollen data together with climate modeling to reconstruct and simulate decadal- to centennial-scale variations in precipitation or temperature for NC during the last 2200 years (-200–2000 AD). We find an overall cyclic-pattern (wet/warm or dry/cold) in the precipitation and temperature anomalies on centennial- to millennial-scale that can be likely considered as a representative for the entire NC by comparison with other related climatic records. We suggest that solar activity may play a key role in driving the climatic fluctuations in NC during the last 22 centuries, with its quasi ∼100, 50, 23, or 22-year periodicity clearly identified in our climatic reconstructions. We employ variation partitioning and redundancy analysis to quantify the independent effects of climatic factors on accounting for the total variation of 17 fine-grained numerical Chinese historical records. We quantitatively illustrate that precipitation (67.4%) may have been more important than temperature (32.5%) in causing the overall agro-ecological and macro-geopolitical shifts in imperial China with NC as the central ruling region and an agricultural heartland over the last 2200 years. [ABSTRACT FROM AUTHOR]

The early Holocene environmental amelioration stimulated the trajectory of Neolithic farming cultures and specific geographic settings played a role in determining the nature of these cultures. Using microfossil evidence, the present study reveals that the fluctuations of the groundwater table substantially influenced rice domestication in the Dongting Lake area of the middle Yangtze River basin in the early Holocene. Our 14 C-dated sediment core taken from the Bashidang (BSD) Neolithic site contains evidence that the site was a floodplain prior to human occupation ca . 8600 years ago. Poaceae, which contained wild rice ( Oryza sp.) as indicated by combined pollen and phytolith evidence, and low counts of freshwater algae indicated a moist site condition. The area then gradually evolved into wetlands as the water table rose, in response to the increasing monsoon precipitation during the early Holocene. This favored rice domestication, assisted by firing and clearing, that continued to flourish for several hundred years. Finally, rice domestication declined during the late stage of the Pengtoushan culture, accompanied by evidence of the expansion of wetlands reflecting the effects of a rising groundwater table that had caused the cessation of rice farming at the Bashidang site after ca. 8000-7900 cal yr BP. This study shows that there are local effects at particular sites that may differ from the trend at the regional scale, necessitating a careful interpretation of the available evidence. [ABSTRACT FROM AUTHOR]

As one of the most densely populated areas in the world, the Pearl River delta has been well studied in its postglacial sedimentary stratigraphy and the effects of Holocene sea-level rise. However, the effects of fluvial force on its geomorphological evolution are much less understood. This paper analyzed the Holocene sedimentary archives and reconstructed the geomorphologic history of an area where the West and North Rivers join and enter the deltaic basin. The reconstruction is based on the analyses of particle size, total organic carbon, organic carbon isotope ratios and microfossil diatoms of five radiocarbon-dated core sediments. The results show rapid paleo-incised valley infilling since c. 9500 cal. a BP, in response to sea-level rise. During marine regression starting from c. 8000 cal. a BP, a bifurcation occurred, and a mouth bar was developed. While the mouth bar emerged to mean tide level around c. 5500 cal. a BP, the surrounding estuarine subtidal flats were gradually transformed into tidal wetlands by c. 3000 cal. a BP. The immediate adjacent waters to the mouth bar were gradually infilled from c. 3000 cal. a BP onwards which narrowed the distributary channels. This landform evolution in the head area of the Pearl River delta resulted in the gradually strengthening fluvial force and weakening tidal force since the relative sea level approached its stabilization. During the past 3000 years, the continuous strengthening of fluvial force supported the accretion of deltaic floodplains. The discovery of mouth bar formation, channel narrowing and deltaic floodplain accretion in this location brings a new perspective of scientific investigation to river delta geomorphologic evolution in response to natural and anthropogenic factors. • The first mouth bar and bifurcation of the Pearl River delta are identified. • Geomorphologic evolution of the mouth bar and delta plains are reconstructed. • Strengthening fluvial force played a key role in the development of the delta plain. [ABSTRACT FROM AUTHOR]

This study concerns high-resolution sea surface temperature (SST) changes for the Eemian interglacial period reconstructed from the southern coast of Hainan Island, China. The lower marine unit in the sediment core is composed of monotonous mud (31 m thick), dated to be from the Eemian interglacial period or lower part of marine isotope stage 5 (MIS 5), determined by optically stimulated luminescence (OSL). The high sedimentation rate and the richness of organic matter and marine fossils provide good opportunity for the study of palaeo-environments in the northern margin of the South China Sea (SCS). Sediment grain-size, foraminifer, sediment color index and long-chain alkenone were used to reveal the near-shore sedimentary environments and temperature at millennial-scale. Specifically, a high-resolution U K′ 37 -SST record was reconstructed for the Eemian interglacial period. The new evidence in northwestern margin of SCS shows that the maximum value of SST during the Eemian interglacial is approximately 29 °C and the lowest is 26.5 °C. The trend of decreasing SST from 29 °C throughout the marine sequence is consistent with the variations in sediment grain size, reflecting the cooling trend of SST and sea-level lowering tendency during the last interglacial period. This new Eemian SST result agrees with other records in the region of SCS, showing a coherent descending trend, but spatial heterogeneity exists in timing and amplitude. The insolation changes might be the main force for initiating the SST evolution during the penultimate interglacial period. [ABSTRACT FROM AUTHOR]

This study presents a new model of Holocene ice-volume equivalent sea level (ESL), extending a previously published global ice sheet model (Bassett et al., 2005), which was unconstrained from 10 kyr BP to present. This new model was developed by comparing relative sea level (RSL) predictions from a glacial isostatic adjustment (GIA) model to a suite of Holocene sea level index points from China and Malay-Thailand. Three consistent data-model misfits were found using the Bassett et al. (2005) model: an over-prediction in the height of maximum sea level, the timing of this maximum, and the temporal variation of sea level from the time of the highstand to present. The data-model misfits were examined for a large suite of ESL scenarios and a range of earth model parameters to determine an optimum model of Holocene ESL. This model is characterised by a slowdown in melting at ∼7 kyr BP, associated with the final deglaciation of the Laurentide Ice Sheet, followed by a continued rise in ESL until ∼1 kyr BP of ∼5.8 m associated with melting from the Antarctic Ice Sheet. It was not possible to identify an earth viscosity model that provided good fits for both regions; with the China data preferring viscosity values in the upper mantle of less than 1.5 × 10 20 Pa s and the Malay-Thailand data preferring greater values. We suggest that this inference of a very weak upper mantle for the China data originates from the nearby subduction zone and Hainan Plume. The low viscosity values may also account for the lack of a well-defined highstand at the China sites. [ABSTRACT FROM AUTHOR]

The climate history over the past few centuries is important to be used to assess how regional climate responds to global forcing. Here we report three high-resolution alkenone-based sea surface temperature (SST) records over the past 4 centuries from three sediment cores collected in the Mirs Bay, northeastern Hong Kong. All three SST records consistently show a general cooling trend toward the present, with most of cooling occurring over the last century. Alkenone-derived SST values stayed around 26.5–27 °C at the three sites prior to 1900s and decreased into the range of 25–26 °C. The magnitude of cooling approximately from the Little Ice Age (LIA) to present tends to be dampened from ∼2 °C nearshore to ∼1 °C offshore. The cooling trend, as identified in all three SST records, is thus opposite to the global temperature rise over the last century. Assisted with modern observations, we interpret that the alkenone-derived SST reflects increasing upwelling in the Mirs Bay, which likely results from the strengthened East Asian summer monsoon, in the context of global warming over the last century. [ABSTRACT FROM AUTHOR]

Pollen from a series of surface soil samples collected along a transect spanning southeast China was investigated to better understand palynological signals of ancient agriculture and other human activity. The transect surface samples consist of pairs taken inside and outside rice paddy fields. Pollen assemblages from these samples are valuable as modern analogs of human-altered environments and rice agriculture. Our measurements of Poaceae pollen grains from inside the modern rice fields discovered that 34–40 µm is the statistically significant size range for identifying domesticated rice in fossil pollen samples. This conclusion is also based on a size comparison of raw and chemically treated modern pollen grains from the plants. Pollen measurements for local wild grasses show that most native weeds have pollen grains less than 30 µm in size. The modern analogs and our study of the influence of chemical treatment on pollen grain size made it possible to examine a sediment core from the Pearl River delta for evidence of anthropogenic influence, including rice farming. Pollen assemblages from around 2200 cal. yr BP are highly similar to those of our modern analogs representing disturbed landscapes outside modern rice fields. The pollen spectra reveal abrupt increases in Poaceae, Dicranopteris, Artemisia and Pinus indicative of rice farming and forest clearance, at around 2200 cal. yr BP. Major factors associated with this abrupt transition were the rapid formation of the deltaic flood plain and massive increases in the Pearl River delta area population during the Qin Dynasty. [ABSTRACT FROM AUTHOR]

Abstract: The East Asian marginal seas are important sinks of terrigenous materials transported by large rivers. In this study two cores from the Changjiang (Yangtze River) and Zhujiang (Pearl River) estuaries and one core from the inner shelf off of Hong Kong were investigated to examine the burial of organic matter during the postglacial period and its possible links with paleoenvironmental changes. Based on a simple two end-member mixing model, the terrestrial organic matter supplied primarily from the Zhujiang and Changjiang dominates the estuarine areas while marine organic matter contributes more to the inner-mid shelf. The competing contributions of terrestrial and marine organic matter are responsible for the downcore variations of organic elemental compositions. The overall decreasing shifts of total organic carbon concentrations and total organic carbon to total nitrogen ratios in the Zhujiang estuarine sediments since 6.5kaBP seems to support the notion that depth profiles of organic matter compositions deposited in the Zhujiang Estuary can aid in the reconstruction of monsoon history in the Holocene. Nevertheless, organic matter compositions in the Changjiang Estuary and inner shelf off of southeastern Hong Kong respond in a different and more complex way to freshwater discharges or precipitation changes (monsoon variability) in the catchments, owing to complex controls of deposition and preservation of organic matter in these estuarine and shelf environments. Caution is therefore needed in using organic elemental and isotopic compositions to decipher paleoenvironmental changes in East Asian continental shelves where intense river–sea interactions occur and sedimentary environments change drastically. [Copyright &y& Elsevier]