Ice rafting history and paleoceanographic reconstructions of Core 08P23 from southern Chukchi Plateau, western Arctic Ocean since Marine Isotope Stage 3

Multiproxy investigations have been performed on Core 08P23 collected from the Chukchi Plateau, the western Arctic Ocean, during the Third Chinese National Arctic Expedition. The core was dated back to Ma-rine Isotope Stage （MIS） 3 by a combination of Accelerator Mass Spectrometric （AMS） carbon-14 dating and regional core correlation. A total of five prominent ice-rafted detritus （IRD） events were recognized in MIS 2 and MIS 3. The IRD sources in MIS 3 are originated from vast carbonate rock outcrops of the Canadian Arctic Archipelago and clastic quartz in MIS 2 may have a Eurasian origin. Mostδ18O andδ13C values of Neogloboquadrina pachyderma （sinistral） （Nps） in Core 08P23 are lighter than the average values of surface sediments. The lighterδ18O andδ13C values of Nps in the two brown layers in MIS 1 and MIS 3 were resulted from meltwater events; and those in the gray layers in MIS 3 were caused by the enhanced sea ice formation. Theδ18O values varied inversely withδ13C in MIS 2 indicate that the study area was covered by thick sea ice or ice sheet with low temperature and little meltwater, which prevented the biological productivity and sea-atmosphere exchange, as well as water mass ventilation. The covaried light values ofδ18O andδ13C in MIS 1 and MIS 3 were resulted from meltwater and/or brine injection.

Paleo-Fluvial Systems during Marine Isotope Stages 6, 4 and 2 in the North Yellow Sea

Objective During the sea-level lowstands of the Late Quatemary, paleo-channels resulting from large-scale glacial regressions were extensively developed on continental shelves worldwide. Great attention has been paid to the mechanisms and ages of these successions of fluvial incisions, which provide insight into the sedimentary evolution and processes of shelves.

A warmer but drier Marine Isotope Stage 11 during the past 650 ka as revealed by the thickest loess on the western Chinese Loess Plateau

Marine Isotope Stage 11（MIS 11; ca. 423-362 ka） is generally considered to be the best analogue for the present interglacial（Holocene）, and investigation of it will improve our understanding of current climate variability and assist in predictions of future climate change. However, many recent studies primarily focus on the structure and duration of MIS 11. Little research has focused on climate warmth and stability recorded in the Chinese loess-paleosol sequences（LPS） during the S4 paleosol formation（equivalent to MIS 11）. On the basis of previous work, this study presents a high-resolution record（ca. 75 a/cm） that spans from MIS 1 to MIS 15, as preserved in the thickest known Jingyuan loess section on the western Chinese Loess Plateau（CLP）. This LPS is almost 165 m thick and was sampled from the upper part of L6 to the modern soil at 2-cm depth intervals. Measurements of magnetic susceptibility, mean grain size and ＆gt;63 μm particle content, carbonate content, total organic carbon, and soil color of samples were made to reconstruct the paleoclimate variation, and a grain-size age model was used to constrain the chronological framework. The primary results show that a generally warm-humid climate dominated the S4 paleosol development, but the climate condition was extremely unstable during the whole of MIS 11. Two obviously different climate regimes controlled the MIS 11 climate variation： the early part of MIS 11 was extremely warm and stable, but the latter part was relatively cool（non-glacial） and unstable. This climate pattern was consistent with records on the central CLP and wavelet analysis suggested that it was forced by the 65°N insolation variability modulated by a quasi-100-ka cycle. In addition, a multi-proxy comparative study on the climate conditions during S0 to S5 paleosol development indicates that the period of S4 development might be the warmest interglacial of the past 650 ka. However, the climate condition during S4 development was not the most humid episode as recorded in Xifeng and Luochuan loess sections on the central CLP. On the contrary, it was drier than both the MIS 15 and the present interglacial on the western CLP, which is somewhat similar to the present climate pattern on the central CLP.

Centennial-scale monsoon collapses during Marine Isotope Stage(MIS)7e detected in a northern Chinese stalagmite record

Occurrence or absence of centennial-scale climatic variability during Marine Isotope Stage(MIS)7e,the first peak interval of the Penultimate Interglacial,remains ambiguous due to the limited available high-resolved records.Here,we present a decadal-resolved stalagmiteδ^(18)O record from northern China spanning from 242.3 to 236.8 ka BP,covering MIS7e.The composite KLSδ^(18)O record,integrating this study with the previous record in the same cave,shows a descending trend from TerminationⅢto MIS7e,which follows the increasing Northern Hemisphere summer insolation(NHSI).This observation further emphasizes the important influence of NHSI on the glacial/interglacial transition.There are more large-amplitude,millennial-to centennial-scale variability occurring during TerminationⅢcompared with MIS7e,implying that ice-sheet decay potentially plays an important role in climatic excursions.Four centennial-scale summer monsoon collapses,peaking at~242.1,~240.8,~239.3 and~238.2 ka BP,are detected in our new record,indicating the pervasiveness of the intra-interglacial climatic instability.Given the lack of solar activity and freshwater outbursts data during MIS7e,it is not possible to conclude about the drivers of the identified abrupt climatic anomalous.Following the dynamic mechanisms of sub-millennial climatic anomalous during early Holocene,we tentatively propose that slowdown of the meridional overturning circulation caused by freshwater fluxes into North Atlantic and/or attenuated solar irradiance is the potential forcing for the abrupt climate events within MIS7e.Additionally,attenuated solar irradiance could also result in climatic anomalies through low-latitude processes.

Late Quaternary fluvial terrace formation in the Luan River drainage basin,north China and its possible linkages with climate change and tectonic activation

The Luan River is the most important water system in north-eastern Hebei Province,China and is located in the transitional zone of the Eastern Yan Mountains,North China Plain and Songliao Plain.The well-developed river terraces of its tributary,the Yixun River,provide excellent information for studying neotectonics and climate change.There are seven terraces in the lower reaches of the Yixun River,numbered T7-T1.The optically stimulated luminescence dating results of 23 samples show that terraces T7-T2 formed at 111.36±5.83 ka,78.20±4.45 ka,65.29±4.15 ka,56.44±3.07 ka,40.08±2.66 ka,and 13.14±0.76 ka,respectively.A comparison with the oxygen isotope curves of deep-sea sediments reveals that the sediment formation of each terrace corresponded to cold periods of marine isotope stages MIS 4 and MIS 2 and the relatively cold periods of MIS 5e,MIS 3,and MIS 1.Since the Late Pleistocene,the incision rate of the Yixun River has ranged from 0.371-1.740 mm/a.During the formation of T7-T6,T5-T4,T4-T3,and T3-T2,the incision rate was low.However,in the two stages during which T6-T5 and T2-T1 formed(13.14±0.76 ka to 0.58±0.08 ka and 10.79±0.64 ka to 0.16±0.01 ka),these rates reached 1.554 mm/a and 1.592-1.740 mm/a,respectively.At approximately 30 ka,the activity of the Langying Fault increased,leading to footwall uplift.The river gathered in the north of Langying to form the ancient Erdaowan Lake,which resulted in the drying of the river in the lower reaches of the Yixun River during the last glacial maximum without forming river deposits.In the Early Holocene,headward erosion in the lower reaches of the Yixun River was enhanced,which resulted in the disappearance of the lake,and incised meandering formed due to increased neotectonism.Based on the analyses of river incision and the formation of ancient lakes and incised meandering,it was inferred that there have been three periods of strong tectonism in the river basin since the Late Pleistocene.

Soil Properties in Two Soil Profiles from Terraces of the Nam Co Lake in Tibet,China

This article investigates the soil properties in two soil profiles from the terraces of the Nam Co Lake in Tibet,China. Profile 1,with a slope aspect to east,is 37 m,and profile 2,to southwest,is 32 m above the lake level. Twelve and nine layers were identified in profile 1 and profile 2,respectively,based on the color,texture,structure,moisture content,presence of carbonate,and root density. Grain sizes and measurements of water content,total organic carbon,total inorganic carbon,total carbon,pH value and electrical conductivity were all analyzed for each sample. The results show that soil is poorly developed because of sparse vegetation coverage and weak chemical weathering in the cold and arid area. The results also indicate that the soil properties are different between the two profiles and suggest that soil is better developed in profile 1 than in profile 2. These differences are ascribed to the dissimilarity of landform,vegetation and timing. Profile 1 faces to east as compared with profile 2 facing to southwest and gets less insolation and therefore less evaporation. Thus,vegetation grows better in profile 1 than in profile 2. Radiocarbon dating and OSL dating show that profile 1 underwent a longer soil forming process than profile 2,which is helpful for the soil development in profile 1.

Grain-size Characteristics and Climate Variability in TMS5e Sequence of Tumen Section in Southern Tengger Desert,Northwestern China

The TMS5e sequence from the Tumen section, at the southern edge of Tengger Desert in the northwestern China, is synchronous with Marine Isotope Stage 5e （MIS5e）. It consists of 16 layers of aeolian dune sands, 11 layers of lacustrine loess-like facies, and 5 layers of lacustrine facies. The results of grain-size analysis shows that the pa- laeo-mobile dune sands, palaeo-fixed to semi-fixed dune sands and loess-like sandy loams are mainly composed of sands, ranging from 70% to 96%; their silt contents ranged from 4% to 20%, and their clay contents ranged from 1% to 5%; the climate under which the aeolian dune sands were deposited is similar to that under which modern mobile dune sands form, which is caused by the dominance of the cold, dry East Asian winter monsoon. In contrast, the lacustrine loess-like facies and lacustrine facies had a lower sand contents than those of the three aeolian dune sands, but have higher silt and clay contents, most of their sand content ranged from 30% to 60%, their silt contents ranged from 35% to 55%, and their clay contents ranged from 6% to 20%. The lacustrine loess-like facies and lacustrine facies formed under the influence of the warm, humid East Asian summer monsoon based on their similarity with modern sediments. The grain-size indicator Mz （mean grain diameter） and the SC/D value in the TMS5e sequence indicate climatic insta- bility at the southern edge of the Tengger Desert during MIS5e, with at least 14 fluctuations between a warm, humid climate and a cold, dry climate, divided into five stages： TMS5e5 （139 kyr to 129.3 kyr B.P.）, TMS5e4 （129.3 kyr to 124 kyr B.P.）, TMS5e3 （124 kyr to 119.5 kyr B.P.）, TMS5e2 （119.5 kyr to 116.5 kyr B.P.）, and TMS5el （116.5 kyr to 113.7 kyr B.P.）. These correspond roughly to MIS5e5, MIS5e4, MIS5e3, MIS5e2, and MIS5el, respectively, in the GRIP ice core data.

Evolution of sedimentary environments of the middle Jiangsu coast, South Yellow Sea since late MIS 3

An evolutionary model of sedimentary environments since late Marine Isotope Stage 3 （late MIS 3, i.e., ca. 39 cal ka BP） along the middle Jiangsu coast is presented based upon a reinterpretation of core 07SR01, new correlations between adjacent published cores, and shallow seismic profiles recovered in the Xiyang tidal channel and adjacent northern sea areas. Geomorphology, sedimentology, radiocarbon dating and seismic and sequence stratigraphy are combined to confirm that environmental changes since late MIS 3 in the study area were controlled primarily by sea-level fluctuations, sediment discharge of paleo-rivers into the South Yellow Sea （SYS）, and minor tectonic subsidence, all of which impacted the progression of regional geomorphic and sedimentary environments （Le., coastal barrier island freshwater lacustrine swamp, river floodplain, coastal marsh, tidal sand ridge, and tidal channel）. This resulted in the formation of a fifth-order sequence stratigraphy, comprised of the parasequence of the late stage of the last interstadial （Para-Sq2）, including the highstand and forced regressive wedge system tracts （HST and FRWST）, and the parasequence of the postglacial period （Para-Sql）, including the transgressive and highstand system tracts （TST and HST）. The tidal sand ridges likely began to develop during the postglacial transgression as sea-level rise covered the middle Jiangsu coast at ca. 9.0 cal ka BP. These initially submerged tidal sand ridges were constantly migrating until the southward migration of the Yellow River mouth to the northern Jiangsu coast during AD 1128 to 1855. The paleo-Xiyang tidal channel that was determined by the paleo-tidal current field and significantly different from the modern one, was in existence during the Holocene transgressive maxima and lasted until AD 1128. Following the capture of the Huaihe River in AD 1128 by the Yellow River, the paleo-Xiyang tidal channel was infilled with a large amount of river-derived sediments from AD 1128 to 1855, causing the emergence of some of the previously submerged tidal sand ridges. From AD 1855 to the present, the infilled paleo-Xiyang tidal channel has undergone scouring, resulting in its modern form. The modern Xiyang tidal channel continues to widen and deepen, due both to strong tidal current scouring and anthropogenic activities.