The baroclinic circulation structure of Yellow Sea Cold Water Mass

The Yellow Sea is a semi-enclosed shallow sea with a deep trough of about 80 m. On the hy-drographic condition in the Yellow Sea, Lie[1] pointed out that it is strongly associated with winter cooling and summer heating, fresh input from rivers into the co…     

A quantitative reconstruction of the paleoenviornmental variations of the South Yellow Sea inner shelf based on benthic foraminiferal transfer functions

Transfer functions between the benthic foraminiferal fauna of seventy-one sediment surface-samples retrieved from the South Yellow Sea inner shelf and the environmental factors, including the summer bottom-water salinity(Ss), the summer bottom-water temperature(Ts) and the winter bottom-water temperature(Tw) have been developed utilizing weighted averaging partial least square regression(WA-PLS). Subsequently, the transfer functions have been applied to a late Holocene piston core SY01 from the South Yellow Sea inner shelf, established the variation curves of the Ss, Ts, and Tw during the last 3.9 cal. ka. The Ss and Ts showed a nearly synchronous trend to the published stalagmite δ18O curve from the Jiuxian Cave, meaning they could be used as reliable indicators for the summer monsoon. Similarly, the Tw could be used as an indicator for the winter monsoon for its synchronous change to the insensitive grain size variation of the core ZY-2 retrieved from the Central Yellow Sea mud area. These results suggest that transfer functions based on benthic foraminiferal fauna can be a potentially useful tool in palaeoceanographic and palaeoenvironmental research along the Chinese seaboard.     

Evolution of the East China Sea sedimentary environment in the past 14 kyr: Insights from tetraethers-based proxies

We reconstruct the environmental evolution of the East China Sea in the past 14 kyr based on glycerol dialkyl glycerol tetraethers(GDGTs) in a sediment core from the subaqueous Yangtze River Delta. Two primary phases are recognized. Phase I(13.8–8 cal kyr BP) reflects a predominantly continental influence, showing distinctly higher concentrations of branched GDGTs(averaged 143 ng/g dry sediment weight, dsw) than isoprenoid GDGTs(averaged 36 ng/g dsw), high BIT index(branched vs. isoprenoid tetraethers) values(0.78) and a fluctuating GDGT-0/crenarchaeol ratio(R_(0/5), varied from 0.52 to 3.81). Within this interval, temporal increases of terrestrial and marine influence are attributed to Younger Dryas(YD)(ca. 12.9–12.2 cal kyr BP) cold event and melt-water pulse(MWP)-1B(11.5–11.1 cal kyr BP), respectively. The prominent transition from 8 to 7.9 cal kyr BP shows a sharp decrease in BIT index value(0.4) and increase in crenarchaeol, which marks the beginning of phase II. Afterwards, the proxies remain relatively constant, which indicates that phase II(7.9 cal kyr BP-present) is a shelf sedimentary environment with high stand of sea level. Overall, the BIT index in our record serves as a good marker for terrestrial influence at the site, and likely reflects the flooding history of the region. The TEX_(86)(Tetra Ether Index of tetraethers consisting of 86 carbons) proxy is not applicable in phase I because of an excess terrestrial influence; but it seems to be valid for revealing the annual SST in phase II(21.6±0.9°C, n=49). In contrast, the MBT'/CBT(Methylation of Branched Tetraethers and Cyclization of Branched Tetraethers) proxy appears to faithfully record the annual mean air temperature(MAT)(14.3±0.63°C, n=68) and presents an integrated signal over the middle and lower Yangtze River drainage basin.     

High precision glacial–interglacial benthic foraminiferal Sr/Ca records from the eastern equatorial Atlantic Ocean and Caribbean Sea

Glacial–interglacial variation in the marine Sr/Ca ratio has important implications for coral Sr thermometry [J.W. Beck et al., Science 257 (1992) 644–647]. A possible variation of 1–3% was proposed based on ocean models [H.M. Stoll and D.P. Schrag, Geochim. Cosmochim. Acta 62 (1998) 1107–1118]. Subsequently, studies have used fossil foraminifera to test this prediction [P.A. Martin et al., Geochem. Geophys. Geosyst. 1 (1999); H.M. Stoll et al., Geochim. Cosmochim. Acta 63 (1999) 3535–3547; H. Elderfield et al., Geochem. Geophys. Geosyst. 1 (2000)]. But whether some component of foraminiferal Sr/Ca variation can be uniquely ascribed to seawater Sr variation is still not clear. To address this question, we developed cleaning and analysis techniques and measured Sr/Ca ratios on individual shells of the modern benthic foraminifer Cibicidoides wuellerstorfi. We showed that different size shells have different Sr/Ca ratios; however, samples with shell sizes of 355–500 μm appear to have normally distributed Sr/Ca ratios (1σ=1.8%). For multi-shell measurements (with estimated errors of 0.12–0.39%), the ratio varied by as much as 7.2±0.5% during the last glaciation for two Caribbean records at the same site and by 3.7±0.5% over the past 40,000 yr for one record from the Sierra Leone Rise in the eastern equatorial Atlantic. The two Caribbean records are very similar indicating that the behavior of shell Sr uptake was identical locally and that the shell Sr/Ca ratio faithfully reflects the local environment. The Atlantic record differs from the Caribbean records by as much as several percent. Thus, the foraminiferal Sr/Ca changes cannot be solely due to changes in seawater Sr/Ca unless the glacial deep ocean had spatial variation in Sr/Ca well in excess of the modern ocean. Certain similarities between the three records do exist. Notably, the rate of change of Sr/Ca is similar between 9 and 0 ka (−0.25%/kyr) and between 25 and 16 ka (+0.16%/kyr). This suggests that during these intervals, benthic foraminiferal Sr/Ca was affected by similar large-scale variables. One of these variables may be the average marine Sr/Ca ratio; however, comparison with model predictions [H.M. Stoll and D.P. Schrag, Geochim. Cosmochim. Acta 62 (1998) 1107–1118] suggests other factors must also be considered. The discrepancies between the two sites may be related to the different water mass histories for the Caribbean and eastern Atlantic. Our results suggest that variation of the seawater Sr budget only partially contributed to C. wuellerstorfi Sr/Ca records, while other significant factors still need to be quantified. At present we cannot confidently determine past seawater Sr/Ca variation from our foraminiferal records.     

Changes in the mode of Southern Ocean circulation over the last glacial cycle revealed by foraminiferal stable isotopic variability

Benthic foraminiferal oxygen and carbon isotopic records from Southern Ocean sediment cores show that during the last glacial period, the South Atlantic sector of the deep Southern Ocean filled to roughly 2500 m with water uniformly low in δ¹³C, resulting in the appearance of a strong mid-depth nutricline similar to those observed in glacial northern oceans. Concomitantly, deep water isotopic gradients developed between the Pacific and Atlantic sectors of the Southern Ocean; the δ¹³C of benthic foraminifera in Pacific sediments remained significantly higher than those in the Atlantic during the glacial episode. These two observations help to define the extent of what has become known as the ‘Southern Ocean low δ¹³C problem’. One explanation for this glacial distribution of δ¹³C calls upon surface productivity overprints or changes in the microhabitat of benthic foraminifera to lower glacial age δ¹³C values. We show here, however, that glacial-interglacial δ¹³C shifts are similarly large everywhere in the deep South Atlantic, regardless of productivity regime or sedimentary environment. Furthermore, the degree of isotopic decoupling between the Atlantic and Pacific basins is proportional to the magnitude of δ¹³C change in the Atlantic on all time scales. Thus, we conclude that the profoundly altered distribution of δ¹³C in the glacial Southern Ocean is most likely the result of deep ocean circulation changes. While the characteristics of the Southern Ocean δ¹³C records clearly point to reduced North Atlantic Deep Water input during glacial periods, the basinal differences suggest that the mode of Southern Ocean deep water formation must have been altered as well.     

Evolution of permafrost in China during the last 20 ka

The formation and evolution of permafrost in China during the last 20 ka were reconstructed on the basis of large amount of paleo-permafrost remains and paleo-periglacial evidence, as well as paleo-glacial landforms, paleo-flora and paleofauna records. The results indicate that, during the local Last Glacial Maximum(LLGM) or local Last Permafrost Maximum(LLPMax), the extent of permafrost of China reached 5.3×106-5.4×106 km2, or thrice that of today, but permafrost shrank to only0.80×106-0.85×106 km2, or 50% that of present, during the local Holocene Megathermal Period(LHMP), or the local Last Permafrost Minimum(LLPMin). On the basis of the dating of periglacial remains and their distributive features, the extent of permafrost in China was delineated for the two periods of LLGM(LLPMax) and LHMP(LLPMin), and the evolution of permafrost in China was divided into seven periods as follows:(1) LLGM in Late Pleistocene(ca. 20000 to 13000-10800 a BP)with extensive evidence for the presence of intensive ice-wedge expansion for outlining its LLPMax extent;(2) A period of dramatically changing climate during the early Holocene(10800 to 8500-7000 a BP) when permafrost remained relatively stable but with a general trend of shrinking areal extent;(3) The LHMP in the Mid-Holocene(8500-7000 to 4000-3000 a BP)when permafrost degraded intensively and extensively, and shrank to the LLPMin;(4) Neoglaciation during the late Holocene(4000-3000 to 1000 a BP, when permafrost again expanded;(5) Medieval Warming Period(MWP) in the late Holocene(1000-500 a BP) when permafrost was in a relative decline;(6) Little Ice Age(LIA) in the late Holocene(500-100 a BP), when permafrost relatively expanded, and;(7) Recent warming(during the 20 th century), when permafrost continuously degraded and still is degrading. The paleo-climate, geography and paleopermafrost extents and other features were reconstructed for each of these seven periods.     

两万年来的中国多年冻土形成演化

利用大量的古多年冻土遗迹和古冰缘现象,并佐以古冰川、孢粉及动物化石等资料,重建了20ka以来中国多年冻土演化进程.结果表明,在末次冰期最盛期(LGM,或末次多年冻土最大期LPMax),中国多年冻土面积达到了5.3×10^6~5.4×10^6km^2(现今中国多年冻土面积的3倍多),而全新世大暖期(HMP,或末次多年冻土最小期LPMin),中国多年冻土面积曾缩减至0.80×10^6~0.85×10^6km^2(约为现今中国多年冻土面积的50%).按照古冻土遗迹的年代及分布等特征,在确定LGM和HMP两个主要时段的冻土格局基础上,将20ka以来中国多年冻土演化进程划分为7个阶段:晚更新世LGM(20000~10800aBP)多年冻土强烈扩展,达到LPMax;早全新世气候剧变期(10800至8500~7000aBP)多年冻土较稳定但相对缩减阶段;中全新世HMP(8500~7000至4000~3000aBP)多年冻土强烈退化阶段,多年冻土缩减到LPMin;晚全新世新冰期(4000~3000至1000aBP)冻土扩展阶段;晚全新世中世纪暖期(1000~500aBP)多年冻土相对退化阶段;晚全新世小冰期(LIA, 500~100aBP)冻土相对扩展阶段,以及近代升温期(近百年来)多年冻土持续退化阶段.本文重建了各时段内古气候、古地理环境以及多年冻土分布范围和其他特征.     

Biomarker evidence for changes in terrestrial organic matter input into the Yellow Sea mud area during the Holocene

We present lipid biomarker records of two cores(ZY1 and ZY3) from the central South Yellow Sea mud area to investigate the changes in sources and transport processes of the sedimentary organic matter(OM) throughout the Holocene. Based on the analysis of marine biomarker content(SPB(Phytoplankton Biomarker, total content of brassicasterol, dinosterol and C_(37)-alkenones) and crenarchaeol), and terrestrial biomarkers(Sn-alkanols and br GDGTs) as well as TMBR′ and BIT index values, the marine organic matter(MOM) and terrestrial organic matter(TOM) deposition history was reconstructed. Changes in TOM and MOM were related to variations in land vegetation density and marine productivity, as well as transport processes dominated by the oceanic circulation system. The marine biomarker contents from the South Yellow Sea have generally increased throughout the Holocene, indicating that the increased MOM contents were mainly controlled by the strengthening of the circulation system. The terrestrial biomarkers, on the other hand, were more variable, indicating more complex influence of TOM burial in the Yellow Sea. During the Early Holocene(7200–6000 cal yr BP), the moderate TOM input revealed by the terrestrial proxy records may result from abundant land source supply by strong river transport despite the lack of transport via circulation system. The Mid-Holocene(6000–3000 cal yr BP) was characterized by decreased terrestrial biomarker contents. The balance between the decrease in land source supply and increase of transportation by the current system of the TOM resulted in the lower but stable contents of TOM. During the Late Holocene(3000 cal yr BP to present), the TOM deposition in the South Yellow Sea increased as the current system was further enhanced and thus transported more TOM to the central South Yellow Sea, although the land supply of TOM was further reduced.     

Geochemistry and magmatic properties of eruption episodes from Haroharo linear vent zone, Okataina Volcanic Centre, New Zealand during the last 10 kyr

Post-10 ka rhyolitic eruptions from the Haroharo linear vent zone, Okataina Volcanic Centre, have occurred from several simultaneously active vents spread over 12 km. Two of the three eruption episodes have tapped multiple compositionally distinct homogeneous magma batches. Three magmas totalling ~8 km³ were erupted during the 9.5 ka Rotoma episode. The most evolved Rotoma magma (SiO₂=76.5–77.9 wt%, Sr=96–112 ppm) erupted from a southeastern vent, and is characterised by a cummingtonite-dominant mineralogy, a temperature of 739±14°C, and fO₂ of NNO+0.52±0.11. The least evolved (SiO₂=75.0–76.4 wt%, Sr=128–138 ppm, orthopyroxene+ hornblende-dominant) Rotoma magma erupted from several vents, and was hotter (764±18°C) and more reduced (NNO+0.40±0.13). The ~11 km³ Whakatane episode occurred at 5.6 ka and also erupted three magmas, each from a separate vent. The most evolved (SiO₂=73.3–76.2 wt%, Sr=88–100 ppm) Whakatane magma erupted from the southwestern (Makatiti) vent and is cummingtonite-dominant, cool (745±11°C), and reduced (NNO+0.34±0.08). The least evolved (SiO₂=72.8–74.1 wt%, Sr=132–134 ppm) magma was erupted from the northeastern (Pararoa) vent and is characterised by an orthopyroxene+ hornblende-dominant mineralogy, temperature of 764±18°C, and fO₂ of NNO+0.40±0.13. Compositionally intermediate magmas were erupted during the Rotoma and Whakatane episodes are likely to be hybrids. A single ~13 km³ magma erupted during the intervening 8.1 ka Mamaku episode was relatively homogeneous in composition (SiO₂=76.1–76.8 wt%, Sr=104–112 ppm), temperature (736±18°C), and oxygen fugacity (NNO+0.19±0.12). Some of the vents tapped a single magma while others tapped several. Deposit stratigraphy suggests that the eruptions alternated between magmas, which were often simultaneously erupted from separate vents. Both effusive and explosive activity alternated, but was predominantly effusive (>75% erupted as lava domes and flows). The plumbing systems which fed the vents are inferred to be complex, with magma experiencing different conditions in the conduits. As the eruption of several magmas was essentially concurrent, the episodes were likely triggered by a common event such as magmatic intrusion or seismic disturbance.     

Evolution of the Juan Fernandez microplate during the last three million years

During the spring of 1983, the R/V “Thomas Washington” surveyed an area located north of the Antarctic-Nazca-Pacific triple junction at 35°S.Magnetic and SEABEAM bathymetric data collected during the survey confirmed the existence of the Juan Fernandez microplate. This paper presents an analysis of the magnetic anomaly data.The western boundary of the microplate is a fast spreading center which has existed since 2 Ma and where the accretion rate has been about 14.5 cm/yr for the last 0.7 Ma.The eastern boundary of the microplate is characterized by a slow spreading center which separates the Juan Fernandez and Nazca plates. The accretion rate has been about 7.0 cm/yr between 0.7 and 0.4 Ma and about 1.6 cm/yr for the last 0.4 Ma.The two spreading centers are connected in the north and south by transform faults.Between the Juan Fernandez and Rapanui microplates, the East Pacific Rise is well defined between 30 and 32°S. In this region the axis displays a record accretion of about 17.2 cm/yr.South of the Juan Fernandez microplate, one magnetic profile (Oceano 7008) indicates that the opening rate is about 12.0 cm/yr on the Antarctic-Pacific ridge.The birth of the microplate is dated at about 2 Ma when the western boundary started to accrete. The evolution of the microplate corresponds to a transfer of accretion from the eastern boundary to the western axis. This is revealed by the net decrease of the opening rate from 7.0 cm/yr to 1.6 cm/yr observed at the eastern ridge where a small jump occurred at 0.4 Ma.     

Major ash eruptions of Barren Island volcano (Andaman Sea) during the past 72 kyr: clues from a sediment core record

Barren Island (Andaman Sea) is the northernmost active volcano of the Indonesian Arc. To construct the eruptive history of this little studied volcano, we measured ¹⁴C dates of inorganic carbon in sediment beds, and Sr and Nd isotopic ratios of seven discrete ash layers, in a marine sediment core collected from 32 km southeast of the volcano. The study reveals that the volcano had seven major ash eruptions at ~70, 69, 61, 24, 19, 15, and 10 ka. The ash layers erupted from 70 ka through 19 ka have highly uniform Nd isotopic composition, and since the ~15 ka eruption to the present the isotopic composition has been highly variable. Between ~24 ka and ~10 ka, the volcano had large ash eruptions spaced at 4,500 year intervals. Isotopically correlating the precaldera lavas and ash exposed on the volcano to the uppermost ash layer in the core, we infer that the caldera of Barren Island volcano is younger than 10 ka.     

Geochemical evidence for non-marine depositional environment of foraminiferal fossils from the Nihewan Basin, China

From the first finding in 1970s, the findings of foraminiferal fossil assemblages in inland basins have been reported from time to time, especially in recent years. The debates on the depositional environment of foraminiferal fossils have become the hot spot of researches again in China. Based on the researches of trace element geochemistry and electron scanning microscope of shells of Quaternary foraminiferal fossils from the Xiaodukou section in the inland Nihewan basin, the original ⁸⁷Sr/⁸⁶Sr and other geochemical information of shells were believed to be preserved well and could be used to rebuild the geochemistry of contemporary waters where foraminifera deposited, although there existed some effects of burial diagenesis on the geochemistry of shells to a certain extent. The ⁸⁷Sr/⁸⁶Sr ratios of well-preserved Xiaodukou foraminiferal shells were measured, giving a range of 0.711190±25–0.712018±14, apparently higher than the value of contemporary seawater (0.709087–0.709147) and similar to that of the Sanggan River, proving that it represented the value of the ancient lacustrine water. The hyperbolic mixing models of ⁸⁷Sr/⁸⁶Sr-palaeosalinity and ⁸⁷Sr/⁸⁶Sr-Sr/Ca indicated that the contemporary waters where Xiaodukou foraminifera inhabited was an inland lake and there was no seawater input to the depositional environment.     

Geospatial-temporal analysis of land-use changes in the Yellow River Delta during the last 40 years

Research on land use/land cover changes (LUCC)has been the core project of the Global EnvironmentalChanges since the 1990s[1—6]. Scientists at home andabroad have been laying emphasis on integrationstudies on land-use change by “space and process”features[7—10] as researches on LUCC are in a greatdeal. It is of paramount important for us to studyLUCC at various spatial-temporal scales and build aquantitative assessment of land-use conversion by in-tegrated spatial-temporal features. …     

Evolution of radiative sand ridge field of the South Yellow Sea and its sedimentary characteristics

A sand ridge field of 22 470 km² consists of fine sands and silts originally from the old Changjiang River sediment during the late Pleistocene period. Late Holocene sand stratum with its well-preserved larmnary bedding of more clay particles reflects the influence from the Yellow River. There are three genetic types of morphology of sand ridge field as follows: (i) reformed alluvial sandy bodies and old river valleys, located in the central and southern parts, formed from the end of Pleistocene to the present. (ii) Radiative current ridges and patrimonal valley type, located in the northeastern part, formed during the early or middle Holocene time. (iii) Eroded-depositional sandy bodies in the north and outer parts, and erosional trough in the north formed since the middle Holocene transgression. The sand ridge field has a periodic nature of developing processes: the period of sediment accumulation by rivers during cold epoch with low sea level and the period of erosional formation by tidal currents during warm epoch of transgression. The river-sea interactive process in the area is closely related to the climate change; the rising and falling of the sea level is the detonating agent of the coast zone land-sea dynamic interactive processes. They can be summarized as “transgression-dynamic-sedimentation” processes. Project supported by the National Natural Science Foundation of China (Grant No. 49236120). Pmject codmg: SCIEL 21198103.     

The evolution of the Kuroshio Current over the last 5 million years since the Pliocene: Evidence from planktonic foraminiferal faunas

Meridional heat transport of the western Pacific boundary current (the Kuroshio Current) is one of the key factors in global climate change. This current is important because it controls the temperature gradient between low latitudes and the North Pacific and so significantly influences mid-latitude atmosphere-ocean interactions. Here we reconstruct changes in hydrological conditions within the mid-latitude mainstream of the Kuroshio Current based on faunal analysis of planktonic foraminifera in core DSDP 296 from the Northwest Pacific Ocean. This approach enabled us to deduce evolutionary processes within the Kuroshio Current since the Pliocene. A total of 57 species in the coarser section (>150 µim) were identified; results indicate that planktonic foraminiferal faunal evolution has mainly been characterized by three major stages, the first of which comprised mixed-layer warm-water species of Globigerinoides ruber which first appeared between 3.5 and 2.7 Ma and then gradually increased in content. Percentages of another warm-water species of G. conglobatus also gradually increased in number over this interval. Variations in warm-water species indicate a gradual rise in sea surface temperature (SST) and imply initiation of Kuroshio Current impact on the Northwest Pacific Ocean since at least 3.5 Ma. Secondly, over the period between 2.7 and 2.0 Ma, thermocline species of Globigerina calida, Neogloboquadrina humersa, Neogloboquadrina dutertrei, and Pulleniatina obliquiloculata started to appear in the section. This fauna was dominated by G. ruber as well as increasing G. conglobatus contents. These features imply a further rise in SST and its gradually enhanced influence on thermocline water, suggesting strengthening of the Kuroshio Current since 2.7 Ma. Thirdly, between 2.0 Ma and present, increasing contents of thermocline species (i.e., G. calida, N. dutertrei and P. obliquiloculata) indicate a gradual rise in seawater temperature at this depth and also imply more intensive Kuroshio Current during this period. On the basis of comparative records from cores ODP 806 and DSDP 292 from the low latitude Western Pacific, we propose that initiation of the impact of the Kuroshio Current in the Northwest Pacific and it subsequent stepwise intensifications since 3.5 Ma can be closely related to the closure and restriction of the Indonesian and Central American seaways as well as variations in the Western Pacific Warm Pool (WPWP) and equatorial Pacific region.

     

Molecular biomarker record of paleooceanographic environment in the East China Sea during the last 35000 years

By reference of the δ¹⁸O and δ¹³C isotopic compositions of G.sacculifer and accelerator mass spectrometry (AMS)¹⁴C dates, the U _K ³⁷ , ∑C _– ²¹ /∑C _+- ²² and Pr/Pn in core DGKS9603 have been used to characterize the changes of paleooceanographic environment occurring in the East China Sea (ECS) during the last 35000 years. The stratigraphic records of these proxies have shown that during the last 35 ka the Okinawa Trough has gone through 7 stronger cold-climate events (C₁–C₇) and 9 terrigenous matter-decreasing events (e₂–e₉), of which, the C₁ corresponds to the cold episode occurring in the middle late Holocene, C₂–C₄ and C₇ correspond to the H₁–H₄ events, respectively. e₁ and e₃–e₈ correspond to the decrease of sea surface temperature (SST), respectively. The terrigenous inputs increased when Heinrich events occurred. Climate colding resulted in the decrease of terrigenous matter transported by rivers, and the increase of that transported by winter monsoon. Heinrich events are closely related to East Asia monsoon. During the Last Glacial Maximum (LGM, 15.5–25.8 Cal ka BP), reduction environment fluctuated strongly, bringing forth three stronger reduction events (R₁–R₃) and one weaker reduction event (O), of which, R₁–R₃ correspond to the decrease of SST and increase of terrigenous nutrient and O corresponds to the decrease of terrigenous nutrient. The fluctuation of reduction condition must be related to the change of sea surface productivity.     

The oxygen isotopic composition and temperature of Southern Ocean bottom waters during the last glacial maximum

We provide two new determinations of the oxygen isotopic composition of seawater during the last glacial maximum (LGM). High-resolution oxygen isotopic measurements were made on interstitial waters from Ocean Drilling Program (ODP) Sites 1168 and 1170 in the southeast Indian Ocean sector of the Southern Ocean. We use a diffusion-advection numerical model to calculate the glacial-interglacial change in bottom-water δ¹⁸O_sw from the pore water δ¹⁸O profiles; the first such determinations from this part of the oceans. Statistical analyses of the model runs indicate that Circumpolar Deep Water (CDW) δ¹⁸O_sw changed by 1.0-1.1±0.15‰ since the last glacial maximum (LGM). Our results are consistent with a previous calculation from a South Atlantic Southern Ocean location (ODP Site 1093) also situated within CDW. The new values determined in this study, together with previous estimates, are converging on a global average Δδ¹⁸O_sw of 1.0-1.1‰.Using the calculated bottom-water δ¹⁸O_sw, we have extracted the temperature component from the benthic foraminiferal δ¹⁸O record at Sites 1168 and 1170. Since the LGM, bottom waters at these two sites warmed by 2.6 and 1.9°C, respectively. The absolute temperature estimates for the LGM (−0.5°C [Θ=−0.6°C] at Site 1168 and −0.2°C [Θ=−0.4°C] at Site 1170) are slightly warmer than those reported from previous studies using the same technique, but are consistent with more homogenous deep-ocean temperatures during the LGM relative to the modern.     

Paleoceanographical records under impact of the Indian monsoon from the Bengal Deep Sea Fan and Ninetyeast Ridge during the last 260 ka

The orbital and interior climatic cycles can be found both in the Bengal Deep Sea Fan and Ninetyeast Ridge, North Indian Ocean. The periodicity of the Quaternary glacio-eustacy by 100 ka gave a strong impact on the sedimentation in the fan area and the monsoon signals controlled by the obliquity and precession were easily picked up. This paper discusses the possible correlation between the environmental elements on the basis of the ETP phase wheels. A rapid change with short-periods develops during the past 60 ka in the region under study as well. The variability of paleoproductivity has a nonlinear response to the Indian summer monsoon. As contrasted to the Northwest Indian Ocean, here an abundance ofGlobigerina bulloides, a proxy to indicate upwelling current, does not imply so much a promotion of the summer monsoon as its decrease. The record from the ridge area shows in a longer-scale a climatic evolutionary feature corresponding to that of the fan area. A special and great event arising at around 165 kaBP and meaning a catastrophe for ecological environment is reported in this paper. It is also regarded as a result induced by the monsoon.     

近1200 a来黄河下游梁山泊沉积记录的环境变迁

利用梁山泊670 cm柱状岩芯沉积物,基于精确的AMS-~(14)C年代测定,通过高分辨率的粒度、磁化率、总有机碳、C/N比值等环境代用指标的综合分析,并结合历史文献记载,初步揭示了1200 a来黄河下游地区平原湖泊沉积特征及环境演化历史.结果表明,梁山泊环境演化大致分为5个阶段:790-940 AD期间,为低湖面的沼泽沉积环境,气候冷干;940-1215 AD期间,屡次受到黄河决溢洪水影响,湖盆扩张,湖泊水位上升,为梁山泊极盛期,气候暖湿;1215-1310 AD期间,黄河夺淮入黄海,湖区淤积严重,湖泊萎缩减小;1310-1470 AD期间,再次受到黄河决溢洪水影响,水位上升,面积扩张,但逊于极盛期;1470 AD至现代,黄河河道进一步南移,远离梁山泊,湖盆淤积抬高,梁山泊最终消失,直到1855AD,黄河第6次大改道北移,湖泊再次受到黄河洪水影响,由于前期受到泥沙淤积抬高,该地区仅作为黄河泥沙承载区.在气候变化大背景下,黄河改道决溢是梁山泊演化的主因.