南海北部陆丰凹陷中新世底栖有孔虫组合与古环境演化研究

The Miocene epoch marks the most crucial period during the Cenozoic cooling trend, characterized by the Middle Miocene Climatic Optimum(MMCO) and a series of short–lived cooling events(Miocene isotope events).To understand the paleoenvironmental evolution along the shallow water shelf in the South China Sea during the Miocene, the benthic foraminiferal assemblage and total organic carbon content(TOC) were analyzed at Hole LF14 located in the Lufeng Sag, northern South China Sea. Three benthic foraminiferal assemblages(e.g., the Uvigerina spp. assemblage, the Cibicides spp. assemblage, and the Cibicidoides spp. assemblage), corresponding to different watermass conditions, were recognized based on Q–mode factor analysis. Early studies suggested that Hole LF14 was deposited under semienclosed bay, middle to outer shelf or even upper bathyal environment during ～18.7–4.53 Ma. The dominant Uvigerina spp. assemblage was characterized by low diversity and shallow infaunal to infaunal species, indicating a warm, low–oxygenation and eutrophic conditions since the Early Miocene to MMCO(～18.7–14.24 Ma). An abrupt sea level drop and significant faunal changes were recorded during 14.24–13.41 Ma, suggesting development of the East Antarctic Ice Sheets, which resulted in a drop of sea level and change in benthic foraminiferal assemblages along the shallow water shelf. Beyond the Uvigerina spp.assemblage, the Cibicides spp. assemblage became important during the middle–late Middle Miocene(14.24–11.54 Ma). This assemblage was dominated by epifaunal species with relative high diversity, suggesting high–energy, high–oxygenation and oligotrophic conditions with episodic supply of organic food. The dominant Cibicidoides spp. assemblage with high diversity, indicates a mesotrophic conditions with relative high–oxygen content during the Late Miocene to Pliocene(11.54–4.53 Ma). The appearance and continuous occurrence of Ammonia spp. and Pseudorotalia spp. since 10.02 Ma, may reflect the influence of the Kuroshio Current.     

Sea surface temperature variations in the southwestern South China Sea over the past 160 ka

Sea surface temperatures (SSTs) in the southwestern South China Sea have been reconstructed for the past 160 ka using the Uk37 paleothermometer from the core MD01-2392. The temperature differences between glacial times (MISs 6 and 2) and interglacial times (MISs 5.5 and 1) are 2.2~2.5 ℃. Younger Dryas event during the last deglaciation was documented in both the planktonic foraminiferal δ18O and SST records. After MIS 5.5, SSTs displayed a progressive cooling from 28.6 to 24.5 ℃, culminating at the LGM. During this gradual cooling period, warm events such as MISs 5.3, 5.1 and 3 were also clearly documented. By comparison of SST between the study core and Core 17954, a pattern of low or no meridional SST gradients during the interglacial periods and high meridional SST gradients during the glacial periods was exhibited. This pattern indicates the much stronger East Asian winter monsoon at the glacial than at the interglacial periods. Spectral analysis gives two prominent cycles: 41 and 23 ka, with the former more pronounced, suggesting that SSTs in the southern SCS varied in concert with high-latitude processes through the connection of East Asian winter monsoon.     

Application of biologic silicon in modern sedimentary section to reconstruction of phytoplankton changes in the East China Sea and the Huanghai Sea during last 200 years

Biomarkers had been widely used to reconstruct phytoplankton productivity,and this method was applied in the East China Sea and the Huanghai Sea (Yellow Sea).In this study,Biologic Silicon (BSi) was used as productivity proxy to reconstruct productivity change of phytoplankton during last 200 years.The results show that the BSi contents of surficial sediments were in the range of 0.018%-2.516%,averaging 0.726%,and had a similar variation trend with phytoplankton biomass.The vertical distribution profiles revealed that BSi contents were relatively stable,in accordance with the variations of the contemporary phytoplankton standing crop index.According to the stability analysis of BSi in sediments,BSi was not degradaded for the past two hundred years and remained in sediments steadily.Thus,BSi in sediments had the potential to invert paleoproductivity.To conduct further survey,the linear regression equation between BSi contents and phytoplankton biomass index could be used to calculate the phytoplankton productivity by BSi,so that paleoproductivity may be reconstructed during last 200 years.     

Seasonal variations of particulate silicon in the Changjiang (Yangtze River) Estuary and its adjacent area

Temporal and spatial distribution of biogenic (BSi) and lithogenic (LSi) silica were studied in the Changjiang (Yangtze River) Estuary and its adjacent area. The annual average BSi and LSi concentrations were (1.71 ± 1.79) μmol/L and (0.56 ± 1.41) mmol/L, respectively. Both BSi and LSi were high in the inshore areas, where they received terrigenous discharge from the Changjiang, and decreased towards the offshore region. BSi and LSi were most abundant at the near bottom layer due to the high sedimentation rates and resuspension of sediment. Diatom blooms occurred in summer with high Chl a concentration in the surface layer, which induced that BSi in the surface layer during summer was obviously higher than that in the surface layer of other seasons. LSi concentration was maximal in autumn and spring and minimum in summer, associated with the seasonal variation of SPM values. Drifting investigation and mesocosm experiments were conducted during dinoflagellate bloom, aiming to understand the effect of nutrients on BSi by changing the phytoplankton composition. The results show that the low dissolved inorganic phosphorus concentration and high molar ratio of N/P (dissolved inorganic nitrogen vs. dissolved inorganic phosphorus), were the important factors for decreasing diatom biomass in the study area, and it would subsequently decrease the BSi concentration in aquatic ecosystem.     

南黄海生物硅的时空变化

Concentrations of biogenic silica(BSi) in the southern Yellow Sea were determined during four cruises(spring:April–May 2014; autumn: November 2014; summer: August–September 2015; winter: January 2016). Samples of BSi were measured using the double extraction method. Seasonal and spatial variations of BSi and the potential correlation between chlorophyll a(Chl a) content and BSi in four seasons were measured in this study. Significant spatial variability was observed in seawater BSi concentrations. The average concentration of BSi was highest in winter and lowest in spring. Furthermore, the relationships between concentrations of BSi and hydrological parameters were also discussed. There was a significant positive correlation between Chl a and BSi. The concentrations of BSi showed significant relationships with temperature and the concentrations of silicates, total inorganic nitrogen and total inorganic phosphorus, indicating that distribution of BSi was affected by temperature and nutrient level.     

The long-term variability of sea surface temperature in the seas east of China in the past 40 a

The global surface temperature change since the mid-19th century has caused general concern and intensive study. However, long-term changes in the marginal seas, including the seas east of China, are not well understood because long-term observations are sparse and, even when they exist, they are over limited areas. Preliminary results on the long-term variability of sea surface temperature (SST) in summer and winter in the seas east of China during the period of 1957-2001 are reported using the Ocean Science Database of Institute of Oceanology, Chinese Academy of Sciences, the coastal hydrological station in situ and satellite data. The results show well-defined warming trends in the study area. However warming and cooling trends vary from decade to decade, with steady and rapid warming trends after the 1980s and complicated spatial patterns. The distribution of SST variation is intricate and more blurred in the areas far away from the Kuroshio system. Both historical and satellite data sets show significant warming trends after 1985. The warming trends are larger and spread to wider areas in winter than in summer, which means decrease in the seasonal cycle of SST probably linked with recently observed increase of the tropical zooplankton species in the region. Spatial structures of the SST trends are roughly consistent with the circulation pattern especially in winter when the meridional SST gradients are larger, suggesting that a horizontal advection may play an important role in the long-term SST variability in winter.     

Paleoenvironmental records from the northern South China Sea since the Last Glacial Maximum

Core ZHS-176 contains the paleoenvironmental records from the northern South China Sea (NSCS) since the Last Glacial Maximum (LGM). A coupled approach based on clay mineral assemblages, planktonic foraminiferal oxygen and carbon isotopes, and calcium carbonate content is used to trace the sources of the fine-grained sediment and to investigate the paleoenviornmental evolution in this area. Clay mineral assemblages are dominated by illite (average about 39%) and chlorite (about 27%), which comes mainly from Taiwan and the East China Sea. Kaolinite, which accounts for about 13%, comes mainly from the Zhujiang (Pearl) River, and Luzon Island is the main source for smectite (about 21%). The planktonic foraminiferal oxygen isotopic oscillations during the last glacial period are coeval with climate variations recorded in the Greenland ice core and Western Pacific sediment. These variations include the LGM, Heinrich event 1, Bφlling-Allerφd (B/A), and Younger Dryas. For the Holocene, three periods of strong precipitation (S1-S3) and three periods of weak precipitation (W1-W3) are identified. The oxygen isotopic record exhibits corre-lation with climate records from distant regions, including the high-latitude Northern Hemisphere, providing evidence for global tele-connection among regional climate. A brief, negative planktonic foraminiferal carbon isotopic excursion during B/A reflects increased methane released from marine gas hydrate due to the rapid warming of the water. By comparing calcium carbonate content curves of the core ZHS-176 with these of other five boreholes lying above the lysocline, a remarkable low calcium carbonate event is found during the early Holocene in NSCS.     

中国东海和南黄海沿海平原MIS 3晚期海侵层的动力模拟研究

Abundant evidences of higher sea levels from Jiangsu and Fujian coasts have proved a marine transgression event during 30–40 ka BP, suggesting that there was a stage with high sea level and a warm climate when ice sheets shrank in the Northern Hemisphere. The duration of 30–40 ka BP spanned a period in the late Marine Isotope Stage 3(MIS 3) and was in nature an interstadial epoch during the Last Glacial period of the Quaternary. Different from the glacial period with a cold climate, this marine transgression considered as a penultimate higher sea level during the Quaternary remains a puzzle that why the evidence is contrary to the Quaternary glacial theory. It is important to understand sea level rise for these areas sensitively responding to the global changes in the future. To recognize the key issues on sea level changes, the eustatic sea level(H_S) was defined as the glaciation-climateforced sea levels, and the relative sea level change(H_R) was defined as that a sea level record was preserved in sediment that experienced multiple secondary actions of land and sea effects. On the basis as defined above, we constructed multi-level models of climate-driven glacio-eustatic changes and land-sea systems. By integrating data sets from eight borehole cores and prescribing the boundary conditions, we simulated the changes of HS and HR in the East China Sea and southern Yellow Sea areas in the late MIS 3. The marine transgression strata from the borehole core data was identified at ca. 30 m below present sea level as a result of the collective influence of ice melting water, neotectonic subsidence, sediment compaction and terrestrial sediment filling since ca. 35 ka ago,whereas the simulated relative sea-levels turned out to be –26.3––29.9 m a.s.l. The small error involved in the simulation results of ±(2.5–4.5) m demonstrated the credibility of the results. Our results indicated that sea level change in the late MIS 3 was dominated by glacial effects, in which the eustatic sea-level was between –19.2––22.1m a.s.l. The study sheds light on the nature of sea-level changes along the east coast of China in the late MIS 3 and contributes to understanding the characteristics of marine transgression under the effects of multiple complex land-sea interactions.     

春季北大西洋涛动与夏季西北太平洋热带气旋生成频数关系的年代际变化

The present study reveals the fact that the relationship between the spring(April–May) North Atlantic Oscillation(NAO) and the following summer(June–September) tropical cyclone(TC) genesis frequency over the western North Pacific(WNP) during the period of 1950–2018 was not stationary. It is shown that the relationship between the two has experienced a pronounced interdecadal shift, being weak and insignificant before yet strong and statistically significant after the early 1980 s. Next we compare the spring NAO associated dynamic and thermodynamic conditions, sea surface temperature(SST) anomalies, and atmospheric circulation processes between the two subperiods of 1954–1976 and 1996–2018, so as to illucidate the possible mechanism for this interdecadal variation in the NAO-TC connection. During the latter epoch, when the spring NAO was positive,enhanced low-level vorticity, reduced vertical zonal wind shear, intensified vertical velocity and increased middle-level relative humidity were present over the WNP in the summer, which is conducive to the genesis of WNP TCs. When the spring NAO is negative, the dynamic and thermodynamic factors are disadvantageous for the summertime TC formation and development over the WNP. The results of further analysis indicate that the persistence of North Atlantic tri-pole SST anomalies from spring to the subsequent summer induced by the spring NAO plays a fundamental role in the linkage between the spring NAO and summer atmospheric circulation.During the period of 1996–2018, a remarkable eastward propagating wave-train occurred across the northern Eurasian continent, forced by the anomalous SST tri-pole in the North Atlantic. The East Asian jet flow became greatly intensified, and the deep convection in the tropics was further enhanced via the changes of the local Hadley circulation, corresponding to a positive spring NAO. During the former epoch, the spring NAO-induced tri-pole SST anomalies in the North Atlantic were non-existent, and the related atmospheric circulation anomalies were extremely weak, thereby leading to the linkage between spring NAO and WNP TC genesis frequency in the following summer being insignificant.     

Long-term changes in sea surface temperature(SST) within the southern Levantine Basin

Knowledge of sea surface temperature(SST) behaviour is vital for long-term climate scenarios. This study highlights essential outcomes about the distinguishable and unsurprising warming of the SST along the southern border of the Levantine Basin. The analysis is based on monthly SST data for the period 1948–2018. The southern Levantine Basin has undergone SST increase, during the last 71 years. In this study, a consistent warming trend has been found for the analysed SST data series, with a rate of 0.04°C/a, i.e., 0.4°C/(10 a). From 1975 to 1991 the mean annual SST was 17.1°C, and this increased to be 19.2°C, over the period 2002–2018. Results revealed two opposite trends of variability: a decreasing trend(–0.06°C/a) over the period 1975–1991, and an increasing trend(0.2°C/a) from 2002 to 2018. Over the period 1948–2018, positive mean annual SST anomalies had an average of1.8°C, and negative anomalies had an average of –1.1°C. The lowest SST total increase was found from January to April, with values about 0.03°C, while the highest warming appeared from June to September. The driving mechanisms behind the SST changes need to be more investigated, to understand the future trends and impacts of climate change in the Levantine Basin.     

东海、黄海近代沉积物中生物硅含量的分布及其反演潜力

以东海、黄海2006年4月、10月航次采集的沉积物样品为研究对象,结合沉积物中生物硅(BSi)含量的空间分布特征进而讨论BSi的反演潜力。研究发现,调查海域表层沉积物中BSi的含量介于0.018%~2.516%,平均值为0.726%,柱状沉积物中BSi的含量波动较小,相对稳定。整体而言BSi含量与相应年代的浮游植物现存量变化的趋势相近。经一元线性分析发现BSi含量与硅藻生物量的相关性显著。为进一步证实由BSi含量反演古生产力的有效性和可信度,采用Tun-nicliffe等的方法探讨了BSi含量在沉积物中的稳定性,调查结果表明,近150 a来BSi几乎没有降解,能够稳定地保存于沉积物中。综上可以初步判断沉积物中BSi含量可作为古生产力指标来反演古生产力的潜力。     

台湾东部黑潮区海源碳的沉积物记录与近千年来生产力与气候变化的反演

本文基于对台湾以东黑潮主流区沉积物的粒度和定年，通过解析沉积物总有机碳及其同位素组成获取海源碳变化特征，首次报道了该海区近千年来的初级生产力与气候变化反演结果。研究显示，台湾以东黑潮主流区近千年来的平均沉积速率为34.44 cm/ka，沉积环境较为稳定。另外，台湾以东黑潮主流区沉积物中的总有机碳和总氮含量主要受台湾东部河流输入、海洋初级生产力的沉降过程、成岩作用和粒度效应影响。对沉积物海源碳的定量估算表明，近千年来台湾以东黑潮主流区沉积物中40.02%~73.88%的有机质为海源输入，陆源输送次之。同时，近千年来台湾以东黑潮主流区沉积物记录较好地反映了中世纪暖期、小冰期和现代暖期3个气候变化阶段。1150-1420年期间，沉积物中总有机碳、总氮和海源碳含量缓慢升高，较高的表层海水温度有利于海洋初级生产力水平的升高。1500-1840年期间，较低的表层海水温度和亚洲大陆风尘输送水平使得海洋初级生产力较低，同时台湾地区小冰期较高的降水量有利于台湾东部河流向海输送，增强的水动力条件可能会加强海底沉积物的东移，从而导致该区域沉积物中总有机碳含量的增加。进入现代暖期以来研究区的海水温度逐渐增暖，而东亚季风强度和降水量却表现出波动的年际变化特征，并体现在研究区1930-1950年和1970年期间沉积物的中值粒径、总有机碳和总氮含量的快速波动。     

Millennium scale environment changes of the Okhotsk Sea during last 80 kyr and their phase relationship with global climate changes

The paper presents the records of several paleoproductivity proxies (PP) (biogenic opal and Ba (Si_bio, Ba_bio), organic carbon (C_org) and carbonate Ca_carb, chlorin and benthic foraminifera abundance (BFA)) in sediments of the Okhotsk Sea for the last 80 kyr with a resolution of ∼100–300 years. The sediment age model was based on the AMS ¹⁴C data, records of benthic foraminifera δ¹⁸O, paleointensity of the Earth’s geomagnetic field and magnetic susceptibility. PP values demonstrate series of severe prolonged productivity drops in the Okhotsk Sea followed by a sharp increase during the last glaciation. On the basis of quantitative estimations of the paleoproductivity in the Okhotsk Sea during the cold MIS 2 and warm Holocene (Gorbarenko and Goldberg, 2005), it is suggested that the millennium scale relationship in productivity-climate changes of this basin was similar: an increase in the sea’s productivity was related with regional climate warming and vice-versa. The PP records of productivity/climate oscillations in the Okhotsk Sea during MIS 2–4 occurred contemporaneously with the North Atlantic cold Heinrich events (HE) and Greenland Dansgaard-Oyeshger interstadial (DOI). Observed successions of prolonged climate cooling events followed by rapid, abrupt warming are similar to climate and environmental oscillations in the N. Atlantic and Greenland, that confirms the millennium-scale climate changes synchronicities in the Northern Hemisphere including the far NW Pacific, the hydrology and climate conditions of which are close to those of the Okhotsk Sea. Synchronism of the N. Hemisphere severe cooling (including the Okhotsk Sea) with the Antarctic warming suggests that mechanisms of the “seesaw” effect (Blunier and Brook, 2001) in the low latitude heat redistribution between high latitudes of both hemispheres were more complicated than direct NADW formation forcing and encompasses the global atmospheric reorganization. Within the PP used a closer connection in the Okhotsk Sea millennium oscillations was observed for the C_org, BFA and chlorin; Ba_bio increases more closely to DOI. Si_bio variability does not show any evident correlation with productivity changes.     

华北地区夏季降雨量与南海海温长期变化的关系

比较了华北地区7个站与17个站1951-1997年夏季（6，7，8月）降雨量与气候随时间的变化特征，并对其成因作了探讨。结果表明，用北京、天津、邢台、烟台、郑州、太原和济南等7个站可代表该地区夏季降雨量与气候的多尺度变化特征，过去47a该地区依次经历了湿凉、湿热、湿凉、干热、湿热几个时期，降雨量的长期变化与南海前冬（1-2月）海温成负相关。前冬南海海温偏高，意味着初夏南海地区大气对流低频振动偏弱，南海夏季风爆发较晚，西南季风较弱，夏季西太平洋副高位置偏南，华北地区大气低层北风加强，华北地区夏季少雨，前冬南海海温偏低时情况则相反，考虑冬季（1-2月）南海南温和7-8月西太平洋副高脊线位置（纬度）的影响用均生函数建模，试验结果与用子波变换重构方法考虑华北地区夏季降雨量的变化趋势比较，二者相吻合，预测试验结果与过去3a的实况基本一致。     

渤海颗粒有机碳与生物硅的分布及来源

海洋碳、硅循环及其相关联的生物地球化学过程是全球环境变化的热点问题,也是海洋科学关心的重要领域。利用2012年5月和11月份对渤海海域的调查结果,对该海域颗粒有机碳和生物硅的分布特征及来源进行了讨论。主要结论为:渤海有机碳以溶解有机碳为主,具有春季高和秋季低的特征;由陆地来源和海洋自生的有机碳组成,且以海洋来源的有机碳为主。渤海生物硅分布具有明显的梯度特征,河流输入同样对其含量的影响较为突出。渤海沉积物中生物硅含量较高,明显高于中国东部陆架海。渤海表层沉积物中生物硅主要是海源的,依次由浮游藻类、植硅体和海绵骨针所构成,其中浮游藻类占62.9%,陆源植硅体占31.1%。渤海沉积物发现了来自于草本植物的植硅体,这说明了陆地产生的植硅体对海洋生物硅的贡献。     

Paleoenvironment changes in the NW Okhotsk Sea for the last 18 kyr determined with micropaleontological,geochemical, and lithological data

Lithological, geochemical, and micropaleontological data indicate that the Late Glacial of the northwestern Okhotsk Sea (OS) is characterised by severe climatic and environmental conditions with mainly perennial sea ice coverage and low productivity accompanied by weak deep-water ventilation and a temperate formation of the upper Sea of Okhotsk Intermediate Water (SOIW). The age model of the studied core sediments was constructed by AMS ¹⁴C dating. The most severe environmental conditions occurred during the period 15.8–14.8 kyr, synchronous with cold Heinrich event 1. Insignificant regional environmental amelioration accompanied by an increase of productivity and ice weakening during summer occurred almost simultaneously with the Bølling–Allerøed (BA) warming. The obtained results distinguished both the Bølling and Allerøed warmings as having different environmental conditions. Oxygen content in the surface sediment was low, as seen from the production of the benthic foraminifera (BF) species. During 12.6–11.1 kyr, synchronous with the Younger Dryas (YD) cold event, the regional environment conditions were cold, but not as severe as the glacial ones. Some climatic warming since the Preboreal has stimulated sea ice melting and surface amelioration during the summer season, which in turn led to a productivity rise and changes in the water column and bottom environment. Some increase in the surface water stratification and the intensified oceanic diatom and surface radiolarian production is parallel with the development of a mesopelagic regime of productivity. The surface sediment condition favours BF abundance and domination by BF species tolerant to oxygen deficiencies. During the Boreal period more stable surface conditions were accompanied by continuously high productivity and an intensifying of its mesopelagic regime.Significant regional climate warming since the Atlantic (9 kyr ago) strongly intensified the summer sea ice melting in the OS, and this created considerable surface environment amelioration with the preferential transport of bacteria and phytodetritus into the SOIW. Further considerable warming of the regional climate from 6 kyr ago contributed to slight sea ice changes, surface water warming, and the enhancement of its stratification; all typical for most of the OS. Along with a high nutrient supply from the Amur River, the NW OS experienced a strong diatom production increase with the maximum amount occurring during the last 3.6 kyr. This changed the productivity type and organic matter export into the water column while increasing the feeding of the “productive” Plagoniidae spp. group and decreasing the microbial biomass supply into the upper SOIW. Some sea surface water cooling or saltier conditions at the beginning of the Subatlantic (2.4–1.8 kyr) was followed by its warming or freshening 1.5–1.0 kyr ago, which likely correlated with the Medieval Warm Period. In turn, that probably led to strong surface water stratification, productivity deterioration and considerable changes in the overall NW OS environment. The established sequence of the northwestern OS environmental changes during the Late Glacial–Holocene is related to the Northern Hemispheric climate changes and was likely forced by atmospheric teleconnection in line with the polar circulation index variability.