A better understanding of how the vertical profile of suspended sediment concentration (SSC) is influenced by multiple factors is required to better understand the hydrodynamics and sediment dynamics of estuaries. Based on in situ measurements obtained during a spring-neap cycle in the estuarine turbidity maximum (ETM) of the Changjiang Estuary in January 2015, we investigate the intratidal evolution and controlling mechanisms of SSC profiles. The results show that during the dry season the ETM was characterized by periodic salinity stratification, low SSC, suspended sediments with reduced grain size, and low sediment availability for resuspension. Three types of SSC profiles were identified, i.e., profiles with two-layer, linear and quasi-uniform structures. The shapes of the SSC profiles varied with time and generally deviated from the equilibrium profile due to the highly variable hydrodynamic and sediment conditions. During ebbs of spring and intermediate tides, the SSC profiles generally evolved from a two-layer to a quasi-uniform structure via a linear structure. Analysis shows that the linear and quasi-uniform profiles occurred under the combination of vertically well-mixed salinity, negligible resuspension, low settling velocity associated with very fine grains, and shallow water depth. Such an evolution pattern can be well reproduced using a one-dimensional numerical model, with the diffusion coefficient being parabolically distributed in the water column and the four factors mentioned above. The findings reported here imply a high variability of SSC profiles in estuarine environments.

Extreme flood events can significantly disturb hydro-sediment dynamics and affect turbidity maximum zone (TMZ) distributions, which are crucial to estuary evolution. This study used field data and eight Sentinel-2A/B MSI, GF-1/6 WFV, and Landsat-8 OLI satellite images to examine the behavior of the TMZ in the North Passage (NP) and South Passage (SP) of the Yangtze Estuary under the influence of the 2020 extreme flood event. Images covered average annual, usual flood, and extreme flood (river discharge above 70,000 m3/s) conditions between 2018 and 2020. The surface suspended sediment concentration (SSSC) of the Yangtze Estuary was retrieved and verified by the in-situ measured turbidity. Relative SSSC (RSSSC), the ratio of retrieved SSSC to region-averaged SSSC, was then calculated to determine the TMZ (RSSSC>1). The results show that the relation between the SSSC measured in the TMZ core of the SP and river discharge at Datong Gauging Station demonstrated an anticlockwise hysteresis, which can be divided into three stages. In the second stage, the observed SSSCs during the extreme flood were 0.18- 0.68 kg/m3, 0.10- 0.17 kg/m3 higher than before. SSSCs after the extreme flood were lower than those with similar discharge before it in this stage. The TMZ boundary location is correlated logarithmically with river discharge, and the upper boundary moves more seaward than the lower boundary. They moved 6- 20 and - 4- 11 km seaward in the NP and migrated 4- 13 and - 7- 9 km seaward in the SP during the extreme flood, respectively, compared with average annual and usual flood conditions. These findings further clarify TMZ characteristics in extreme floods and can be used as a reference for ecological and waterway projects considering the impacts of extreme flood events.

In many estuaries, current velocity, suspended sediment concentration (SSC), and water depth have notable flood-ebb asymmetries in magnitude or duration. Such asymmetries can make marked impact on estuarine sediment transport and require in-depth analysis of the underlying mechanism. Based on field measurement over a neap-spring cycle in the Changjiang Estuary in January 2015, net suspended sediment transport modulated by multiple asymmetries were analyzed. The results showed that there were notable flood-ebb asymmetries in the current velocity, current duration, SSC, and water depth. The former two were ebb-dominated, while the latter two were flood-dominated. The net suspended sediment transport was landward and exhibited remarkable tidal fluctuation in magnitude. Ebb-dominated velocity and duration asymmetries favored seaward transport, but flood-dominated SSC and water depth asymmetries promoted landward transport. The relative contribution of these asymmetries to the net sediment transport was different and closely related to their asymmetry intensities. The magnitude of net sediment transport was highly modulated by the combined effects of these asymmetries. Further analyses revealed that the ebb-dominated asymmetries in velocity and duration were controlled by river flow, tidal wave deformation, and compensation flow of Stokes drift. The flood-dominated water depth asymmetry was related to the progressive tidal wave. The flood-dominated SSC asymmetry was mainly attributed to the lower SSCs in early ebbs, notable sediment supply limitation in late ebbs, wind wave height asymmetry, and gravitational circulation. Additionally, it is worth noting that the progressive tidal wave can yield strong current asymmetry, notable water depth asymmetry, and obvious wind wave height asymmetry during strong wind periods.

A double-layer transverse oscillating grid for a flume was designed and manufactured, in order to generate approximately isotropic homogeneous turbulence, and allowing the effect of suspended sediment stratification on turbulence characteristics to be studied experimentally. In the experiment, the diachronic variations in turbulence and suspended sediment concentration were measured synchronously using an Acoustic Doppler Velocimeter and a multichannel optical fibre suspended sediment concentration meter. The effect of suspended sediment stratification on turbulence was analyzed in relation to changes in turbulence characteristics, such as root mean square velocity and turbulence intensity. The experimental results confirm that suspended sediment stratification can suppress turbulence and weaken turbulence intensity, and the degree of turbulence suppression is related to the suspended sediment concentration gradient and turbulence intensity. By analogy with the dimensionless Richardson number that characterizes stratification in common ocean models, we define a dimensionless stratification parameter that characterizes the degree of stratification related to turbulence in an oscillating grid. The analysis shows that the turbulence suppression rate is closely related to the stratification parameter in sediment-laden flows. The correlation between turbulence suppression rate and stratification parameter may be obtained using a fitting technique.

Among all marine hazards, storm surges cause the most severe damage, and East Asia is one of the regions in the world most affected by tropical cyclones (TCs). With the increase in global mean temperature, the future changes of tropical cyclone (TC) activities are of great concern in East Asian countries. However, due to the inconsistency among different TC datasets, there is no uniform understanding of the spatial and temporal distribution and trends of TC activities in the eastern sea area of China (ESAC). In this study, all TC wind fields affecting ESAC during 1949-2019 were calculated using the Fujita-Takahashi formula, and a new TC dataset with a spatial resolution of 0.1 degrees x 0.1 degrees was thus obtained. Based on this dataset, the spatial-temporal variations of TC activity were analyzed. Three stages (1949-1967, 1968-1993, 1994-2019) of TC activities in ESAC can be identified using Mann Kendall Trend Test, which is closely related to El Nin similar to o-Southern Oscillation, sunspot activity, and Pacific Decadal Oscillation. A comparison of the accumulative number and duration of TCs in the three stages shows increasing trend toward the coasts and an northward. To address the issue of shelf storm deposition re-cords on ESAC, we compared the published storm depositional records retrieved from several cores with typhoon impact data from the same sites based on the dataset of this study. We found that the preservation potential of the storm deposition record on ESAC ranged from 8% to 33%, with a high preservation potential in shallow water. These findings reveal the distribution and variability of TC impacts, which can be used to provide a scientific basis for disaster prevention and mitigation planning and adjustment of key coastal protection zones, as well as to evaluate the value of marine sedimentary records better.

废黄河三角洲是南黄海内陆架的重要物源.为深入探索废黄河口海域沉积物输运机制,利用2015～2016年夏季与冬季在废黄河口外海域10个站位获取的现场沉积动力数据,计算潮不对称参数、余流、悬沙输运量等.分析结果表明,废黄河口海域沉积物输运模式存在显著的空间差异,大部分海域悬沙沿等深线向南输运,仅在近岸侧局部悬沙向岸或向北输运、离岸最远处站位向北输运但输运率较小;近岸浅水海域以平流输沙为主,其他离岸区域以再悬浮作用为主.由于流速和悬沙浓度之间的相位差,导致余流(净水输运)方向与净悬沙输运方向存在差异.研究沉降速度与悬沙输运涨落潮不对称的关系,发现沉降速度越大,悬沙输运的不对称性就越显著;沉降速度是造成近底部流速与悬沙浓度相位差的主要原因,导致废黄河口外净悬沙输运存在显著的垂向差异.

经典河口环流理论认为河口纵向上存在表层向海、底层向陆的单环流,但该理论中并未包含对地形因素的考虑.本研究于2018年洪、枯季(7、12月)在长江口南槽开展全潮周期的现场调查,通过锚系剖面和座底三脚架观测获得了从陆向海3个站位的同步流速、温盐剖面等数据,探讨了河口拦门沙地形对纵向余环流的影响.研究结果显示,长江口南槽拦门沙海域存在两种河口纵向余环流模式:在洪季形成于拦门沙外坡的经典单环流,而在枯季形成由拦门沙内、外坡环流构成的双环流.基于表征河口混合的Simpson数、M值和盐度剖面结构,揭示拦门沙海域纵向余环流形成的主因是斜压作用;双环流的形成归因于拦门沙地形对枯季盐水入侵的影响,外坡环流亦可能受口外上升流的作用.拦门沙海域双环流结构可显著影响河口滞流点及最大浑浊带悬沙的时空分布,流域和河口人类活动导致的拦门沙地貌形态改变进而又间接影响双环流发生的频率与规模.

开展枯季河口悬沙输运机理研究对于揭示弱径流条件下的陆海相互作用、河口季节性冲淤和水沙关系等具有重要的科学意义.本文根据2018年12月18-25日长江口南槽3个站位连续13个潮周期的同步流速、流向和悬沙浓度等观测资料,运用通量机制分解法研究了各输沙项的特征、贡献和输运机理.结果 表明,从小潮至大潮流速和悬沙浓度不断增加,由南槽上部至下部流速和悬沙浓度逐渐降低.观测期间平均流速与平均悬沙浓度存在明显的正线性关系,但受底质空间差异影响,悬沙浓度对流速的响应强度存在显著的空间变化.枯季期间南槽存在着中上部向陆净输沙、下部向海净输沙的空间输运格局.平流输沙和潮泵输沙是影响和控制净输沙的关键因素,二者的强度和贡献存在明显的潮周期变化和空间变化,垂向环流输沙的强度很弱,对净输沙贡献很小.南槽涨落潮输沙不对称现象明显,流速、悬沙浓度和历时都具有一定的涨落潮不对称性,这些不对称现象共同调节和控制着潮周期净输沙强度和方向的时空变化.

2017年10月在超强台风"兰恩"发生期间,使用三脚架坐底观测系统在长江口南槽进行了 15个潮周期的大潮-小潮的连续观测,获得高精度的盐度、波浪和近底部沉积动力数据.分析表明:台风期间的浪流联合作用控制着南槽的沉积动力过程,实测最大波高为2.1 m,波浪对提高底床切应力有显著贡献;波浪存在明显的涨落潮变化,涨潮阶段有效波高是落潮的1.5～2.7倍,导致涨潮时波浪切应力显著大于落潮;台风对南槽的潮流过程和盐淡水混合程度有明显影响,西北风会抑制涨潮流速并增强水体层化;台风使南槽悬沙浓度显著提高,台风后期近底悬沙浓度高达10 kg/m3,底床上出现厚度超过1.15 m的浮泥层.

Climate change and human activity have exerted significant influences on the sediment load and channel morphology of the Changjiang River system, China. However, our knowledge of their influence on flood regime on the centennial to millennial timescales remains limited, and this is mainly because of the difficulty in directly determining the long-term hydrological variability of the Changjiang River over the period before hydrological gauges were established. Based on multiproxy analysis that combines chronological, sedimentological, and geochemical analysis of a 4.8-m-long sediment core retrieved from the subaqueous delta of the Changjiang River, this study establishes a flood history for the Changjiang River during the late Holocene. Our palaeoflood reconstruction revealed 14 multi-decadal periods of extreme floods (19-66 BCE, 25-80, 255-350, 415-475, 550-710, 740-835, 970-990, 1080-1130, 1170-1235, 1275-1390, 1440-1500, 1560-1730, 1810-1830, and 1950-2011 CE). These flood units match well with the observed large floods, documentary records of floods, and sedimentary flood deposits, confirming that the coarse units in the sequence are flood-derived and are regionally representative. Comparing with regional and global palaeoclimate records indicates that major flood events of the Changjiang are strongly modulated by the Asian summer monsoon and the El Nino-Southern Oscillation (ENSO), but that anthropogenic impacts (e.g. artificial channelization and land clearance) have also greatly amplified the flooding frequency over the past 600 yr.

Reclamation in estuaries can greatly change the channel geometry and hydrodynamic conditions and these changes may have significant impacts on spatial and temporal distribution of the turbidity maximum zone. This study focuses on the effects of a large area of reclamation built in 2007-2018 and the behavior of the turbidity maximum zone along the North Channel of the Yangtze Estuary. Data were collected of bathymetry in the North Channel, tidal elevations at Sheshan Station, river discharge at Datong Station and turbidity, retrieved from six Landsat remote sensing images in the dry season from 2006 to 2019. In-situ measured data on flow velocity and suspended sediment concentration were obtained in the dry season of 2003 and 2018. Analysis of the data revealed that reclamations, which led to narrowing (0.86-2.74 km) and fixing of the channel, caused erosion of 0.19-3.72 m in the deep channel and deposition on the tidal flats. Furthermore, it was found that the length of the turbidity maximum zone decreased: its landward boundary shifted 5 km seaward during spring tide and 17 km seaward during neap tide in the dry season. The position of the seaward boundary wandered within a range of 3 km, being further downstream during neap tide than that during spring tide. A conceptual model of changes in the borders of the turbidity maximum zone in response to reclamation is proposed. After the reclamation works, the deeper and narrower channel intensified ebb-dominance of the flow velocity. The coarsening of bed sediment weakened resuspension and decreased the bottom tidally averaged suspended sediment concentration. These changes led to a significant decline in the depth-mean of tidally averaged suspended sediment concentration and caused the seaward movement of the landward boundary of the turbidity maximum zone.

Classical estuary circulation theory states that in the longitudinal direction of an estuary there exists a single circulation with landward, near-bottom, and seaward, near-surface flows; however, the situation becomes complicated with the presence of a river mouth bar. Here we conducted tidal-cycle observations in the South Passage of the Yangtze Estuary during both the wet and dry seasons of 2018 (July and December, respectively). The simultaneous current velocity, temperature, and salinity profile data were obtained from anchored boats and base tripods at three stations along the channel in the mouth bar area. The results reveal two distinct longitudinal residual circulation patterns: a classic circulation which is formed on the seaward slope of the mouth bar during the wet season, and a double circulation system which is composed of two circulation cells over the landward and seaward slopes of the mouth bar during the dry season. The Simpson number (Si), mixing parameter (M), and salinity data were used to quantify the mixing intensity, which shows that horizontal baroclinic pressure gradient is the dominant factor in the formation of the longitudinal residual circulation. Furthermore, the double circulation pattern during the dry season is related to the mouth bar bathymetry, which affects saltwater intrusion. The double circulations can significantly influence the spatial and temporal evolution of the stagnation point in the estuarine channel, which in turn modifies the distribution patterns of suspended sediment concentration in the maximum turbidity zone. Evidently, the changes in the mouth bar sandbar bathymetry in response to human activities and river basin hydrographic conditions indirectly affect the occurrence and scale of the double circulations.

Driven by global changes and human activities, the sediment source/transport, and riverbed erosion and deposition pattern of the Yangtze River Basin are undergoing continuous adjustments, which influence both magnitude and property of fluvial sediment to the estuary. In order to explore sediment transport and correlated topographic changes of the Yangtze River Estuary within 40 years in response to variations of fluvial sediment discharge from the upstream basin, this study uses sediment grain size trend models and multi-year zonal analysis methods to predict temporal and spatial variations of morphological changes within the Yangtze Estuary, based on grain size data and topographic data from 1980 to 2020. The results show that sediments converge toward the center of the channel within the northern branch, and a deposition center forms close to the south and north channel diversion area within the southern branch, consistent with the morphological changes between 2012 to 2020 calculated from sea maps, validating the effectiveness of the grain size trend model in predicting morphological changes within the Yangtze River Estuary. The results of the multi-year zonal analysis show that: 1980—2003 was characterized by a high volume of fluvial sediment discharge, and the entire estuary area was dominated by deposition with slightly finer sediment. Fluvial sediment discharge experienced a rapid decrease from 2003 to 2012, while the estuary area was still dominated by deposition before 2009 with similar grain size. 2009—2012, however, was a transitional period when erosion and sediment coarsening started to appear out of the estuary, although limited to small areas. From 2012 to 2020, large-scale erosion and grain size coarsening occurred widely in the estuary, and a significant correlation was found between the particle size and the magnitude of erosion. Our study shows that high-resolution zonal analysis can effectively catch the local morphological change signals in the Yangtze River Estuary. In the past 40 years, the Yangtze River Estuary has changed from deposition-dominant mode to partially erosion mode, and it may face continuous coastal erosion in the future.

The vertical density gradients of salinity and suspended sediment concentration (SSC) cause stratification in estuaries, which play a vital role in the turbulence structure, water mixing, and sediment transport. To investigate the effect of stratification, especially SSC-induced stratification, on maintaining the estuarine turbidity maximum (ETM), we conducted in situ measurements on sediment dynamics at the upper and central ETM sites in the South Passage of Changjiang Estuary in July 2018. The gradient Richardson number was estimated as a proxy for the stratification that is attributable to salinity or/and SSC. We found that salinity-induced stratification was observed mainly on the surface and in the middle layers, whereas SSC-induced stratification occurred mainly in the near-bottom layers. Furthermore, at the central ETM, the baroclinic effect was enhanced during the neap tide when the salinity-induced stratification was stronger than that during the spring tide. In the early phase of floods with minimum velocity during the neap tide, salinity-induced stratification suppressed the turbulence and vertical diffusion of sediments. Moreover, the flocculation enhanced the settling process within the water column. Consequently, high concentrations of fine-grained sediments formed near the bottom and promoted SSC-induced stratification, thereby leading to the continuous accumulation and trapping of sediments. In conclusion, the interactions among the “salinity- and SSC-induced stratification” processes served as crucial constraints of the temporal and spatial variations of the ETM in the Changjiang Estuary.

This study investigated the polycyclic aromatic hydrocarbons (PAHs) occurrence, and their impact on the microbial community and PAH-degrading genera and genes in the Knysna Estuary of South Africa. The results reveal that the estuary exhibits low PAH levels (114.1-356.0 ng g(-1)). Ignavibacteriae and Deferribacteres, as well as Proteobacteria and Bacteroidetes, are keystone phyla. Among measured environmental factors, total organic carbon (TOC), nutrients such as nitrite and nitrate, metals as Al, Cr, Cu, Ni, Pb and Zn, and environmental properties (pH and salinity) are primary contributors to structuring the bacterial community assemblage. The abundance of alpha subunit genes of the PAH-ring hydroxylating dioxygenases (PAH-RHD alpha) of Gram-negative bacteria lies in the range of (2.0-4.2) x 10(5) copies g(-1), while that of Gram-positive bacteria ranges from 3.0 x 10(5) to 1.3 x 10(7) copies g(-1). The PAH-degrading bacteria account for up to 0.1% of the bacterial community and respond mainly to nitrate, TOC and salinity, while PAHs at low concentration are not significant influencing factors. PAH degraders such as Xanthomonadales, Pseudomonas, and Mycobacterium, which play a central role in PAH-metabolization coupled with other biogeochemical processes (e.g. iron cycling), may contribute to maintaining a healthy estuarine ecosystem. These results are important for developing appropriate utilization and protection strategies for pristine estuaries worldwide. (c) 2020 Elsevier Ltd. All rights reserved.

Coastal deltaic deposits are the primary locations for sediment storage on Earth, and quantifying their source contributions is a critical prerequisite for delineating S2S patterns in marginal seas. In most cases, quantification for the contribution by fine‐grained sediments (i.e. particle size < 63 μm) is considered to be representative to constrain the overall sediment supply. However, this approach may be inappropriate because large differences exist between the two quantities. Here we propose an approach to solve the problem, which is based on the maximum number of tracers from multiple sediment size fractions incorporating the content of all size fractions of sediment. Using this approach, absolute source contributions during the Holocene are reconstructed that provide a first‐order model for the S2S pattern of the central Jiangsu coast, China. The Huanghe River is the strongest driver for the Holocene sedimentation, with a mean contribution of ~72 ± 6% (1417 × 108 t). The absolute contributions from the Changjiang and offshore areas were of secondary importance, (i.e. ~17 ± 1% (330 × 108 t) and ~11 ± 5% (217 × 108 t), respectively). The results show that a large difference between the relative and absolute source contributions and the assumption that the relative contribution represents the absolute contribution is invalid in a coastal setting. The impact of the Huanghe is mainly based on episodic events, such as the event of 1128–1855 AD. The model also reveals that the offshore sediments are as important as the Changjiang sediments for the central Jiangsu coast during the Holocene. Thus, the model provides both the time series and overall quantities of sediment supply during the formation and evolution of the Holocene tidal flats on the Jiangsu coast. Our findings shed new light on quantitative analysis of sediment sources applicable to future S2S studies of marginal seas. © 2020 John Wiley & Sons, Ltd.

Due to the impact of the Three Gorges Dam on water and sediment storage, the sediment flux into the Yangtze River Estuary has dropped sharply by 70%, and the suspended sediment concentration in the estuary has responded accordingly. From the comparison of the measured suspended sediment concentration data of the Yangtze River estuary for many years, it is known that the suspended sediment concentration in the South Passage has been reduced by about 60% recently, and that in the middle and upper reaches of the North Channel and the South Channel has been reduced by about 40%. On the other hand, A series of artificial engineering has been completed in the past 20 years, such as the 12.5m Deep-Waterway Regulation Engineering, the Nanhui Shoal Slush-enclosure Engineering, and the Hengsha Shoal Slush-enclosure Engineering, etc. These engineering have significantly changed the original water and sediment transport pattern of the Yangtze River Estuary. It resulted in a significant change of the estuarine turbidity maximum zone and the corresponding river mouth bar topography. This paper intends to discuss the impact of human activities on the dynamic sedimentation process of the maximum turbidity zone in the Yangtze River Estuary based on field measured data. Results are as follows: (1) Compared to two decades ago, the suspended sediment concentration in the North Passage, the South Passage and the North Channel, and the middle and lower reaches of the North Branch is still high, which is related to the existence of the turbidity maximum zone and river mouth bar in these river sections. (2) The implementation of man-made engineering such as the submerged diversion dike between the North Passage and the South Passage and the Nanhui Shoal Slush-enclosure Engineering changed the flow structure in the upper section of the South Passage, leading to the turbidity maximum zone and the corresponding river mouth bar have completely disappeared. (3) Affected by the 12.5m Deep-Waterway Regulation Engineering, the turbidity maximum zone and the corresponding river mouth bar originally located at the upper section of the North Passage have also disappeared. (4) The longitudinal circulation flow structure, salt water wedges, and stagnation points in the middle and lower sections of the North Passage and the South Passage still exist. The positions of the turbidity maximum zone and the corresponding river mouth bar topography are not significantly affected by the engineering. And the core area of ​​the obvious turbidity maximum zone and the river mouth bar (only in the South Passage) still exist. Due to the artificial dredging of the navigation channel in the North Passage, it actually appeared as an invisible river mouth bar that has been dredged by continuous dredging. (5) The drastic reduction of sediment flux from the basin has caused seabed erosion adjacent to the Yangtze River Estuary, and the corresponding eroded sediment has become one of the main sediment budget sources of the turbidity maximum zone.

为了探讨长江口潮差的中长期变化对生态环境的影响,利用小波变换法对1972—2018年该河口代表性潮位站的潮差序列(共66336个数据)进行周期性分析.结果表明,该站潮差除了常见的15 d大、小潮周期外,还有变幅约19 cm(相当于多年平均潮差的7.5％)的0.5 a周期和变幅约16 cm(相当于多年平均潮差的6.3％)的18.5 a周期.月均潮差极大值出现在3月和9月,极小值出现在6月和12月.年均潮差极大值出现在1977,1996和2015年,极小值出现在1986年和2005年.上述潮差变化在时间上与长江口灾害性盐水入侵、悬沙浓度长周期变化以及水下三角洲冲淤转变等重大事件存在明显的对应关系.结论认为,上述中长期潮差周期变化对长江口生态环境具有不可忽视的潜在影响,在今后对河口生态环境的研究中应得到重视.

The link between tropical cyclone (TC) activity in the South China Sea (SCS) and global climate change is commonly debated and there is a clear need for long-term geological records of TC activity if we are to clarify this connection. Multi-millennial, high-resolution paleo-storm records from the SCS are rare in the region and this causes difficulties for those exploring potential climate drivers of TC variability over centennial to millennial timescales and reduces our ability to fully assess the risks associated with future TC activity. This paper presents an age-constrained, mud-dominated sedimentary sequence from a coastal lagoon on Hainan Island, China. Multiproxy analyses incorporating chronological, lithological, sedimentological, and geochemical evidence were used to infer storm deposits preserved within the sequence and to reconstruct a time series of storm activity in the SCS during the mid-to-late Holocene. This long sedimentary record shows that TCs were highly active over the periods 5500 to 3500 and 1700 to 0 cal yrs. BP, and these periods contrast with a relatively quiet period 3500-1700 cal yrs. BP. An apparent inverse correlation between TC reconstructions from the SCS and those from the Korean Peninsula and Japan implies an oscillating pattern across the SCS and western North Pacific (WNP) over centennial to millennial timescales. A comparison between the sedimentary and paleoclimatic records implies that the El Nino-Southern Oscillation was not the only mechanism responsible for typhoon variability over the past 7500 cal yrs. BP, suggesting that other factors such as the thermal state of the western Pacific warm pool likely also had a strong influence on both SCS and WNP TC variability.

在全球气候变化和人类活动影响加剧的背景下,作为河口海岸重要子系统的三角洲正在发生快速变化.长江三角洲地处长江入东海交汇处,是中国最重要的经济核心区之一,对邻近区域乃至整个长江经济带经济社会发展都起着重要作用.由于全球变暖、海面上升和强烈人类活动引发了三角洲系统状态转换,因此以往基于恒定系统状态而获得的有关长江三角洲的认识已不能满足未来需求,迫切需要对未来海面变化、极端事件、流域与河口工程影响下的三角洲物质循环条件、物理过程、地貌冲淤演化、源-汇格局调整等科学问题进行深入研究.在三角洲系统行为、未来演化趋势的预测能力建设中,应重视从海面到海底的综合立体观测系统的发展,以获取关键数据;基于三角洲系统的时、空演化特征,建立三角洲本征态和衍生态的谱系理论.未来需针对系统状态转换而调整原先的经济社会发展模式,以便保护自然资源、重建生态系统,更好地支撑长江经济带发展,重绘长江三角洲发展蓝图.