南海周边相对海平面变化特征及2004年苏门答腊地震影响分析

利用南海周边1989-2014年的潮汐资料和GPS长期观测资料,分析了南海周边相对海平面变化特征,以及2004年苏门答腊地震对该区域相对海平面变化的影响。研究结果表明,南海周边的相对海平面变化以上升为主,平均上升速率（4.53±0.20） mm/a,高于全球平均速率,且2004年后上升趋势加剧;南海周边相对海平面呈现6类较典型的变化特征,并存在与板块构造相对应的分区聚集现象,形成了中国东南和越南沿海、马来半岛、加里曼丹岛北部、菲律宾群岛等4个变化特征区。受2004年苏门答腊大地震的影响,马来半岛、南沙和西沙海域的地壳形变由上升趋势转为下沉,加剧了相对海平面的上升;中国东南沿海和菲律宾群岛受地震影响较小;越南沿海和加里曼丹岛北部区域的地震影响还有待进一步研究。     

福建沿岸6000年来的海平面波动

本文通过35个~(14)C测年数据进行评价,建立一条福建省沿岸过去6000年海平面变化曲线,该线表明海平面在现代位置上下呈振荡性变化,最高和最低海平面分别出现距今5000年前和4000年前左右,海平面高度分别为约+2m,-2m。     

华南弧形砂质海岸形成机制分析

对华南弧形砂质海岸体系的沉积环境、动力及其泥沙供给等条件进行了分析．结果表明：控制华南弧形砂质海岸形成的主要因素包括地域背景、陆架物质供应量、水动力条件、海平面变化等．其中，陆架供沙是弧形砂质海岸形成的主导因子，海面上升致使大量泥沙存在向岸运动的趋势；波浪则是叠加在这种趋势上促使泥沙向岸运动的动力因子．     

Numerical Study of the Upper-Layer Circulation in the South China Sea

Upper-layer circulation in the South China Sea has been investigated using a three-dimensional primitive equation eddy-resolving model. The model domain covers the region from 99° to 122°E and from 3° to 23°N. The model is forced by the monthly averaged European Centre for Medium-Range Weather Forecasts (ECMWF) model winds and the climatological monthly sea surface temperature data from National Oceanographic Data Center (NODC). Inflow and outflow through the Taiwan Strait and the Sunda shelf are prescribed monthly from the Wyrtki estimates. Inflow of the Kuroshio branch current in the Luzon Strait is assumed to have a constant volume transport of 12 Sv (1 Sv = 10⁶ m³/s), and the outflow from the open boundary to the east of Taiwan is adjusted to ensure the net volume transport through all open boundaries is zero at any instant. The model reveals that a cyclonic circulation exists all year round in the northern South China Sea. During the winter time this cyclonic eddy is located off the northwest of Luzon, coinciding with the region of positive wind stress curl in this season. This cyclonic eddy moves northward in spring due to the weakening of the northeast winds. The cyclonic circulation becomes weak and stays in the continental slope region in the northern South China Sea in the summer period. The southwest wind can raise the water level along the west coast of Luzon, but there is no anticyclonic circulation in the northern South China Sea. After the onset of the northeast monsoon winds in fall, the cyclonic eddy moves back to the region off the west coast of Luzon. In the southern South China Sea and off the Vietnam coast, the model predicts a similar flow structure as in the previous related studies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Human impacts overwhelm the effects of sea-level rise on Basque coastal habitats (N Spain) between 1954 and 2004

According to coastal measurements, global mean sea-level has risen at a rate of 1.8 mm yr⁻¹ between 1950 and 2000, with large spatial variability at regional scales. Within the Bay of Biscay, trends computed from coastal tide gauges records have revealed that sea-level rise is accelerating over this period of time; this is in agreement with rates obtained from satellite imagery in the open ocean since 1993. The objectives of the present study are: (1) to assess the evidence of the relative sea-level rise on coastal morphology and habitats in the Gipuzkoan littoral zone (Basque coast, northern Spain) for the period 1954–2004, and (2) to evaluate the relative contribution of local anthropogenic versus sea-level rise impacts for explaining inter-supratidal habitat changes. A high-resolution airborne laser altimetry data (LIDAR) has been used to derive a Digital Terrain Model (DTM) of 15-cm vertical resolution. Coastal habitats were mapped for two periods, using historic airborne photography (1954) and high-resolution imagery (2004). Analysis of tide gauge records from Santander (northern Spain) has revealed that relative mean sea-level has been rising at a rate of 2.08 ± 0.33 mm yr⁻¹ from 1943 to 2004; this is consistent with sea-level trends from other measurements within the area (St. Jean de Luz and Bilbao), obtained over shorter periods of time, and with previous results obtained in the Bay of Biscay. Based upon this sea-level trend and by means of a LIDAR-based DTM, the results have indicated that the predicted change along the Gipuzkoan coast due to sea-level rise was of 11.1 ha within the 50-yr period. In contrast, comparison of historical and recent orthophotography has detected only 2.95 ha of change, originated possibly from sea-level rise, and 98 ha transformed by anthropogenic impacts. Hence, coastal changes due to sea-level rise might be overwhelmed by excessive human impacts, at the spatial and temporal scales of the analysis. This work highlights that local anthropogenic impact is the major threat to Basque coastal and estuarine habitats, compared with natural erosive processes and global climate change driving forces over recent times.     

Morphodynamics of a high discharge tropical delta, San Juan River, Pacific coast of Colombia

The San Juan River has one of the most extensive and best developed deltas on the Pacific coast of South America, measuring 800 km². The river drainage basin measures 16?465 km² and is located in one of the areas with the highest precipitation in the western hemisphere. The annual rainfall varies from 7000 to 11?000 mm, and as a result the San Juan River has the highest water discharge (2550 m³ s⁻¹), sediment load (16×10⁶ t yr⁻¹), and basin-wide sediment yield (1150 t km⁻² yr⁻¹) on the west coast of South America. The San Juan delta growth began approximately 5000 years BP. The structure of the delta is determined by the interactions between fluvial deposition and the effect of 1.7-m significant swells, mostly from the SW, and strong tidal currents. Analysis of delta progradation indicates that during 1848-1992 the morphology of the delta was characterized by beach ridge accretion, spit growth, narrowing of inlets, and a general advance of the delta shoreline. During the past decade processes such as rapid erosion of the delta shore, narrowing of barrier islands, and breaching of a new inlet, are the result of a long-term relative sea-level rise of 2.6 mm yr⁻¹ due to tectonically induced subsidence coupled with a eustatic rise of sea-level. The delta also experiences strong oceanographic manifestations associated with the El Niño-La Niña cycle, causing regional sea-level elevation of 20-30 cm during El Niño years. Recent coastal subsidence in the delta is evidenced by: (1) increased occurrence of non-storm washover events; (2) increased erosion of barrier islands with average loss of 11 m yr⁻¹ during 1993-1997; and (3) a relative sea-level rise of 3.4 mm yr⁻¹ during 1991-1999. The morphology and recent evolution of the San Juan delta are unique when compared to other deltas of South America because of the singular combination of extreme climatic, geologic, and oceanographic conditions under which the delta has formed and the absence of human-induced impact in the drainage basin.     

华南砂质海滩的动力地貌分析

为探讨华南砂质海滩的动力地貌学特征,对不同地理岸段不同地貌形态的8 个沙滩剖面于冬、夏季进行现场重复调查和室内分析工作.据此,通过对华南海岸带地质构造、地貌和现代海岸动力环境地域变化的分析,将华南沿海砂质海岸划分为岬湾岸、沙坝-潟湖岸和夷直岸三种基本海岸地貌类型,并且从滩面倾向、海岸动力环境影响、季节冲淤变化趋势和滩面沉积物粒径、坡度的动力响应等方面探讨砂质海滩的动力地貌,得出其受制于多种环境因素的影响,其中地质构造背景和海平面变化为大尺度的砂质海岸地貌的发育奠定了基础,而全新世海侵海平面相对稳定后,海岸动力条件的塑造起着决定性的影响,浪潮作用指数是其中重要的影响指标.     

Paleoenvironmental implications of the guano phosphatic cementation on Dongdao Island in the South China Sea

The phosphatic cement in the bioclastic sediment sequence on the northeastern shore of Dongdao Island in the South China Sea was studied and its paleoenvironmental implications discussed. Petrological characteristics and major, trace, REE element data unequivocally supported the notion that phosphatization was closely associated with avian guano decomposition and leaching, whereas carbon and oxygen isotope results further revealed that meteoric water were involved in these processes. AMS ¹⁴C dates on the brown phosphate cements indicate that they were formed around 5700, 5000–5100 and 2900 yr BP, respectively. The multi-episodes of phosphatization very likely correspond to intermittent seabird occupation on this island — possibly reflecting Holocene sea-level oscillation and/or long term climate changes in the South China Sea that have controlled seabird habitat. The phosphate cementation, which occurs widely in tropical islands, may be another useful monitor for sea-level and/or paleoclimate changes.     

Plio–Quaternary sedimentation processes and neotectonics of the northern continental margin of the South China Sea

Analyses of over 6600 km of reflection seismic profiles on the northern continental margin of the South China Sea permit the recognition of four Quaternary high-frequency type 1 sequences of the 4th order, deposited during the past ca. 690 kyr. At the present-day shelf edge, only lowstand systems tracts characterised by a prograding clinoformal internal reflection pattern are preserved. The prograding complexes can be considered as regressive units accumulated during relative sea-level falls. They exhibit internal discontinuities which might point to minor sea-level fluctuations of the 5th order. A preliminary regional relative sea-level curve for the past 630 kyr is established using the present positions of the delta fronts mapped. The neotectonics curve derived by subtracting eustatic sea-level changes from the relative sea-level curve shows that the depths of the delta fronts today are controlled primarily by regional tectonic movements and the global sea-level.Our seismo-stratigraphic interpretation documents that the area off Hong Kong and around the Dongsha Islands experienced two uplift episodes during the past 5 ma, namely at the Miocene/Pliocene boundary and at the end of the lower Middle Pleistocene, respectively. These uplift events which are centred on the Dongsha Rise led to its subaerial exposure and to the erosion of the Pliocene and most of the Pleistocene strata. The change from thermal subsidence of the continental margin initiated at the end of the drift phase to the phase of magmato-tectonic uplift was caused by a reorientation of the tectonic regime.The Recent depositional environment on the northern continental margin of the South China Sea is dominated by sediment accumulation within the inner shelf and the Zhujiang (Pearl River) estuary. The outer shelf and upper slope, especially around the Dongsha Islands, are characterised by bypass of terrigenous material.The sedimentary column in the deepsea basin has a thickness of more than 2 km and comprises 14 depositional units starting with terrestrial rift deposits. It overlies oceanic as well as transitional crust.     

Length variation of the oceanic coasts as a cause of eustatic sea-level changes

The volume of the continental and continent-derived matter in oceanic basins can be inferred from their bathygraphic curve: coeteris paribus, this volume depends upon the length of the corresponding coasts. Although the present-day order of magnitude of its equivalent sea-level rise per kilometre of coast is no more than some millimetres, large-scale variations of the length of oceanic coasts — like those which may have taken place following upon continental drifting — may have been a cause of important eustatic sea-level changes both positive and negative.     

Seismic expression and inferred depositional environments of Plio-Pleistocene sedimentary sequences in the southwestern Caspian Sea

Eight seismic profiles from the southwestern Caspian Sea were analyzed to establish the sedimentary environments and depositional history in the South Caspian Basin since Pliocene times. Based on reflection terminations, nine sequence boundaries (S1 to S9) were identified and traced across the study area. Consequently, nine depositional sequences (S1–S9) were defined on the basis of seismic facies analysis. The results suggest a transition from non-marine sedimentation in the Lower Pliocene to marine-dominated conditions in the Upper Pliocene (S1–S4). Marine conditions then continued to the present time; however, several sea-level changes led to the formation of sequences S5 to S9. Although no local sea-level curve is available due to a lack of well data, there is good agreement between the seismic stratigraphy of the study area and a published regional sea-level curve.     

粤西博贺沙坝-澙湖海岸及其近岸海床稳定状态分析

结合华南弧形海岸的平衡与稳定特征，利用Gis和Envi软件对不同年份的海图进行数字化、等深线变化和海床冲淤计算对比．结果表明博贺沙坝-澙湖海岸近岸线处为相对淤积的动态平衡状态，近岸带海床相对稳定、海床冲淤幅度不大．但由于当前海面趋于上升、陆架泥沙来源减少以及近岸波浪等动力作用可能加强，近岸海床将出现由淤转冲的趋势．     

粤西博贺沙坝-潟湖海岸及其近岸海床稳定状态分析

结合华南弧形海岸的平衡与稳定特征,利用Gis和Envi软件对不同年份的海图进行数字化、等深线变化和海床冲淤计算对比.结果表明博贺沙坝-潟湖海岸近岸线处为相对淤积的动态平衡状态,近岸带海床相对稳定、海床冲淤幅度不大.但由于当前海面趋于上升、陆架泥沙来源减少以及近岸波浪等动力作用可能加强,近岸海床将出现由淤转冲的趋势.     

中国沿岸现代相对海平面上升加剧

本文用线性回归方法,分两个时段分析了中国沿岸２５个验潮站相对海平面的年变化速度,计算了相应时段的平均海面,结果表明,中国沿岸现代相对海平面上升加剧。另外,本文还对海平面变化原因进行了讨论。     

Latitudinal gradients and poleward expansion of mangrove ecosystems in South Africa: 50 years after Macnae’s first assessment

Mangroves occur in South African estuaries at their poleward distribution limits, extending into temperate habitats. In 1963, William Macnae published the first comprehensive assessment of mangrove swamps in South Africa and made firsthand observations of these mangrove ecosystems. This article reassesses South African mangrove habitats, highlighting changes since Macnae’s assessment, through a literature review of research done in the past 50 years and using the results of a dedicated mangrove survey spanning 2012–2017. Until now, changes have been recorded mostly for mangrove vegetation, including a change in mangrove cover and a poleward shift of mangrove species. While some mangrove-associated fauna have disappeared from most sites (e.g. the gastropod Terebralia palustris), others, such as fiddler crabs, have spread farther south. The effects of decreasing diversity with an increase in latitude were not observed along the South African coast. Instead, habitat quality and estuarine mouth state seem to exert greater influence on species diversity in the mangroves, and a poleward shift in species distribution is now evident not just for the mangrove flora but for the fauna as well. South African mangrove research needs to include a continuous monitoring plan, especially if we are to contribute to global knowledge on blue carbon, the effects of sea-level rise, and the resilience of the mangrove ecosystem.     

Impact of dynamic feedbacks between sedimentation,sea-level rise,and biomass production on near-surface marsh stratigraphy and carbon accumulation

Salt marshes accrete both organic and inorganic sediments. Here we present analytical and numerical models of salt marsh sedimentation that, in addition to capturing inorganic processes, explicitly account for above- and belowground organic processes including root growth and decay of organic carbon. The analytical model is used to examine the bias introduced by organic processes into proxy records of sedimentation, namely ¹³⁷Cs and ²¹⁰Pb. We find that accretion rates estimated using ²¹⁰Pb will be less than accretion rates estimated using the ¹³⁷Cs peak in steadily accreting marshes if (1) carbon decay is significant and (2) data for ²¹⁰Pb extend below the ¹³⁷Cs peak. The numerical model expands upon the analytical model by including belowground processes such as compaction and root growth, and by explicitly tracking the evolution of aboveground biomass and its effect on sedimentation rates. Using the numerical model we explore how marsh stratigraphy responds to sediment supply and the rate of sea-level rise. It is calibrated and tested using an extensive data set of both marsh stratigraphy and measurements of vegetation dynamics in a Spartina alterniflora marsh in South Carolina, USA. We find that carbon accumulation in marshes is nonlinearly related to both the supply of inorganic sediment and the rate of sea-level rise; carbon accumulation increases with sea-level rise until sea-level rise reaches a critical rate that drowns the marsh vegetation and halts carbon accumulation. The model predicts that changes in carbon storage resulting from changing sediment supply or sea-level rise are strongly dependent on the background sediment supply: if inorganic sediment supply is reduced in an already sediment poor marsh the storage of organic carbon will increase to a far greater extent than in a sediment-rich marsh, provided that the rate of sea-level rise does not exceed a threshold. These results imply that altering sediment supply to estuaries (e.g., by damming upstream rivers or altering littoral sediment transport) could lead to significant changes in the carbon budgets of coastal salt marshes.     

High-resolution records of the response of coastal wetland systems to long-term and short-term sea-level variability

While it is well known that coastal systems respond to long-term sea-level changes, the importance of short-term sea-level dynamics is often overlooked. Year-to-year variability in annual mean sea level along the North American Atlantic coast is part of a regionally consistent pattern that is coupled to low atmospheric pressure and high wind field anomalies persisting over 100s to 1000s of km. These short-term sea-level dynamics, along with long-term sea-level changes are shown to be closely coupled to a set of high resolution excess ²¹⁰Pb geochronologies from four physiographically distinct salt marsh estuaries surrounding Long Island, NY, USA. However, the degree to which a marsh responds to either forcing depends on its physiographic setting. Accretion and mineral deposition rates in marshes situated in embayments with long fetches and low-tidal ranges are shown to respond most to the short-term dynamically driven changes in sea level. On the other hand, accretion and mineral deposition in a marsh in an embayment with a high-tidal range and reduced fetch best track the long-term changes in mean sea level, presumably because the physiography limited the meteorological drivers of short-term sea-level change. The close coupling between marsh accretion, physiographic setting and indices of sea-level change indicates that these coastal system respond both differently and rapidly (2–5 yr) to climate variability.     

Io/U ages of corals from Saurashtra coast

Un-recrystallized fossil corals occurring at 2–6 m above the present mean low-tide level on the Saurashtra coast (Western India) have been dated by ²³⁰Th/²³⁴U and ²³⁴U/²³⁶U radiometric methods. The measured ages of the corals, which are in agreement with radiocarbon ages, fall in three groups, 6,000, 30,000 and 120,000 years before present. This observation, coinciding with the high sea-level stands reported in several locations in the world, in the absence of evidence in support of instability of Saurashtra coast, suggests that the coral reefs are remnants of one Holocene and two Quaternary high sea-level stands.     

南海周边中全新世以来的海平面变化研究进展

综述了近几十年来前人有关中全新世以来南海海平面变化研究的主要成果,着重探讨了研究中出现的争议和热点问题,结果表明,南海中全新世确实存在高海平面,海平面最高有2~3 m,出现在7.0~5.5 kaBP;而此后的海平面变化呈振荡模式,波动降低到目前海平面的位置,且与温度波动有一定的同步性,揭示了它们之间的紧密联系。而由卫星观测结果统计出的最近十几年以来南海海平面的上升速率达3.9 mm/a,略高于同期全球平均值;由验潮站统计出的南海海平面上升率为2.4 mm/a,同样略高于相应的全球平均值。最后还指出了研究过程中存在的主要问题与不足,并初步总结出一些改进措施:①使用高精度的定年技术,减少年龄误差;②在构造相对稳定的海岸段研究古海平面变化;③尽量采用高精度的标志物,如微环礁、管形虫壳等。     

CONTINENTAL SHELF WAVES ALONG THE COASTS OF CHINA

Spectral analyses have been carried out on the time-series data from 16 tide stations and nearby weather stations along the coasts of China during the winter of 1980-1981 and the summer of 1981. After removing the wind and barometric effects, the authors found the signals of the southward moving sea-level variations at about 0.21 and 0.32 cpd along the coasts of the Huanghai Sea, East China Sea and South China Sea in winter, and only the 0.26 cpd southward moving sea-level variations along the coast of the South China Sea in summer. Using simple analytical models based on idealized bottom profiles of the China Seas, the observed phenomena can be explained as the lowest-mooe continental shelf waves travelling along the coasts of China.