Relative sea level fluctuations in aegean coastal areas from middle to late holocene

The current study presents and combines data concerning relative sea level fluctuations from six coastal areas in the Aegean Sea, from Thrace to North-Eastern Crete. These data have been derived from analyses and geo-chronologies on coastal sediments obtained from boreholes in coastal lagoons and from beachrock bends. Trends of relative sea level change at the study areas are presented for the last 6000 years and are compared with K. Lambeck's and A. Purcell [1] estimations for the same areas. It is concluded that sea level is rising faster in Skyros and Mykonos-Delos insular complex of Cyclades islands, mainly due to tectonic movements or lithosphere elastic deformations.     

Formation and preservation of an overstepped segmented lagoon complex on a high‐energy continental shelf

The duration of shoreline occupation at a given sea‐level, coastal response to sea‐level change and the controls on preservation of various shoreline elements can be recognized by detailed examination of submerged shorelines on the continental shelf. Using bathymetric and seismic observations, this article documents the evolution and preservation of an incised valley and lithified barrier complex between ?65 m and ?50 m mean sea‐level on a wave‐dominated continental shelf. The barrier complex is preserved as a series of aeolianite or beachrock ridges backed by laterally extensive back‐barrier sediments. The ridges include prograded cuspate lagoonal shoreline features similar to those found in contemporary lagoons. The incised valley trends shore‐parallel behind the barrier complex and records an early phase of valley filling, followed by a phase of extensive lagoonal sedimentation beyond the margins of the incised bedrock valley. Sea‐level stability at the outer barrier position (ca ?65 m) enabled accumulation of a substantial coastal barrier that remained intact during a phase of subsequent slow sea‐level rise to ?58 m when the lagoon formed. These lagoonal sediments are stripped seawards by bay ravinement processes which caused the formation of several prograded marginal cuspate features. An abrupt rise in sea‐level to ?40 m, correlated with melt‐water pulse 1B, enabled the preservation of thick lagoonal sediments at the top of the incised valley fill and preservation on the sea bed of the cemented core of the barriers. This situation is unique to subtropical coastlines where early diagenesis is possible. The overlying sandy sediment from the uncemented upper portion of the barriers is dispersed by ravinement, partly burying the ridges and protecting the underlying sediments. The high degree of barrier or shoreline preservation is attributed to rapid overstepping of the shoreline, early cementation in favourable climatic conditions and the protection of the barrier cores by sand sheet draping.     

Holocene cemented beach deposits in Belize

Two types of cemented beach deposits occur on reef islands off the coast of Belize. These are (1) intertidal beachrock that is dominantly cemented by marine aragonite and high-magnesium-calcite cements, and (2) supratidal cayrock that is cemented mainly by vadose low-magnesium-calcite cements. Besides differences in position relative to present sea level and resulting early diagenesic features, beachrock and cayrock can be distinguished on the basis of differences in composition, texture, geographical position, and age. Whereas the composition of beachrock is similar to that of the adjacent marginal reef sediments, cayrock is enriched in benthic foraminifera. Intertidal beachrock is moderately to well sorted and well cemented, while supratidal cayrock is very well sorted, poorly cemented and friable. Beachrock occurs preferentially on windward beaches of sand-shingle Gays on the middle and southern barrier reefs and on the isolated platforms Glovers and Lighthouse Reefs. Cayrock only occurs on larger mangrove-sand Gays of the isolated platforms Turneffe Islands, Lighthouse Reef, and the northern barrier reef. ¹⁴C-dating of ten whole-rock and mollusk shell samples produced calibrated dates between AD 345 and AD 1435 for beachrock and between BC 1085 and AD 1190 for cayrock.

The large-scale distribution of beachrock in Belize supports the contention that physical processes such as water agitation rather than biological processes control beachrock formation and distribution. Only on windward sides of cays that are close to the reef crest, where large amounts of seawater flush the beaches, considerable amounts of cements can be precipitated to produce beachrock. Cayrock forms due to cementation in the vadose zone and is only preserved on larger, stable mangrove-sand cays.     

Regional spatial distribution of multiple elements in the surface sediments of the eastern Tsushima Strait (southwestern Sea of Japan)

A total of 402 coastal sea-sediment samples were collected from the continental shelf, slope, and basin off Tsushima Island in the western Sea of Japan, and were analyzed for 51 elements as part of a nationwide marine geochemical mapping project. The samples were compared to potentially related sample sets, and the results were considered from the viewpoint of the origin of marine surface sediments in the western Sea of Japan. The spatial distribution of elemental concentrations in the coastal sea sediments correspond to texture, grain size, the presence of shells and foraminifera, and the mud content of surface marine sediments. Most elemental concentrations increased with increasing mud content. Some samples located in littoral areas included sediment particles apparently supplied from nearby rivers, but their contribution was limited. Overall, the mean chemical compositions of clastic material in coastal sea sediments appear to differ from those of stream sediments in adjacent terrestrial areas. In addition, the geochemistry of the coastal sea sediments cannot be fully explained by the mixing of the material supplied from Korean and Chinese stream sediments, which are the most feasible sources. Coastal sea sediments in the study area are well mixed by transportation processes; therefore, elemental abundances in these marine sediments may be homogenized to such an extent that it is not possible to determine their origin. Alternatively, most of the clastics in the sediment may actually represent relict reworked material, originally formed in the Yellow Sea and Tsushima Strait during the last glacial stage and subsequent transgression.     

Yria (western Naxos island,Greece): Sea level changes in Upper Holocene and palaeogeographical reconstruction

The Saint Georgios coastal zone, located at the W coast of Naxos, the largest island of the Central Aegean Sea, was investigated in order to determine the palaeo-geography, sea level changes and their effect to the palaeo-environment of western Naxos island and to human activity. Detailed geomorphological mapping, study of micropaleontological and sedimentological characteristics and dating analyses of the Late Holocene of St. Georgios coastal zone were conducted.

To obtain information about the Holocene stratigraphy under the recent alluvial cover, three boreholes followed the detailed geomorphological mapping. Microfaunal analysis took place and five samples of plants, shells, peat and charred material were also collected from several layers of the sedimentary sequence and were dated using AMS and conventional radiocarbon techniques providing temporal control of the sediments. The sea-land interactions during Upper Holocene, in relation to the eustatic sea level oscillations, as well as the geomorphologic observations and analysis on deposited sediments, aims to reveal the palaeo-geographic evolution of the landscape and its impact on the archaeological sites. Sea level rise along with sea-land interactions to the landscape evolution and the transgression of sea in 6144 BP have been verified.     

Elemental distribution of coastal sea and stream sediments in the island-arc region of Japan and mass transfer processes from terrestrial to marine environments

A total of 49 elements have been identified in 338 coastal sea sediment samples collected from an area situated off the Ise-Tokai region of Japan for a nationwide marine geochemical mapping project. The spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define the natural geochemical background variation, mass transport, and contamination processes. The elemental concentrations of coastal sea sediments are determined primarily by particle size and regional differences. Most elemental concentrations increase with a decrease in particle size. Some elements such as Ca, Mn, and Yb are found to exist in large quantities in coarse particles containing calcareous shells, Fe–Mn oxides, and felsic volcanic sediments. Regional differences reflect the mass transfer process from terrestrial areas to coastal seas and the influence of the local marine geology. An analysis of variance (ANOVA) reveals that for many elements, the particle size effect is predominant over regional difference. The mean chemical compositions of coastal sea sediments are similar to those of stream sediments in adjacent terrestrial areas and in the upper crust of Japan. This observation supports the fact that coastal sea sediments have certainly originated from terrestrial materials. However, the spatial distributions of elemental concentrations are not always continuous between the land and coastal seas. The scale of mass movement observed in marine geochemical maps occurs at a distance of 20 km from the river mouth. A detailed examination of the spatial distribution patterns of K (K₂O) and Cr concentrations suggests that terrestrial materials supplied through rivers are deposited near the shore initially, and then gravity-driven processes shift the sediments deeper into the basin. Contamination with heavy metals such as Zn, Cd and Pb was observed in coastal bays surrounded by urban and industrial areas. It is noteworthy that the areas with the highest concentration of these elements usually do not occur near the shore (not near the contamination source) but at the center of the bay. Unexpected low concentrations of Zn, Cd and Pb near shore may either be due to a decreased anthropogenic load in the most recent sediments or to dilution by unpolluted flood sediments.     

Distribution of arsenic and mercury in subtropical coastal beachrock,Gulf of Mannar,India

An assessment of coastal pollution was made on the basis of trace element concentrations (arsenic — As, mercury — Hg) in the Gulf of Mannar. The beachrock samples were collected along the coastal tracts between Rameswaram and Kanyakumari. The samples were dried and digested to determine the As and Hg using atomic absorption spectrophotometer (AAS-air-acetylene and nitrous oxide method). The As and Hg accumulation status of the beachrock was assessed using geo-accumulation index values (I _geo). The accumulation of As and Hg in the beachrock ranges from 2.75 to 20.72 μg g⁻¹ and from 0.06 to 0.31 μg g⁻¹, respectively. The As and Hg concentrations in the beachrocks are compared with crustal average values and average of other region sediments. The possible source of the contamination is from atmospheric deposition and anthropogenic activities.     

Regressive diagenesis in Pleistocene eolianites from Fuerteventura, Canary Islands

Evidence from a Late Pleistocene eolianite in Fuerteventura, Canary Islands, demonstrates that red algal clasts replaced by low-magnesian calcite in the subaerial environment show a partial re-constitution of their original high-magnesian calcite mineralogy when they are exposed subsequently to sea water. This process only affects the cell walls of the red algae, which, owing to their specific microarchitecture (extremely small crystal size, very large specific surface area), offer the most favourable conditions for dissolution-reprecipitation or diffusion processes. High-magnesian caicite precipitated as a second generation cement on fresh water calcitic cement is an equivalent of the high-magnesian calcite cement which at many locations on the island leads to the formation of beachrock in Holocene intertidal sediments.     

山东半岛东北部全新统研究新进展

全新世以来山东半岛东北部沿岸的相对海面（基准面）变化控制了入海河流河谷内全新统的发育,并通过影响进入海岸带碎屑物质的类型与数量,深刻影响了海岸带全新统的发育。全新世早期（１０～６ｋａ Ｂ． Ｐ．）快速的相对海面上升导致河谷溯源堆积,河流输沙中的推移质均堆积于河谷中,仅有悬移质进入海岸带堆积,因而海岸全新统下部均为细粒的海湾、湖、沼泽相沉积。全新世中期（６～４ｋａ Ｂ．Ｐ．）时海面虽已相对稳定,但早期基准面上升导致的河谷堆积作用仍在进行,因而中全新统的粗碎屑海岸沉积均为源于基岩海岸侵蚀的含贝壳砂砾石。从全新世后期（４ｋａ Ｂ．Ｐ．以来）开始有较丰富的河流推移质输沙进入海岸带,但由于不同规模河流对相对海面变化的地貌响应有显著差别,不同河流对海岸全新统发育的影响各不相同。上述结论为精确地解释低序列、小尺度地层层序提供了理论依据     

闽南、粤东海岸带沉积物的沉积学、岩石学比较研究

本文通过对海岸带海滩砂、沙丘砂、砂丘岩、海滩岩和有关近岸海底砂的沉积学,岩石学的比较研究,分析其形成环境,发现沙丘岩沉积特征和历史沙丘相似;沙丘岩和海滩岩的识别有时不是主要从岩石学而可能从沉积学中去识别。兄弟屿比西海底硬地更可能是生物排出的钙质粘液胶结。     

涠洲岛北港海滩岩的铀系年代及其海平面指示意义

海滩岩是古海平面高程的重要标志。本文利用高精度铀系测年技术对北部湾涠洲岛北港海滩岩中保存完好的珊瑚枝进行了测年,得出珊瑚枝的年龄分布范围介于距今(2017 A.D.) 1780～836年,表明涠洲岛北港海滩岩是晚全新世时期的产物。电子探针元素含量分析得出该海滩岩的胶结物是低镁方解石,其成岩环境为大气淡水环境,但相对高含量的锶则指示其成岩过程中经历了海水的冲刷作用。综合铀系年代、海滩岩的高程及邻近区域的古海平面数据,涠洲岛北港晚全新世时期的海滩岩指示出距今1780～836年海平面高于现今海平面约为0.91～1.16 m,为晚全新世时期高海平面提供了新的信息。     

Submerged upper Holocene beachrock on San Salvador Island,Bahamas: implications for recent sea-level history

Sedimentological, petrographic and radiometric data from a submerged beachrock on San Salvador Island, Bahamas, provide new information about the Late Holocene sea-level history in this area.At French Bay, on the southern shore of the island, samples of beachrock collected at a depth of 1 m below low tide level yielded an average ¹⁴C age of 965 ± 60 years before present. These samples further display a well developed fenestral porosity and present an early generation of low Mg calcite meniscus cement. These features characterize intertidal and supratidal settings; they are not consistent with the present beachrock position and the reported Late Holocene sea-level history in the Bahamas. A 1.5–2m low stand of the sea about 1000 years ago would best explain the observed particularities of the French Bay beachrock.This example from San Salvador shows that the smooth trend of Late Holocene sea-level rise proposed by previous workers might be overprinted by high frequency, low amplitude fluctuations. Recognition of these fluctuations is fundamental when calculating rates of sea-level rise and evaluating the coastal response to a marine transgression. Correspondence to: P. Kindler     

Construction of an evolutionary deglaciation model for the Irish midlands based on the integration of morphostratigraphic and geophysical data analyses

Alternative, established models for the deglaciation of the midlands of Ireland are tested against an interpretation of a suite of deglacial sediments covering an area of 600 km² in the east central midland area. Interpretation of the sediments is based on geomorphological mapping, lithostratigraphic characterization of exposures and geotechnical data supported by electrical resistivity tomography (ERT) and ground penetrating radar (GPR). GPR depicted small‐scale sedimentological and deformational structures within low‐conductivity soft sediments, such as cross‐bedding, planar bedding, channel‐like features and faulting planes, and revealed the internal architecture of eskers, glaciodeltas, subaqueous fans and raised bogs. ERT data permitted the detection of depth to bedrock and the lithological characterization of unconsolidated sediments. The ten sites presented were surveyed by traditional mapping methods and/or geophysical techniques. This allowed the construction of a local model of the deglaciation of the area which recognized five main stages. An ice sheet covering most of Ireland withdrew as a single body as far as the midlands. At this stage, two main directions of ice retreat are identified from the spatial distribution of meltwater/overflow channels, esker and morainic ridges, and ice‐marginal glaciolacustrine deposits. A pattern of deglacial sedimentation into an expanding ice‐marginal glacial lake is depicted. The glacial lake was dammed to the west by two ice dome fronts, one decaying to the north‐west and another to the south‐west, and by the Shannon Basin watershed to the east. Glacial lake outlets identified along the watershed and the altitude of the topset/foreset interface zone depicted in glaciodeltaic deposits allowed the identification of three lake water levels. The highest level is at 87–89 m Ordnance Datum (OD), the second lake level at 84 m OD and the third at 78 m OD. Copyright © 2012 John Wiley & Sons, Ltd.     

Factors controlling regional spatial distribution of 53 elements in coastal sea sediments in northern Japan: Comparison of geochemical data derived from stream and marine sediments

In all, 53 elements were analyzed in 1406 coastal sea sediment samples collected from an area off Hokkaido and the Tohoku region of Japan during a nationwide marine geochemical mapping project. The spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define natural geochemical background variation and mass transport processes. The terrestrial area is covered by mafic volcanic rocks and accretionary complexes associated with ophiolite, which has small amounts of felsic volcanic rocks and granite. The spatial distribution patterns of elements enriched in mafic lithologies such as Fe (Total Fe₂O₃) and Sc in marine environments are influenced by adjoining terrestrial materials. The spatial distribution patterns of Cr and Ni concentrations, which are highly abundant in ultramafic rocks on land, are used to evaluate the mass transport from land to the sea and the dispersive processes caused by oceanic currents. The scale of mass transport by oceanic currents occurs up to a distance of 100–200 km from the coast along the coastal areas. The regional differences of elements rich in felsic lithologies such as K (K₂O), Nb and La in marine sediments are determined mainly by the relative proportion of minerals and lithic fragments enriching felsic materials to those associated with mafic materials. The spatial distribution of elemental concentration is not always continuous between the land areas and coastal sea areas. That difference is interpreted as resulting from (1) transportation of marine sediments by oceanic currents and storm waves, (2) contribution of volcanic materials such as tephra, (3) occurrence of shell fragments and foraminifera tests and (4) distribution of relict sediments of the last glacial age and early transgression age. Contamination with Cu, Zn, Cd, As, Mo, Sn, Sb, Hg, Pb and Bi was not observed in marine environments because the study area has little anthropogenic activity. Terrestrial materials are the dominant source for these metals. The Mo, Cd, Sn, Sb, Hg, Pb and Bi are abundant in silty and clayey sediments locally because of early diagenetic processes, authigenic precipitation and organic substances associated with these elements. The spatial distribution of As concentration shows exceptions: it is concentrated in some coarse and fine sands on the shelf. The enrichment is explained by adsorption of As, sourced from a coal field, to Fe hydroxide.     

海岸带地质工作中陆海统筹的方法论探讨

陆海统筹是我国海岸带地质工作的重要方向,但以往的海岸带地质工作通常按陆区和海区分别开展,对如何实现陆海统筹没有形成统一认识.上海作为我国率先开展海岸带地质工作的地区之一,在陆海统筹方面进行了一些有益尝试,积累了一定经验.基于这些实践经验,并结合国内外海岸带地质工作现状,对海岸带地质工作中陆海统筹的方法论进行了探讨,提出了海岸带地质工作中陆海统筹应包含陆海成果一体化和以水体为媒介实现陆海联动的两个基本要求.研究认为:在外业工作部署上,应发挥陆区河流和海区海岛的中介作用,着眼于区域性而非局部地区的地质成果编制;在地质环境监测上,以海堤或岸线为纽带对陆区和海区进行同步监测;在成果图件编制上,为实现陆海成果的有机整合,统一陆海数据标准是关键,在保存数据科学信息的前提下适当简化数据等级的分类.     

莱州湾海洋沉积物粒度特征及其环境响应分析

基于20个柱状样粒度信息,文章对山东莱州湾海域1~3 m厚度的沉积环境展开了研究。莱州湾海域沉积物粒度组分以砂质和粉砂质为主,整体上分选性偏差,在沉积过程中受周边环境改造明显。莱州湾海洋沉积动力环境在粒度方面有较好的响应,柱状样粒度分布图反映不同海域沉积物所处的外力作用阶段各有不同,但总体上随着搬运距离增大,至中部浅海平原,概率累积曲线斜率逐渐变大,阶段分化愈发明显。莱州湾浅部海域共同环境敏感组分为3≤φ≤4,沿岸河流性质和泥沙输运路径对粒度组分影响明显。综合前人关于沉积速率的研究成果,表明莱州湾东部海域粒度组分阶段性变化与1855年黄河改道在时间上存在一定的对应关系。就沉积物形成环境而言,莱州湾中部海域沉积环境水动力较强,物质来源多样。屺坶岛—刁龙嘴海域沉积物的颗粒略粗,需要的临界起动速度较大,发生再悬浮的几率相对较小。黄河水下三角洲沉积环境比较动荡,能量不稳定,处于重力流后期,能量衰减并向牵引流转化。南部的水下岸坡在波浪、潮流作用下有一定量的泥沙淤积。     

Sediment provenance of the Wilderness barrier dunes,southern Cape coast,South Africa

Trace‐element geochemistry has been used to discern the provenance of sediments derived from geologically distinct sources found in a range of depositional settings. This study investigates whether this approach can also identify provenance signatures in sediments derived from clastic sedimentary rocks of similar origins, within a complex coastal transport environment. The potential local sediment sources of a coastal barrier dune in South Africa were analysed to assess their relationships with the barrier and whether these have varied with time. Results indicate that the oldest part of the barrier, partly formed during MIS 6 when sea levels were lower than at present, has a closer affinity to fluvial sediment provided by local rivers than either younger samples from the barrier′s seaward flank or the Holocene dunes atop its crest, both formed during sea‐level highstands. Constraints on the timing of barrier formation provided by OSL dating proved helpful in discriminating between provenance and weathering signals. Terra Nova, 00, 000–000, 2010     

Coastal geoindicators of environmental change in the humid tropics

The primary geoindicators appropriate for monitoring environmental changes in the humid tropics are transitory surface water levels, shoreline position, wetlands distribution, coral reefs, landforms, and sediment sequence and composition. Lateral zonations and temporal successions of vegetation also can be used as geoindicators of riverine and shoreline changes. All of these coastal geoindicators are sensitive to regional tectonic processes and anthropogenic alterations and they typically reflect significant changes in coastal conditions such as fluvial processes, coastal energy, water quality, relative sea level, and sediment supply. Where humid tropical coasts coincide with active tectonic margins, indicators of seismic activity are critical to understanding coastal changes associated with co-seismic subsidence or uplift, tsunamis, and liquefaction of coastal sediments. Coastal landforms and sedimentary deposits that record late Quaternary environmental changes include perched fluvial and marine terraces, delta-plain morphologies, crevasse-splay deposits, peats and other paleosols, beach ridges, mud capes, and mud volcanoes. Although these features and deposits typically reflect environmental changes spanning more than 100 years, they are relevant to modern processes, management of coastal lands and resources, and prediction of future conditions. In some regions of the humid tropics, large coastal areas are unaffected by hurricanes or typhoons. Nevertheless, these tropical coasts are vulnerable to other non-storm processes, such as El Niño events, tsunamis, and monsoons that increase water levels, and cause widespread flooding and beach erosion. The environmental and political significance of coastal geoindicators increases when they are integrated and applied to issues of human safety and health such as hazards mapping, risk assessment, and dispersion of contaminated sediments. However, to be relevant, those socio-environmental applications demand accurate predictions of future trends and rates of change.     

富集培养条件下湖泊和沿海海域水体硫酸盐还原菌的耐氧性特征

硫酸盐还原菌（sulfate-reducing bacteria,SRB） 是一类兼性厌氧菌,在湖泊和海洋有机物矿化过程和生物源性黄铁矿 的生成过程中都扮演着重要角色。环境溶解氧浓度对硫酸盐还原过程影响较大,硫酸盐还原菌在水体中的耐氧性是目前的研 究热点。文章采集了象山港和水口水库不同溶解氧水平下的水样,并在相应的溶解氧梯度下进行富集培养,以探讨不同溶解 氧浓度下硫酸盐还原菌的耐氧性特征及硫代谢相关菌的组成。结果显示,在富集培养条件下湖泊和沿海海域中Desulfovibrio （脱硫弧菌属） 和Desulfomicrobium （脱硫微菌属） 为主要硫酸盐还原细菌,而Shewanella （希瓦氏菌属） 和Sulfurospirillum （硫小螺体属） 为其硫代谢相关菌。Desulfovibrio的相对丰度与溶解氧水平密切相关,随溶解氧浓度的减少,其相对丰度增加。 SRB 的耐氧上限为6.68 mg/L,明显高于以往纯培养或共培养的耐氧上限值。作者推测这不仅与其高氧环境的适应策略有关, 还可能得益于共存菌的贡献,后者可能通过消耗环境中的氧为Desulfovibrio提供生态位,提高其耐氧水平。     

富集培养条件下湖泊和沿海海域水体硫酸盐还原菌的耐氧性特征

硫酸盐还原菌（sulfate-reducing bacteria，SRB） 是一类兼性厌氧菌，在湖泊和海洋有机物矿化过程和生物源性黄铁矿 的生成过程中都扮演着重要角色。环境溶解氧浓度对硫酸盐还原过程影响较大，硫酸盐还原菌在水体中的耐氧性是目前的研 究热点。文章采集了象山港和水口水库不同溶解氧水平下的水样，并在相应的溶解氧梯度下进行富集培养，以探讨不同溶解 氧浓度下硫酸盐还原菌的耐氧性特征及硫代谢相关菌的组成。结果显示，在富集培养条件下湖泊和沿海海域中Desulfovibrio （脱硫弧菌属） 和Desulfomicrobium （脱硫微菌属） 为主要硫酸盐还原细菌，而Shewanella （希瓦氏菌属） 和Sulfurospirillum （硫小螺体属） 为其硫代谢相关菌。Desulfovibrio的相对丰度与溶解氧水平密切相关，随溶解氧浓度的减少，其相对丰度增加。 SRB 的耐氧上限为6.68 mg/L，明显高于以往纯培养或共培养的耐氧上限值。作者推测这不仅与其高氧环境的适应策略有关， 还可能得益于共存菌的贡献，后者可能通过消耗环境中的氧为Desulfovibrio提供生态位，提高其耐氧水平。