Seismic geomorphology and growth architecture of a Miocene barrier reef,Browse Basin,NW-Australia

The Cenozoic succession of Browse Basin is characterized by a carbonate system, that developed from a non-tropical ramp in Eocene-lower Miocene times to a tropical rimmed platform in the middle Miocene. The evolution of the platform was unraveled through the interpretation of the seismic geomorphology and borehole data of the middle Miocene tropical reef system. The first reef structures developed during the early middle Miocene as narrow linear reef belts with an oblique orientation with respect to shelf strike direction. Subsequently, they prograded toward the platform margin to form a barrier reef with a minimum length of 40 km. The barrier reef itself comprises three distinct ridges separated by progradational steps. The second and third step are separated by a karstified horizon, which is interpreted to represent the global sea-level fall shortly before the Serravallian/Tortonian boundary. The following third ridge formed in a slightly downstepped position during the sea-level lowstand and initial transgressive phase. Further sea-level rise during the early Tortonian first drowned the barrier-reef system and subsequently also the patch reefs and relic atolls that had established in a backstepped position in the platform interior. The similar evolution of the Browse Basin reef system and other contemporaneous carbonate systems indicates a strong impact of eustatic sea-level changes. Relatively large subsidence rates in the study area possibly augmented the eustatic sea-level rise in the Tortonian and hence contributed to the drowning of the reef system. However, the initiation and final demise of the reef system was also governed by global and regional climate variations. The first seismically-defined reefs developed simultaneous to a maximum in the transport capacity of the Indonesian throughflow, which brings warm low-salinity waters to the North-West Shelf. Reef drowning followed the restriction of this seaway close to the middle to early Miocene boundary. This near closure of the Indonesian seaway possibly led to a regional amplification of the global middle to late Miocene cooling trend and hampered the potential of the reef system to keep up with the rising sea-level.     

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.     

Microbialite development patterns in the last deglacial reefs from Tahiti (French Polynesia; IODP Expedition #310): Implications on reef framework architecture

The widespread occurrence of microbialites in the last deglacial reef frameworks (16–6 Ka BP) implies that the accurate study of their development patterns is of prime importance to unravel the evolution of reef architecture through time and to reconstruct the reef response to sea-level variations and environmental changes.The present study is based on the sedimentological and chronological analysis (¹⁴C AMS dating) of drill cores obtained during the IODP Expedition #310 “Tahiti Sea Level” on the successive terraces which typify the modern reef slopes from Tahiti. It provides a comprehensive data base to investigate the microbialite growth patterns (i.e. growth rates and habitats), to analyze their roles in reef frameworks and to reconstruct the evolution of the reef framework architecture during sea-level rise.The last deglacial reefs from Tahiti are composed of two distinctive biological communities: (1) the coralgal communities including seven assemblages characterized by various growth forms (branching, robust branching, massive, tabular and encrusting) that form the initial frameworks and (2) the microbial communities developed in the primary cavities of those frameworks, a few meters (1.5 to 6 m) below the living coral reef surface, where they heavily encrusted the coralgal assemblages to form microbialite crusts. The dating results demonstrate the occurrence of two distinctive generations of microbialites: the “reefal microbialites” which developed a few hundred years after coralgal communities in shallow-water environments, whereas the “slope microbialites” grew a few thousands of years later in significantly deeper water conditions after the demise of coralgal communities.The development of microbialites was controlled by the volume and the shape of the primary cavities of the initial reef frameworks determined by the morphology and the packing of coral colonies. The most widespread microbialite development occurred in frameworks dominated by branching, thin encrusting, tabular and robust branching coral colonies which built loose and open frameworks typified by a high porosity (> 50%). In contrast, their growth was minimal in compact coral frameworks formed by massive and thick encrusting corals where primary cavities yielded a low porosity (~ 30%) and could not host a significant microbialite expansion.     

Carbonate slope morphology revealing sediment transfer from bank-to-slope (Little Bahama Bank,Bahamas)

New high-quality multibeam and high-resolution seismic data reveal new observations on sediment transfer and distribution and margin morphometrics in the uppermost slope of Northeastern Little Bahama Bank between 20 and 300 m water depth. The echofacies/backscatter facies show an alongslope sediment distribution forming successive strips. The upper part of the uppermost slope corresponds to the alternation of several submerged coral terraces and escarpments that could be related to Late Quaternary sea-level variations. The terraces could either be related to periods of stagnating sea-level or slow-down in sea-level change and therefore increased erosion by waves, or periods of accelerated sea-level rise since the Last Glacial Maximum. Terraces could therefore be related to coral construction and drowing. The medium part corresponds to the marginal escarpment, a steep cemented area. The lower part of the uppermost slope shows a discontinuous Holocene sediment wedge with varying thickness between 0 and 35 m. It is separated from the upper part by a zone of well-cemented seafloor associated with the marginal escarpment. Passing cold fronts result in sediment export caused by density cascading. The associated sediment fall-out and convective sedimentation can generate density currents that form this wedge and eventually flow through linear structures on the upper slope. The survey reveals the presence of recently active channels that extend over the entire uppermost slope and interrupt the wedge. The channels connect shallow tidal channels to submarine valleys connected to the proximal part of canyons. They directly feed the canyons with platform-derived sediment forming low-density turbidity currents and could supply the deepest part of the system with coarse-grained sediment directly exported from the carbonate platform.     

Drowned coralline algal dominated deposits off Lanai,Hawaii; carbonate accretion and vertical tectonics over the last 30 ka

We present detailed bathymetry, remotely operated vehicle (ROV) and submersible observations, and sedimentary and radiocarbon age data from carbonate deposits recovered from two submerged terraces at − 150 m (T1) and − 230 m (T2) off Lanai, Hawaii. The tops of the terraces are veneered by relatively thin (< 5 m) in situ accumulations of coralline algal nodule, coralgal nodule, Halimeda and a derived oolitic facies deposited in intermediate (30–60 m) to deep fore-reef slope settings (60–120 m). The data are used to develop a sedimentary facies model that is consistent with eustatic sea-level variations over the last 30 ka. Both nodule facies on T1 and T2 initiated growth 30–29 ka following a fall in sea level of ∼50 m and increase in bottom currents during the transition from Marine Isotope Stage 3 to 2. The nodules accreted slowly throughout the Last Glacial Maximum when sea-level was relatively stable. Drowning occurred during the early deglaciation (17–16 ka) and was marked by the complete drowning of coralline algal nodules facies on T2 and incipient drowning of coralgal facies on T1. Abrupt sea-level rise during the middle deglaciation, perhaps associated with global meltwater pulse 1A (14–15 ka), finally drowned the coralgal facies on T1, which in turn was overlain by a deep-water Halimeda facies or an oolitic facies derived from upslope. Our data indicates that Lanai has experienced relatively little vertical tectonic movement over the last 30 ka. Using paleobathymetric data derived from the sedimentary facies, age vs. depth relationships, and published sea-level curves, we estimate that Lanai could be either slowly uplifting or subsiding, but at rates < 0.1 m/kyr (uplift) or < 0.4 m/kyr (subsidence) over this 30 kyr period.     

Late Holocene sea-level rise in Tampa Bay: Integrated reconstruction using biomarkers,pollen, organic-walled dinoflagellate cysts,and diatoms

A suite of organic geochemical, micropaleontological and palynological proxies was applied to sediments from Southwest Florida, to study the Holocene environmental changes associated with sea-level rise. Sediments were recovered from Hillsborough Bay, part of Tampa Bay, and studied using biomarkers, pollen, organic-walled dinoflagellate cysts and diatoms. Analyses show that the site flooded around 7.5 ka as a consequence of Holocene transgression, progressively turning a fresh/brackish marl-marsh into a shallow, restricted marine environment. Immediately after the marine transgression started, limited water circulation and high amounts of runoff caused stratification of the water column. A shift in dinocysts and diatom assemblages to more marine species, increasing concentrations of marine biomarkers and a shift in the Diol Index indicate increasing salinity between 7.5 ka and the present, which is likely a consequence of progressing sea-level rise. Reconstructed sea surface temperatures for the past 4 kyrs are between 25 and 26 ° C, and indicate stable temperatures during the Late Holocene. A sharp increase in sedimentation rate in the top ∼50 cm of the core is attributed to human impact. The results are in agreement with parallel studies from the area, but this study further refines the environmental reconstructions having the advantage of simultaneously investigating changes in the terrestrial and marine environment.     

Mass culturing of living sands (Baculogypsina sphaerulata) to protect island coasts against sea-level rise

Coral reef islands have a self-sustaining mechanism that expands and maintains the islands through the deposition of calcium carbonate (CaCO₃) by marine organisms. However, the human societies established on such low-lying coral reef islands are vulnerable to rapid sea-level rises. Enhancing the self-sustaining mechanism of coral reefs will become one of the required sustainable countermeasures against sea-level rise. We examined the feasibility of mass culturing the large benthic foraminifera Baculogypsina sphaerulata, which is known as “living sand.” We developed a rearing system with the key components of an artificial lawn as a habitat and a stirring device to create vertical water currents. Batches of B. sphaerulata in two different size groups were reared to examine size growth and reproduction under the culture conditions. All culture batches reproduced asexually following generations over 6 months in culture. The small-sized group exhibited steady growth, whereas the large-sized group underwent a reduction in mean size because large individuals (> 1.5 mm²) died off. Similar traits of size structure between the culture batches and natural populations indicate that our culturing conditions can successfully reproduce environments similar to the habitat of this species. Reproduction, consistent size growth, and size structure similar to the natural population indicate that the examined rearing system is viable for culturing Foraminifera at a large scale.     

晚更新世以来南黄海中部进积体序列与古河流系统

通过高分辨率浅地层剖面声学地层与钻孔沉积地层的综合对比分析,系统研究了晚更新世以来南黄海中部海域的层序地层序列及其对海平面变化的响应。研究显示,基于高分辨率浅地层剖面自老至新划分的6个声学地层单元（U5、U4、U3、U2、U1-2、U1-1）与钻孔划分的沉积地层单元密切相关。MIS4期与末次冰盛期低海面时期发育的2个层序界面（R4、R2）,将研究区晚更新世以来的层序地层自下而上划分为3个层序（SQ3、SQ2、SQ1）,并识别出3期进积体序列与2期古河流系统。MIS5期与MIS3期高海面及海平面下降期间的2期东向进积体序列主要包括高位体系域与强制海退体系域,对应浅海—滨海沉积,厚度分别由西部的24 m与40 m向东明显变薄,而全新世高海面以来向海的进积体序列主要对应高位体系域,与长江源的浅海相泥质沉积相关,最大厚度超过16 m。研究区MIS4期和末次冰盛期发育的2期古河流系统与低位体系域相对应,最大沉积厚度分别超过36 m与24 m,均与长江及黄河密切相关,影响范围延伸至黄海槽及其以东海域,尤其末次冰盛期最远可达济州岛附近海域。     

Late Quaternary siliciclastic/carbonate sedimentation model for the Capricorn Channel,southern Great Barrier Reef province,Australia

A model is presented for hemipelagic siliciclastic and carbonate sedimentation during the last glacial–interglacial cycle in the Capricorn Channel, southern Great Barrier Reef (GBR). Stable isotope ratios, grainsize, carbonate content and mineralogy were analysed for seven cores in a depth transect from 166 to 2892 m below sea level (mbsl). Results show variations in the flux of terrigenous, neritic and pelagic sediments to the continental slope over the last sea level cycle.During the glacial lowstand terrigenous sediment influenced all the cores down to 2000 mbsl. The percentages of quartz and feldspar in the cores decreased with water depth, while the percentage of clay increased. X-ray diffraction analysis of the glacial lowstand clay mineralogy suggests that the siliciclastic sediment was primarily sourced from the Fitzroy River, which debouched directly into the northwest sector of the Capricorn Channel at this time. The cores also show a decrease in pelagic calcite and an increase in aragonite and high magnesium calcite (HMC) during the glacial. The influx of HMC and aragonite is most likely from reworking of coral reefs exposed on the continental shelf during the glacial, and also from HMC ooids precipitated at the head of the Capricorn Channel at this time. Mass accumulation rates (MARs) are high (13.5 g cm^? 3 kyr^? 1) during the glacial and peak at ~ 20 g cm^? 3 kyr^? 1 in the early transgression (16–14 ka BP). MARs then decline with further sea level rise as the Fitzroy River mouth retreats from the edge of the continental shelf after 13.5 ka BP. MARs remain low (4 cm^? 3 kyr^? 1) throughout the Holocene highstand.Data for the Holocene highstand indicate there is a reduction in siliciclastic influx to the Capricorn Channel with little quartz and feldspar below 350 mbsl. However, fine-grained fluvial sediments, presumably from the Fitzroy River, were still accumulating on the mid slope down to 2000 mbsl. The proportion of pelagic calcite in the core tops increases with water depth, while HMC decreases, and is present only in trace amounts in cores below 1500 mbsl. The difference in the percentage of HMC in the deeper cores between the glacial and Holocene may reflect differences in supply or deepening of the HMC lysocline during the glacial.Sediment accumulation rates also vary between cores in the Capricorn Channel and do not show the expected exponential decrease with depth. This may be due to intermediate or deep water currents reworking the sediments. It is also possible that present bathymetry data are too sparse to detect the potential role that submarine channels may play in the distribution and accumulation of sediments.Comparison of the Capricorn Channel MARs with those for other mixed carbonate/siliciclastic provinces from the northeast margin of Australia indicates that peak MARs in the early transgression in the Capricorn Channel precede those from the central GBR and south of Fraser Island. The difference in the timing of the carbonate and siliciclastic MAR peaks along the northeast margin is primarily related to differences in the physiography and climate of the provinces. The only common trend in the MARs from the northeast margin of Australia is the near synchronicity of the carbonate and siliciclastic MAR peaks in individual sediment cores, which supports a coeval sedimentation model.     

New evidence for drowned shelf edge reefs in the Great Barrier Reef,Australia

We present four new high-resolution multibeam bathymetry datasets from the shelf edge of the northern Great Barrier Reef (GBR). Analysis of these data, combined with Chirp sub-bottom profiles and existing submersible observation data provides a fresh insight into the detailed morphology and spatial distribution of submerged reefs and terraces at the shelf edge. An extensive and persistent line of drowned shelf edge reefs exist on the GBR margin in about 40 to 70 m. They appear as barrier reefs up to 200 m wide and comprising twin parallel ridges of rounded pinnacles. Subtle yet consistent terrace and step features lie between 78 and 114 m seaward of the shelf edge reefs in the southern study area. Submersible observations confirm that the drowned reefs now provide a favorable hard substrate for live soft corals and algae. They form a consistent and extensive seabed habitat that extends for possibly 900 km along the GBR shelf edge. The submerged reef and terraces features may reflect a complex history of growth and erosion during lower sea-levels, and are now capped by last deglaciation reef material.     

Future sea-level rise and its early detection by satellite remote sensing

During the past 100 years, sea-level appears to have risen by 10–15cm, probably due to the combined effects of thermal expansion of ocean-surface waters and net melting of glaciers and ice caps, associated with a small increase in global temperatures. This trend will almost certainly continue and accelerate if steadily increasing levels of carbon dioxide and other “greenhouse” gases in the atmosphere cause warming of the magnitude widely predicted by climate modellers. Rising air temperatures will cause increased melting from glaciers and ice caps, and rising sea-water temperatures will cause thermal expansion of the oceans. Moreover, warmer ocean waters could melt and weaken the many floating ice shelves that surround Antarctica, permitting increased ice discharge from glaciers that flow into them. All of these factors would cause sea-level to rise, and this paper presents and estimate of the total sea-level rise that could occur during the next century.If, as predicted by many climate models, global temperatures increase by an average of about 3°C, there is a good probability that sea-level will rise approximately 1m by the year 2100. Ultimately, such a rise would become very apparent to coastal populations, but initial change would be slow. Consequently, it is important to devise and “early warning system” for prompt detection of changes that will precede a detectable rise in sea level. These include: surface temperatures on land, oceans and ice sheets; sea-ice distribution; extent of summer melting on the polar ice sheets; areal extent and surface elevations of the ice sheets in Greenland and Antarctica. All of these parameters can be measured from space by satellites that are operating now or are planned for launch during the next few years     

Hawaiian submarine terraces,canyons, and Quaternary history evaluated by seismic-reflection profiling

The numerous submarine and elevated terraces that fringe shorelines of the Hawaiian Islands have been used as classic examples of mid-ocean Quaternary eustatic terraces. Submarine canyons are important geomorphic features of island slopes. Later reef growth often partly masks both the terraces and canyons. Although difficult to match from one side of an island to the other, some of the terraces have been correlated to successions of higher and lower Quaternary sea levels determined elsewhere in the world. Subbottom seismic reflection profiling now permits a new view of the problem, especially as related to the most recent marine history of Oahu. The geophysical work allows a partial deciphering of former terraces, now buried by younger reefs and sand, and at the same time shows that the heads of submarine canyons do connect with subaerial valleys beneath the succession of Quaternary nearshore deposits. However, the work has disclosed so many additional buried terraces as to raise serious doubts whether it will be possible, without improved techniques of dating the deposits themselves, to unravel the history of Quaternary sea-level changes in Hawaii, much less to correlate them with events recorded elsewhere.     

南海关键地质历史时期的古海岸线变化

整个南海新生代的演变可概括为一系列微板块在太平洋板块与印度洋板块运动影响下发生拉薄、裂解、滑移、旋转、会聚和碰撞的过程,特别是经过55、33、25、16、6、2 Ma关键时期的演化,最终形成现在具有陆架和深水海盆特征的西太平洋最大边缘海。依据南海内部各坳陷盆地的最新研究进展,包括海相边缘沉积相类型、古水深、钻井资料等能够依次重建南海特殊历史时期的古岸线位置,分析其变迁规律,并与古新世、始新世之交的高温事件,始新世末-渐新世初全球气候变冷事件,渐新世-中新世全球变冷、海平面下降事件,中中新世早期气候回暖、全球海平面上升事件,上新世早期全球变暖事件,晚上新世北极冰盖形成等系列事件进行对比,从而进一步了解古新世以来南海的环境演变过程。     

Key species of hermatypic coral for reef formation in the northwest Pacific during Holocene sea-level change

Cores from Holocene reefs provided a growth history and species-level identification of corals and demonstrated the most important reef builders during the formation stage. This knowledge is important to determine a principle for reef formation and to provide preservation plans in the near future. A biological and sedimentological study of sediment cores recovered from the Palau Islands and Yoron Island, northwest Pacific, revealed four major facies: corymbose Acropora, arborescent Acropora, massive Porites, and detritus. Species-level observations show that arborescent Acropora (A. muricata and A. intermedia) contributed to reef growth under low- to moderate-energy conditions, whereas corymbose and tabular Acropora (A. digitifera, A. hyacinthus, and A. robusta/A. abrotanoides) and I. palifera were key species for reef formation under high-energy conditions during Holocene sea-level rise and the ensuing period of sea-level stability. Once sea level had stabilized, massive Porites became restricted to areas subjected to low-energy, turbid conditions. These key species are successful corals because the ecological strategy is rapid growth, determinate growth, a high degree of colony integration, strongly resistant to wave action, and rapid local dispersion via fragmentation. Moreover, the western boundary current (Kuroshio) flows along the reefs in the northwest Pacific and it is easy for key species to distribute throughout the region during the period of Holocene sea-level rise and stabilization. These features are a principle for reef formation during sea-level changes. These key species played a significant role in Holocene reef formation in the northwest Pacific; however, coral mortality, caused by climate change, has recently been widely reported. Moreover, the decrease in key species abundance in present-day reefs has been more severe than that in any other species. These geological findings have important implications regarding the appropriate use of coral transplantation and decisions regarding the optimal location and size of marine protected areas.     

深海氧同位素第3阶段古气候—海平面变化研究进展

根据近年来的主要研究成果,简要综述了深海氧同位素第3阶段(MIS 3)气候—海平面变化特征及其沉积记录的研究进展。MIS3期间的气候变化是古气候研究中的重要组成部分,该时段的某些气候特征与现今十分类似。取自极地冰心、海洋沉积物和陆地的古气候记录表明,在MIS3阶段全球经历了一系列数百年至千年时间尺度的快速气候突变事件,其成因、机制和影响范围还存在明显的不确定性。利用深海沉积物的氧同位素、珊瑚礁阶地、陆源碎屑沉积记录分析得出的MIS3古海平面高度偏差较大,主要认为在-50~-90 m之间波动,但也有研究表明MIS3海平面可达-15~-20 m。对MIS3古气候和海平面变化的深入研究,有赖于全球范围内更多不同类型和高分辨率的地质记录所提供的证据。     

海南岛鹿回头珊瑚礁研究进展

前人在海南岛鹿回头珊瑚礁区所做的工作主要集中于以下三方面：(1)鹿回头珊瑚礁区地貌的粗略描述;(2)鹿回头珊瑚礁记录的古海平面研究：(3)鹿回头珊瑚礁记录的现代环境信息研究。通过野外实地考察,将鹿回头珊瑚礁分为8个生物地貌带：礁前斜坡活珊瑚带、礁缘砾石突起脊带、外礁坪带、中礁坪带、内礁坪带、海滩、沙堤、洼地,它们是全新世海平呵和气候环境变化的产物。关于本区珊瑚礁的研究,结合全球珊瑚礁与环境的研究来看,许多工作有待于展开和补充,大致可从以下4个方面进行深入研究：(1)珊瑚礁的生物地貌过程;(2)珊瑚及珊瑚礁的高分辨率环境记录;(3)珊瑚对海洋环境污染的记录：(4)珊瑚礁生态系统与社会、经济及人文系统的关系及其可持续发展。     

Relative Sea Level Changes in Maldives and Vulnerability of Land Due to Abnormal Coastal Inundation

Oceanic Islands in the Pacific and Indian Oceans have extremely small land areas, usually less than 500 km2, with maximum height about 4 m above sea level. The Republic of Maldives is an independent island nation in the Indian Ocean south of Sri Lanka which stretches vertically in the Indian Ocean from 07° 06'N - 0° 42'S. The land area of this island country is about 300 km2, and none of Maldives' 1190 islands has an elevation more than 3 m above sea level. In fact the Maldives has the distinction of being the flattest country on earth, making it extremely vulnerable to the effects of global warming. Of the south Asian countries, the Maldives is the most vulnerable nation, facing severe consequences as a result of global warming and sea level rise (SLR). Because of their obvious vulnerability to SLR, the Government of Maldives is very much concerned about climate change. As global warming and the related SLR is an important integrated environmental issue, the need of the hour is to monitor and assess these changes. The present article deals mainly with the analysis of the tidal and Sea Surface Temperature (SST) data observed at Male and Gan stations along the Maldives coast in the northern and southern hemispheres, respectively. The objective of the analysis is to study the trends of these parameters. Trend analysis is also performed on the corresponding air temperature data of both stations. The results show that Maldives coastal sea level is rising in the same way (rising trend) as the global sea level. The mean tidal level at Male has shown an increasing trend of about 4.1 mm/year.Similarly at Gan, near the equator,it has registered a positive trend of about 3.9 mm/year.Sea level variations are the manifestations of various changes that are taking place in the Ocean-Atmosphere system. Therefore, the variations in SST and air temperature are intimately linked to sea level rise. It is found that SST and air temperature have also registered an increasing trend at both stations. The evidence of rising trends suggest that careful future monitoring of these parameters is very much required. Tropical cyclones normally do not affect the Maldives coast. However, due to its isolated location, the long fetches in association with swells generated by storms, that originated in the far south have resulted in flooding. Thus the rising rate of sea level with high waves and flat topography have increased the risk of flooding and increased the rate of erosion and alteration of beaches.     

末次盛冰期巽他大陆北部草本植被扩张

末次盛冰期(Last Glacial Maximum, LGM)全球低海平面时,巽他陆架大面积暴露,其上的植被类型对于生物多样性演化和全球陆地碳储库有重要影响。但目前植被重建结果仍存在很大争议:一种观点认为LGM时巽他陆架主要分布稀树草原植被,雨林只零星存在于少数区域;而一些数值模拟结果和沉积记录显示巽他陆架上不存在大面积跨赤道的稀树草原,雨林植被仍占主导。LGM时巽他大陆北部可靠的植被记录十分有限。本研究依据靠近巽他陆架北部古河流入海口的沉积物岩芯,利用叶蜡烷烃含量和正构烷烃平均链长指标重建LGM时北巽他大陆的植被信息,结果显示平均链长在22～14.5 kaBP期间出现最大值,推测相对于全新世,冰期时巽他大陆北部草本成分增加。海平面降低使得冰期太平洋沃克环流减弱,呈现类厄尔尼诺状态,导致巽他大陆地区干旱加重,特别是赤道外围区域(南北纬7°以外)降水季节性增强,这种气候状态可能是草本植被成分增多的主要因素。     

Erosion of continental margins in the Western Mediterranean due to sea-level stagnancy during the Messinian Salinity Crisis

High-resolution multi-channel seismic data from continental slopes with minor sediment input off southwest Mallorca Island, the Bay of Oran (Algeria) and the Alboran Ridge reveal evidence that the Messinian erosional surface is terraced at an almost constant depth interval between 320 and 380 m below present-day sea level. It is proposed that these several hundred- to 2,000-m-wide terraces were eroded contemporaneously and essentially at the same depth. Present-day differences in these depths result from subsidence or uplift in the individual realms. The terraces are thought to have evolved during one or multiple periods of sea-level stagnancy in the Western Mediterranean Basin. According to several published scenarios, a single or multiple periods of relative sea-level stillstand occurred during the Messinian desiccation event, generally known as the Messinian Salinity Crisis. Some authors suggest that the stagnancy started during the refilling phase of the Mediterranean basins. When the rising sea level reached the height of the Sicily Sill, the water spilled over this swell into the eastern basin. The stagnancy persisted until sea level in the eastern basin caught up with the western Mediterranean water level. Other authors assigned periods of sea-level stagnancy to drawdown phases, when inflowing waters from the Atlantic kept the western sea level constant at the depth of the Sicily Sill. Our findings corroborate all those Messinian sea-level reconstructions, forwarding that a single or multiple sea-level stagnancies at the depth of the Sicily Sill lasted long enough to significantly erode the upper slope. Our data also have implications for the ongoing debate of the palaeo-depth of the Sicily Sill. Since the Mallorcan plateau experienced the least vertical movement, the observed terrace depth of 380 m there is inferred to be close to the Messinian depth of this swell.     

Late glacial to Holocene sea-level changes in the Sea of Marmara: new evidence from high-resolution seismics and core studies

The late glacial to Holocene sedimentary record of the northern shelf of the Sea of Marmara (SoM) has been documented by detailed seismo-, chrono-, and biostratigraphic analyses using sub-bottom (Chirp) profiles and sediment cores. During MIS 3 and the main part of MIS 2 (60–15 ¹⁴C ka b.p.), disconnection from the Mediterranean and Black seas together with a dry climate resulted in a regression in the SoM, when the Sea was transformed into a brackish lake. The river incisions below 105 m water depth along the northern shelf took place during the last glacial maximum, when the lake level was modulated by stillstands at −98 and −93 m. The post-glacial freshwater transgressive stage of the Marmara ‘Lake’ occurred between 15 and 13.5 ¹⁴C ka b.p., leading to a rise in water level to −85 m by 13.0 ¹⁴C ka b.p., as evidenced by broad wave-cut terraces along the northern shelf. Since 12 ¹⁴C ka b.p., high-frequency sea-level fluctuations have been identified at the SoM entrance to the Strait of İstanbul (SoI). Thus, wave-cut terraces have been recorded at water depths of −76 and −71 m that, according to an age model for core MD04-2750, have ages of 11.5 and 10.5 ¹⁴C ka b.p., respectively. Ancient shoreline at −65 m along the northern shelf presumably formed soon after the Younger Dryas (YD) at ca. 10.1 ¹⁴C ka b.p. Moreover, there is compelling evidence of Holocene outflow from the Sea of Marmara to the Black Sea. At the SoM entrance to the SoI, the existence of bioherms on the reflector surface together with abundant Brizalina spathulata and Protoglobulimina pupoides in a core suggests a return to higher salinities due to strong Mediterranean water incursion into the SoM at ∼8.8 ¹⁴C ka b.p. This finding is consistent with earlier suggestions that, after the YD, the Black Sea was flooded by outflow from the SoM as a result of global sea-level rise.