Sea level history in Beringia during the past 250,000 years

This paper attempts to relate current knowledge of sea-level history in Beringia to the Broecker-van Donk “Termination” concept of climatic and sea-level history. The Einahnuhtan transgression is thought to represent Termination III, which according to Broecker and van Donk, took place about 225,000 y.a. The Kotzebuan transgression is thought to represent a positive fluctuation that modulated the generally falling sea level during the ensuing 100,000 yr. Sea level probably fell to about ?135 m in the Bering Sea area during the maximum phase of the penultimate glaciation. The two Pelukian shorelines probably represent Termination II (about 125,000 yr BP in the Broecker-van Donk chronology) and one of the two positive fluctuations that modulated the generally falling sea level of early Wisconsinan time, about 105,000 and 80,000 y.a. according to Broecker and van Donk. Another positive modulation brought sea level to at least ?20 m, about 30,000 y.a. Sea level evidently fell to between ?90 and ?100 m during the late Wisconsinan regression, but a substantial part of the outer Bering shelf remained submerged. Submerged shoreline features at ?38m, ?30 m, ?24 to ?20 m, and ?12 to ?10 m represent stillstands or slight regressions that modulated Termination I, the late Wisconsinan, and early Holocene recovery of sea level.     

Landslides along the Jordanian Dead Sea coast triggered by the lake level lowering

The level of the Dead Sea lowers 1 m/year and this rate is in acceleration. The decline is causing one of the major environmental disasters of the twenty-first century. The freshwater resources management policy of Israel, Jordan, and Palestine controls the phenomenon. Since the 1960s, the level of this terminal lake dropped by 28 m and its surface shrunk by one-third. In the 1990s, international builders created major tourist resorts and industrial plants along the Jordanian shore while, during the same period, geological hazards triggered by the level lowering spread out. From the very beginning of the year 2000, sinkholes, subsidence, landslides, and river erosion damaged infrastructures more and more frequently: dikes, bridges, roads, houses, factories, pipes, crops, etc. Until present, scientific articles about this ongoing disaster concerned only sinkholes and subsidence phenomena. This paper focuses on the landslides issue along the Jordanian coast. Based on a set of ground observations collected since 1999, the dynamics of the triggering factors in relation to the evolution of the hydro-geological setting is discussed. It is inferred that the recent industrial and tourist infrastructures never took into consideration the very important geotechnical constraints resulting from the Dead Sea lowering.     

No significant ice-sheet expansion beyond present ice margins during the past 4500 yr at Rauer Group, East Antarctica

The history of glacial advances and retreats of the East Antarctic ice sheet during the Holocene is not well-known, due to limited field evidence in both the marine and terrestrial realm. A 257-cm-long sediment core was recovered from a marine inlet in the Rauer Group, East Antarctica, 1.8 km in front of the present ice-sheet margin. Radiocarbon dating and lithological characteristics reveal that the core comprises a complete marine record since 4500 yr. A significant ice-sheet expansion beyond present ice margins therefore did not occur during this period.     

Human impacts, climate change, and aquatic ecosystem response during the past 2000 yr at Lake Wandakara, Uganda

Analyses of carbon and hydrogen isotope ratios of terrestrial leaf waxes and the carbon and nitrogen abundance, ratio, and isotopic composition of bulk sediments from Lake Wandakara, a crater lake in western Uganda, East Africa, document human and climatic controls on the aquatic system and on the surrounding terrestrial vegetation during the past two millennia. Our data indicate that Wandakara was a relatively stable, productive lake surrounded by C₃ vegetation from AD 70 to 1000. Abrupt changes in the δ¹³C of terrestrial leaf waxes indicate a series of abrupt shifts in the relative abundance of C₃ and C₄ vegetation caused by a combination of climate change and human activities around Wandakara beginning at AD 1000. Abrupt shifts in bulk sediment organic geochemistry, particularly C/N ratios and δ¹⁵N, indicate that human activities at this time caused permanent changes in the limnology of Lake Wandakara, including eutrophication. Our results suggest that the biogeochemistry of Lake Wandakara was more sensitive to shifting human impacts than to climate variations during the past millennium, highlighting the importance of understanding the intensity of pre-colonial human impacts on Africa's aquatic ecosystems.     

A high-resolution diatom-inferred palaeoconductivity and lake level record of the Aral Sea for the last 1600 yr

Formerly the world's fourth largest lake by area, the Aral Sea is presently undergoing extreme desiccation due to large-scale irrigation strategies implemented in the Soviet era. As part of the INTAS-funded CLIMAN project into Holocene climatic variability and the evolution of human settlement in the Aral Sea basin, fossil diatom assemblages contained within a sediment core obtained from the Aral Sea have been applied to a diatom-based inference model of conductivity (r² = 0.767, RMSEP = 0.469 log₁₀ μS cm^− 1). This has provided a high-resolution record of conductivity and lake level change over the last ca. 1600 yr. Three severe episodes of lake level regression are indicated at ca. AD 400, AD 1195–1355 and ca. AD 1780 to the present day. The first two regressions may be linked to the natural diversion of the Amu Darya away from the Aral Sea and the failure of cyclones formed in the Mediterranean to penetrate more continental regions. Human activity, however, and in particular the destruction of irrigation facilities are synchronous with these early regressions and contributed to the severity of the observed low stands.     

Cultivation and human impact at 6000 cal yr B.P. in tropical lowland forest at Niah, Sarawak, Malaysian Borneo

This paper describes palynological evidence for what appears to be comparatively large-scale human impact in the catchment of the Sungai Niah in the wet tropical lowland swamp forests of Sarawak, Malaysian Borneo close to the Great Cave of Niah. Pollen associated with cleared landscapes and rice cultivation is evident in the sedimentary record from before 6000 cal yr B.P. Human activity seems to have been associated with changes in sedimentary regime, with peat-dominated environments being replaced diachronously by clay-dominated deposition. This may reflect anthropogenic soil erosion in the catchment of the Sungai Niah.     

On the character of Black Sea level rise during the Holocene

The character of changes in the mollusk fauna in the Late Pleistocene and Holocene sediments within the Bulgarian, Northwestern, Crimean, and Kerch segments of the Black Sea shelf has been examined. A bed containing fossil remains of brackish-water and marine mollusks was recognized in these sediments; the bed accumulated, based on results of radiocarbon datings, 500–1000 years ago. The obtained data do not support the existing notion of a catastrophic fill-up of the Black Sea Basin by marine Mediterranean water [19].     

Sea level and paleotemperature records from a mid-Holocene reef on the North coast of Java, Indonesia

Mid-Holocene age fossil-fringing reefs occur along the tectonically stable north coast of Java, Indonesia, presenting an opportunity for sea level and paleoclimate reconstruction. The fossil reef at Point Teluk Awur, near Jepara, Central Java, contains two directly superposed horizons of Porites lobata microatolls. Corals in the lower horizon, 80 cm above modern sea level, yielded Uranium series dates of 7090 ± 90 year BP, while corals in the upper horizon at 1.5 m grew at 6960 ± 60 year BP. These dates match the transgressive phase of regional sea-level curves, but suggest a mid-Holocene highstand somewhat older than that recorded on mid-Pacific islands. Paleotemperature was calibrated using Sr/Ca and δ¹⁸O values of a modern P. lobata coral and the locally measured sea surface temperature (SST), yielding SST–Sr/Ca and SST–δ¹⁸O calibration equations [T _Sr/Ca = 91.03–7.35(Sr/Ca) and T_{d¹⁸ \textO} T_{{\delta^{18} {\text{O}}}}  = −3.77 to −5.52(δ¹⁸O)]. The application of the local equations to Sr/Ca and δ¹⁸O measurements on these corals yielded a range of temperatures of 28.8 ± 1.7°C, comparable to that of the modern Java Sea (28.4 ± 0.7°C). A paleo-salinometer [Δδ¹⁸O = ∂δ¹⁸O/∂T ( T_{d¹⁸ \textO} T_{{\delta^{18} {\text{O}}}}  − T _Sr/Ca)], re-calculated using the local parameters, also suggests Java Sea mid-Holocene paleosalinity similar to modern values.     

Paleo-oceanography of the Norwegian Sea during the past 130,000 years: coccolithophorid and foraminferal data

Faunal, floral and sedimentological properties of Norwegian Sea core V27-86 were examined in order to reconstruct the paleo-oceanographic history of this region. Downcore variations in the relative abundance of three microfossil groups and several sediment properties exhibit three different climate response patterns (CRP). Each pattern is judged to represent the response of a different part of the climate system. The covariance patterns among coccoliths, henthic foraminifera, and other properties suggest that the Norwegian Sea has been ice-free and productive during the present interhlacial. the penultimate interglacial (isotopic-stage se) and at least partially ice-free during an intermediate climatic regime (stages sa-d). A maximum change in these measures occurs at the boundary between isotopic stage 5a (an intermediate climatic regime)and isotopic stage 4 (a glacial climatic regime). In contrast, planktic foraminiferal assemblages and oxygen isotope measurements on planktic foraminifera show a major change at the end of stage 5e (the penultimate interglacial). The contrasting behavior of these two sets of observations is explained by a model which postulates a low-salinity surface layer 115,000 to 75,000 years ago (stages 5a-d).     

Evidence of high sea level during the mid- Holocene on the southwest coast of Sri Lanka

A well-developed extensive buried coral reef at Akurala, north of Hikkaduwa, is deposited on a low plateau of decomposed crystalline rocks of Precambrian age. Radiocarbon age datings from three coral quarries in the area reveal that the branching and massive corals, in a position ofgrowth, were gradually deposited between 6, 110 ± 80 B.P. and 5,500 ± 80 B.P. in a bay or a lagoon as isolated patches, and their heights vary from 1.4m to 3.9m below mean sea level (MSL). Four radiocarbon age datings of emerged coral reef patches at Akurala and Akurala- Telwatte vary from 6,170 ± 70 B.P. to 5,350 ± 80 B.P. and at levels between 10cm and 70cm above MSL respectively. The present living corals in front of the southwest coast thrive from mean low water spring (MLWS) tidal level to 4m in depth in lagoonal reef areas. From the level of pesent living coral it is inferred that sea level was above the present level about 50cm at 6,110 ± 80 B.P. and 1m or more at 5,560 ± 80 B.P. The in situ position and condition of the materials show that they were not accumulated by catastrophic events such as storm waves.     

Human-induced geological hazards along the Dead Sea coast

The Dead Sea is a terminal lake whose level is currently dropping at a rate of about 1 m per year due to the over exploitation of all its tributaries. The lowering started about four decades ago but geological hazards appeared more and more frequently from the end of the 1980s. The water level lowering is matched by a parallel groundwater level drop, which results in an increasing intensity of underground and surface water flow. The diagonal interface between the Dead Sea brine and the fresh groundwater is pushed downwards and seawards. Nowadays, sinkholes, subsidence, landslides and reactivated salt-karsts affect wide coastal segments. Until now, mainly infrastructures were damaged and few people/animals were injured, but the ongoing development of tourism in this very attractive situation will increase the risk if precautionary measures are not included in the development plans. This paper discusses the main observations made all around the Dead Sea and shed a light on the differences between the geological hazards of the western shore (Israel, Palestinian Authority) and the eastern shore (Jordan). It is the first attempt to bring together an overview of the human-induced geological hazards encountered along the Dead Sea coast.     

Variation of paleo-productivity and terrigenous input in the Eastern Arabian Sea during the past 100 ka

A 4.1 m long sediment core from the Eastern Arabian Sea (EAS) is studied using multiple geochemical proxies to understand the variation of productivity and terrigenous matter supply during the past 100 ka. The temporal variation in element concentration and fluxes of CaCO₃, organic carbon (C_org) and Barium excess (Ba_exc), together, in general indicate a higher productivity during the cold climate and highest during the Last Glacial Maximum (LGM) in particular. This cold climate-increased productivity coupling may be attributed to the shoaling of nutricline due to enhanced convective mixing resulting from the intensified winter monsoon. Increased linear sedimentation rates and fluxes of Al, Fe, Mg, Ti, Cr, Cu, Zn, and V during the cold period also suggest increased input of terrigenous matter supporting intensified winter winds. However, the presence of large abundance of structurally unsupported elemental content (e.g.: Mg-86%, Fe-82% and Al-53%) indicate increased input of terrigenous material which was probably enhanced due to intense winter monsoon.     

Climate on the southern Black Sea coast during the Holocene: implications from the Sofular Cave record

We present the updated Holocene section of the Sofular Cave record from the southern Black Sea coast (northern Turkey); an area with considerably different present-day climate compared to that of the neighboring Eastern Mediterranean region. Stalagmite δ¹³C, growth rates and initial (²³⁴U/²³⁸U) ratios provide information about hydrological changes above the cave; and prove to be more useful than δ¹⁸O for deciphering Holocene climatic variations. Between ～9.6 and 5.4 ka BP (despite a pause from ～8.4 to 7.8 ka BP), the Sofular record indicates a remarkable increase in rainfall amount and intensity, in line with other paleoclimate studies in the Eastern Mediterranean. During that period, enhanced summertime insolation either produced much stronger storms in the following fall and winter through high sea surface temperatures, or it invoked a regional summer monsoon circulation and rainfall. We suggest that one or both of these climatic mechanisms led to a coupling of the Black Sea and the Mediterranean rainfall regimes at that time, which can explain the observed proxy signals. However, there are discrepancies among the Eastern Mediterranean records in terms of the timing of this wet period; implying that changes were probably not always occurring through the same mechanism. Nevertheless, the Sofular Cave record does provide hints and bring about new questions about the connection between regional and large scale climates, highlighting the need for a more extensive network of high quality paleoclimate records to better understand Holocene climate.     

库水位升降作用下大型堆积体边坡变形破坏预测

库岸边坡的变形破坏及稳定性研究是目前国内外研究的热点之一。基于水电站库区一大型堆积体边坡,通过现场原位直剪试验获取岩土体的力学参数,利用岩土数值分析FLAC3D软件,考虑了堆积体与基岩基覆接触带介质的应变软化特性,对水库蓄水和下降过程中边坡的变形破坏特征进行了分析预测。结果表明,在库水升降作用下变形主要发生在堆积体内部;根据堆积体的变形特征可分为3个区：前缘牵引变形区,变形量最大;中间过渡区,变形量最小;后缘被牵引变形区,变形量介于前缘和中间之间。模拟过程中,在坡体的不同位置设置位移监测点,得到了蓄水和水位下降过程中各监测点的位移时程曲线,监测结果显示,水位下降时堆积体前缘易形成局部失稳。通过剪应变增量判断堆积体边坡在库水作用下可形成2个潜在的滑动破坏面     

Vegetation response to rapid climate change in central europe during the past 140,000 yr based on evidence from the Füramoos pollen record

The response of Central European vegetation to rapid climate change during the late Quaternary period (Eemian to Holocene) is assessed by data from the new pollen record of Füramoos, southwestern Germany. This record represents the longest late Quaternary pollen record north of the Alps as currently known. Its high degree of completeness allows detailed correlations with Greenland ice cores and sea-surface temperature records from the North Atlantic. Our data show that if climate deteriorations were not long or severe enough to extirpate refugia of arboreal taxa north of the Alps such as during marine oxygen isotope stage (MIS) 5 (i.e., Würm Stadial A, Stadial B, and Stadial C), reforestation with the onset of warmer conditions in Central Europe occurred on a centennial scale. If arboreal taxa became completely extinct north of the Alps such as during MIS 4 (i.e., Würm Stadial D), several thousand years were necessary for the reimmigration from refugia situated in regions south of the Alps. Thus, Dansgaard-Oeschger interstades (DOIS) 24 to 20 and 15 to 11 are expressed in Central European pollen records, whereas DOIS 19 to 16 are not recorded due to migration lags.     

库水位波动条件下万州瓦窑坪滑坡稳定性分析

库水位波动对滑坡的稳定性变化有重要影响,传统的定值分析方法未能考虑土体强度参数取值的不定性,而概率分析法能考虑土体强度参数分布的随机性,对库区滑坡的稳定性分析提供了更有力的依据。文章以万州瓦窑坪滑坡为例,在基于库水位实际波动进行拟合的条件下对滑坡的渗流场进行了模拟,同时对不同水位下滑坡的稳定性和破坏概率进行了分析。结果表明,滑坡在库水位波动条件下整体稳定性系数均大于1,处于基本稳定状态,滑坡具有低危险性。库水位下降到160.47 m水位时,边坡破坏概率超过30%,具有中等危险性。采用R/S分析法对监测数据进行分析,结果表明滑坡具有持续性的小变形,滑坡处于基本稳定状态,与稳定性分析结果一致。     

Geomorphic and climatic change over the past 12,900 yr at Swiftcurrent Lake, Glacier National Park, Montana, USA

Glaciated alpine landscapes are sensitive to changes in climate. Shifts in temperature and precipitation can cause significant changes to glacier size and terminus position, the production and delivery of organic mass, and in the hydrologic energy related to the transport of water and sediment through proglacial environments. A sediment core representing a 12,900-yr record collected from Swiftcurrent Lake, located on the eastern side of Glacier National Park, Montana, was analyzed to assess variability in Holocene and latest Pleistocene environment. The spectral signature of total organic carbon content (%TOC) since ~ 7.6 ka matches that of solar forcing over 70-500 yr timescales. Periodic inputs of dolomite to the lake reflect an increased footprint of Grinnell Glacier, and occur during periods when sediment sinks are reduced, glacial erosion is increased, and hydrologic energy is increased. Grain size, carbon/nitrogen (C/N) ratios, and %TOC broadly define the termination of the Younger Dryas chronozone at Swiftcurrent Lake, as well as major Holocene climate transitions. Variability in core parameters is linked to other records of temperature and aridity in the northern Rocky Mountains over the late Pleistocene and Holocene.