Late Quaternary climate-driven environmental change in the Larsemann Hills, East Antarctica, multi-proxy evidence from a lake sediment core

Little is known about the response of terrestrial East Antarctica to climate changes during the last glacial-interglacial cycle. Here we present a continuous sediment record from a lake in the Larsemann Hills, situated on a peninsula believed to have been ice-free for at least 40,000 yr. A mutli-proxy data set including geochronology, diatoms, pigments and carbonate stable isotopes indicates warmer and wetter conditions than present in the early part of the record. We interpret this as Marine Isotope Stage 5e after application of a chronological age-depth model and similar ice core evidence. Dry and cold conditions are inferred during the last glacial, with lake-level minima, floristic changes towards a shallow water algal community, and a greater biological receipt of ultraviolet radiation. During the Last Glacial Maximum and Termination I the lake was perennially ice-covered, with minimal snowmelt in the catchment. After ca. 10,500 cal yr B.P., the lake became seasonally moated or ice-free during summer. Despite a low accumulation rate, the sediments document some Holocene environmental changes including neoglacial cooling after ca. 2450 cal yr B.P., and a gradual increase in aridity and salinity to the present.     

Quaternary sedimentation of the Alaskan Beaufort shelf: Influence of regional tectonics, fluctuating sea levels, and glacial sediment sources

The offshore stratigraphy of the Quaternary Gubik Formation of Arctic Alaska has been studied on high-resolution seismic profiles with a maximum sub-seafloor penetration of about 100 m. In general, marine transgressive subunits of the Gubik Formation are wedge-shaped on the shelf, thickening slightly seaward to the shelf break, beyond which they are offset by landslides and slumps. Beneath the eastern third of the Alaskan Beaufort shelf, active folding has created two persistent structural depressions, the Eastern and Western Wedge Terranes, in which the wedge morphology is especially well developed. The youngest transgressive marine wedge, which was deposited in such a way as to fill these depressions, leaving a generally flat present-day shelf surface, is inferred to be late Wisconsin or younger in age because it overlies a prominent disconformity interpreted to have been formed during the late Wisconsin glacial sea-level minimum. The thickness of this youngest wedge, Unit A, locally exceeds 40 m on the outer shelf, yet apparently relict gravel deposits collected from its seabed surface indicate that the depositional rate is presently quite low on the middle and outer shelf. Lithologies of the gravels are exotic to Alaska, but similar to suites exposed in the Canadian Arctic Islands. These observations suggest a depositional scenario in which the retreating Laurentide Ice Sheet shed sediment-laden icebergs from the Canadian Arctic Islands into the Arctic Ocean following the late Wisconsin glacial maximum. These bergs were then rafted westward by the Beaufort Gyre and grounded on the Alaskan shelf by northeasterly prevailing winds. Especially large numbers of bergs accumulated in the wedge terrane embayments—created as sea level rose—and melted there, filling the embayments with their sedimentary cargo. As glacial retreat slowed, depositional rates on the shelf dwindled.This mode of deposition in the Alaskan Beaufort wedge terranes may be typical of early post-glacial transgressive phases throughout Quaternary time. It has resulted in the preservation of disconformities that apparently formed during glacioeustatic lowstands, and whose seaward termination depths, appropriately corrected, may yield estimates of lowstand magnitudes. Knowledge of global sea-level fluctuations back through the Sangamon Interglacial (oxygen isotope stage 5e) and possible correlations with dated onshore deposits have facilitated a tentative correlation of major disconformities in the Beaufort Sea record with major ¹⁸O enrichment maxima in the oxygen isotope curve back through stage 8. In this tentative scheme, close similarities between the two data sets occur both in magnitudes and in numbers of fluctuations intervening between major correlation points. Further testing of the Quaternary depositional model suggested here and of the resulting sea level curve awaits the collection and dating of core samples from the Beaufort wedge terranes.     

Isotopic evidence of lead sources in Loire River sediment

Sediments along the Loire River (central France) were investigated by means of Pb isotopes determined on the labile sediment fraction, or acid-extractable matter (AEM). The combination of trace elements and Pb isotopes allows deciphering the origin of the elements (i.e. natural or anthropogenic) and their history, in the sediment from two small watersheds (one draining basalt, the other one granite–gneiss), both in present-day suspended matter in Loire River water, and in sediment from the Loire estuary. Crustal weathering, as confirmed by the Pb-isotope ratios for most sample points, is the main source of Pb in the upstream part of the Loire River, as well as that transported in the middle part of the basin and in the estuary. Among anthropogenic sources, the use of Pb-isotopic compositions shows an influence of agriculturally-derived Pb inputs and a major input of Pb derived from gasoline, particularly in the estuary due to harbor activities.     

Holocene climate variability from lake sediment core in Larsemann Hills,Antarctica

A sediment core (L2) from Larsemann Hills, Antarctica was analyzed for Biogenic Silica (BSi), Sand (%) and Total Organic Carbon (TOC). The 78 cm core length represents the time span of ∼8.3 cal ka BP. The values of BSi from the core show prominent high productivity from ∼8.3 to ∼6 cal ka BP in comparison to less productivity in mid-late Holocene (∼6 cal ka BP to recent). Moreover, high sand (%) infers the glacio-fluvial deposition from ∼8.3 to ∼5 cal ka BP TOC shows little variation through out the core, except in the upper ∼10 cm (∼4 cal ka BP) part wherein it is comparatively high. The increased TOC in the upper part of the core possibly indicates presence of algal mat due to exposure of the lake to the ice free (glacier free) conditions.     

Mapping sediment sources in a New Zealand Mountain Watershed

Planning of soil conservation and erosion control schemes to minimize downstream effects requires information on the sources of sediment supply to a river system. A survey technique for providing an inventory of sediment sources has been developed in New Zealand; sediment sources are classified in terms of geomorphic type and degree of activity (severity). The technique is qualitative but is of value for both planning and research because it demands a formal, objective examination of the area under study. In the Harper-Avoca watershed the technique demonstrated that some well-established beliefs regarding the supply of sediment to the river systems might be erroneous; sediment supply appears to be controlled primarily by geomorphic and geologic factors, and human interference with the ecosystem probably has had a minor effect on rates of supply. The bulk of the sediment comes from large, natural features that are beyond present erosion-control technology, whereas those features that could be effectively treated supply a relatively small proportion of the river's total sediment load.     

The Late Quaternary sediment successions of Llangorse Lake,south Wales

The last British-Irish Ice Sheet (BIIS) created a landscape with many sedimentary basins that preserve archives of paleoenvironmental and paleoclimatic change during the Last Glacial-Interglacial Transition (LGIT; ~ 18-8 ka BP). The typical lithostratigraphic succession of these archives is composed of minerogenic/allogenic sediments formed during cold climatic conditions and organic-rich/authigenic sediments during warmer climates. This paper presents a multi-core lithostratigraphy compiled from the extant lake and surrounding basin at Llangorse Lake, south Wales, a basin lying within the southernmost limits of the last BIIS. This lake contains one of the longest continuous terrestrial sediment successions in the UK. Uncertainty previously existed concerning the presence and distribution of sediments at the site related to the Windermere Interstadial (~ 14.7 to ~ 12.9 ka BP) and Loch Lomond Stadial (~ 12.9 to 11.7 ka BP). A new borehole survey demonstrates that LGIT-age sediments are present at the site with nekron mud (gyttja), corresponding to the Lateglacial Interstadial, deposited in the deeper part of the lake waters and that these deposits are equivalent in age to marl deposits found at shallower depths at the margins of the basin. These deposits are associated with warmer conditions experienced during the Windermere Interstadial and Holocene, whilst minerogenic-rich sediments were deposited during the colder climatic conditions of the Dimlington Stadial and the Loch Lomond Stadial with rangefinder radiocarbon dates confirming this attribution. A model of lake level changes shows that drainage of the Dimlington Stadial glacial lake caused the largest fall, but there was also a further, smaller lake level fall at the end of the Windermere Interstadial and/or the start of the Loch Lomond Stadial, before the level rose in the early Holocene. The lithostratigraphic results presented here form the framework for further paleoenvironmental and paleoclimatic research at Llangorse Lake.     

Late Quaternary deglaciation and climate history of the Larsemann Hills (East Antarctica)

The Late Quaternary climate history of the Larsemann Hills has been reconstructed using siliceous microfossils (diatoms, chrysophytes and silicoflagellates) in sediment cores extracted from three isolation lakes. Results show that the western peninsula, Stornes, and offshore islands were ice‐covered between 30 000 yr BP and 13 500 cal. yr BP. From 13 500 cal. yr BP (shortly after the Antarctic Cold Reversal) the coastal lakes of the Larsemann Hills were deglaciated and biogenic sedimentation commenced. Between 13 500 and 11 500 cal. yr BP conditions were warmer and wetter than during the preceding glacial period, but still colder than today. From 11 500 to 9500 cal. yr BP there is evidence for wet and warm conditions, which probably is related to the early Holocene climate optimum, recorded in Antarctic ice cores. Between 9500 and 7400 cal. yr BP dry and cold conditions are inferred from high lake‐water salinities, and low water levels and an extended duration of nearshore sea‐ice. A second climate optimum occurred between 7400 and 5230 cal. yr BP when stratified, open water conditions during spring and summer characterised the marine coast of Prydz Bay. From 5230 until 2750 cal. yr BP sea‐ice duration in Prydz Bay increased, with conditions similar to the present day. A short return to stratified, open water conditions and a reduction in nearshore winter sea‐ice extent is evident between 2750 and 2200 cal. yr BP. Simultaneously, reconstructions of lake water depth and salinity suggests relatively humid and warm conditions on land between 3000 and 2000 cal. yr BP, which corresponds to a Holocene Hypsithermal reported elsewhere in Antarctica. Finally, dry conditions are recorded around 2000, between 760 and 690, and between 280 and 140 cal. yr BP. These data are consistent with ice‐core records from Antarctica and support the hypothesis that lacustrine and marine sediments on land can be used to evaluate the effect of long‐term climate change on the terrestrial environment. Copyright © 2004 John Wiley & Sons, Ltd.     

Transition in Late Quaternary Paleoclimate in Schirmacher Region,East Antarctica as Revealed from Lake Sediments

The lacustrine sediments are one of the best sources to provide information on climate change, specially in peri-glacial climatic region. Schirmacher Oasis, located on the Princess Astrid Coast in Queen Maud Land, is one of the few areas in East Antarctica that provides valuable information on paleoclimate of the region with various depositional features formed due to deglaciation process. This Oasis is dotted with more than 100 lakes of proglacial, land-locked and epi-shelf type. The multi-proxy sedimentological data, generated from the sediment cores from land-locked lakes and grab sample from a proglacial lake, lying in the same drainage line in the central part of Schirmacher region has provided better insight into the paleoclimatic evolution of the region. The immature and chemically unaltered lake sediments have shown restricted drainage pattern. Different phases of warmer and cooler intervals are highlighted by the patterns of fluctuations in different sedimentological and statistical parameters. The dominance of glacial signatures is very clear on the lake sediments as revealed by the surface textures of quartz grains. Physical weathering has mainly controlled the overall sediments and the composition of clay fraction. The clay minerals indicate a gradual shift in the weathering regime and therewith in climate from strongly glacial to fluvioglacial specially around 42 ka. This indicates beginning of warming of the area much before the LGM. But the warm period is not strong enough to alter the overall clay chemistry. Proxy records indicate short-period climatic oscillations during late Quaternary.     

Dinoflagellate cysts in Upper Quaternary sediments from southwestern Norway and potential correlations with the oceanic record

Twenty-two samples from two locations at the Foss-Eigeland clay and gravel pit, Jæren, southwestern Norway were analysed for dinoflagellate cysts. Cyst recovery was generally poor and cyst assemblages indicate a cold temperate to arctic glacimarine environment. The percentage composition of a total of 19 cyst species identified allowed the recognition of five assemblage zones. These are thought to reflect fluctuating minor climatic changes during an interstadial period preceding the last glacial advance in the region. Cyst assemblages from these supposedly Middle Weichselian sediments at Foss-Eigeland are similar to those found in the northern North Sea and the Norwegian Sea in probably similarly aged sediments. This suggests a potential for using dinoflagellate cysts to correlate land-based Quaternary sequences with the deep sea record.     

Late Quaternary sediment, sediment mass flow processes and slope stability on the Scotian Slope, Canada

The study area, just to the west of the Verrill Canyon on the Scotian Slope, eastern Canada, exhibits both large and small scale sediment mass movement features. Study of high resolution seismic reflection and sidescan sonar data shows that a large portion (approximately 70%) of the near surface sediment (<20 m) in the area has undergone erosion, rotational slumping and internal deformation. Remoulded sediment observed in physical properties profiles of piston cores and sediment deformation structures are further evidence of slumping. Small scale mass flow events are recorded by abundant turbidites and debris flow deposits noted in piston cores. Sediment physical properties are highly dependent on sediment type (lithofacies). Frequent facies changes, both temporally and spatially, make correlation between cores difficult. Although the small scale mass movement events correlate with glacial recession on the continental shelf and lower relative sea levels, the triggering mechanisms for the large scale events are less obvious. Slope stability analyses indicate that, at present, the seabed is stable. The most plausible explanation for large scale slope failures in this region are ground accelerations related to earthquake shock. Our analyses demonstrate that it is unlikely that large magnitude, distant earthquakes, such as those previously proposed in the Laurentian Slope Seismic Zone (LSP) model, could initiate failure of sediment in the study region. Our data support the interpretation that more frequent, lower magnitude earthquakes, closer to the study region, as previously proposed in the Eastern Slope Experimental Source Zone (ESX) model, are the likely causes of large scale slope failures. Furthermore, excess pore pressures resulting from shallow gas and/or high sedimentation rates during deglaciation contribute to slope failure.     

Evolution of the Kerguelen plume and its impact upon the continental and oceanic magmatism of East Antarctica

Petrological–geochemical study showed that the alkaline-ultramafics of the Jetty Oasis (rift zone of the Lambert glacier, East Antarctica) are similar in the age (117–110 Ma) and geochemistry to the ultrapotassic alkali basalts of eastern India (Jharia and Raniganj intrusions). Alkaline magmatism in India and Antarctica is related to the activity of the Kerguelen plume, which significantly affected the evolution of the entire eastern Indian Ocean, in particular, determined geodynamic peculiarities of the ocean opening (existence of non-spreading blocks, fragments of the Gondwana lithosphere in oceanic areas) and geochemical characteristics of erupted tholeiitic magmas. Enriched magma sources related to the Kerguelen plume were formed by melting of ancient Gondwana-derived continental fragments, which experienced multiple transformations during its evolution up to the formation of metasomatized mantle under the impact of the Kerguelen plume on the Antarctic and India margins.     

Palaeoseismic (?) liquefaction event in late Quaternary lake sediment at Glen Roy,Scotland

Late Quaternary lake sediment deposits from a former ice-dammed lake at Glen Roy, Scotland, contain deformation structures indicative of liquefaction. The distribution of deformation styles reflects a concentric pattern of the degree of liquefaction. A possible fault rupture and several landslides are also observed in the central area. The liquefaction structures, the zonation of the sediment deformation and the association of deformation with landsliding can most simply be interpreted in terms of ground shaking during a major earthquake occurring at the end of the last glacial episode in Scotland (c. 10,000 bp).     

Tephrochronology of the Siple Dome ice core,West Antarctica: correlations and sources

A total of 24 tephra-bearing volcanic layers have been recognized between 550 and 987 m depth in the Siple Dome A (SDM-A) ice core, in addition to a number already recognized tephra in the upper 550 m (Dunbar et al., 2003, Kurbatov et al., 2006). The uniform composition and distinctive morphological of the particles composing these tephra layers suggest deposition as a result of explosive volcanic eruptions and that the layers therefore represent time-stratigraphic markers in the ice core. Despite the very fine grain size of these tephra (mostly less than 20 microns), robust geochemical compositions were determined by electron microprobe analysis. The source volcanoes for these tephra layers are largely found within the Antarctic plate. Statistical geochemical correlations tie nine of the tephra layers to known eruptions from Mt. Berlin, a West Antarctic volcano that has been very active for the past 100,000 years. Previous correlations were made to an eruption of Mt. Takahe, another West Antarctic volcano, and one to Mt. Hudson, located in South America (Kurbatov et al., 2006). The lowest tephra layer in the ice core, located at 986.21 m depth, is correlated to a source eruption with an age of 118.1 ± 1.3 ka, suggesting a chronological pinning point for the lower ice. An episode of anomalously high volcanic activity in the ice in the SDM-A core between 18 and 35 ka (Gow and Meese, 2007) appears to be related to eruptive activity of Mt. Berlin volcano. At least some of the tephra layers found in the SDM-A core appear to be the result of very explosive eruptions that spread ash across large parts of West Antarctica, off the West Antarctic coast, as well as also being recognized in East Antarctica (Basile et al., 2001, Narcisi et al., 2005, Narcisi et al., 2006). Some of these layers would be expected to should be found in other deep Antarctic ice cores, particularly ones drilled in West Antarctica, providing correlative markers between different cores. The analysis of the tephra layers in the Siple Dome core, along with other Antarctic cores, provides a timing framework for the relatively proximal Antarctic and South American volcanic eruptive events, allowing these to be distinguished from the tropical eruptions that may play a greater role in climate forcing.     

南海晚新生代地层结构特征、沉积厚度及沉积模式

本文综合地震、钻井及区域地质资料，通过分析地震相参数等，研究南海晚新生代（E3-Q）地层结构特征和沉积厚度变化，建立了晚新生代沉积模式，所取得的研究成果可为南海油气的进一步勘探开发提供有效的基础资料。     

不同碳源对砷污染沉积物中砷的微生物降解的影响

在试验室通过使用多种碳源（包括醋酸盐、乳酸盐和葡萄糖），对采于朝鲜废弃金银矿地区的受砷污染的沉积物样品（339毫克／千克）中固有细菌生物激化后，就沉积物样品中固有细菌对砷物种形成和活动性的影响，进行了研究。通过连续提取分析来确定砷的形式，结果表明，沉积物中40％和47％的砷分别以铁伴生物和残留组分的形式存在。通过使用醋酸盐和乳酸盐对沉积物样品进行培育22天后，固有细菌增加了沉积物样品中铁伴生物和残留组分中溶解砷的总量。当与消过毒的沉积物样品（总溶解砷浓度低于50％）对比时发现，生物悬浮液中超过99％的溶解砷以砷（V）的形式存在，这表明，固有细菌将部分溶解的砷（III）转换成了砷（V）。在实际环境中，依据pH值的不同，微生物引起的水成砷（V）既可以通过吸附而固定不动，也可以在向地下缺氧区迁移后被还原成（III）。     

Multiple Quaternary erosion and infill cycles in overdeepened basins of the northern Alpine foreland

The cumulative effect of repeated extensive glaciations represents a poorly constrained component in the understanding of landscape evolution in mid-latitude mountain ranges such as the Alps. Timing, extent, and paleo-climatic conditions of these glaciations are generally poorly understood due to the often-fragmentary character of terrestrial Quaternary records. In this context, the sedimentary infills of subglacial basins may serve as important archives to complement the Quaternary stratigraphy over several glacial–interglacial cycles. In this study, sedimentary facies, valley-fill architecture, and luminescence dating are used to describe nine erosional and depositional cycles (Formations A–I) in the Lower Glatt valley, northern Switzerland. These cycles can be related to the ‘Birrfeld’ Glaciation (~ MIS2), the ‘Beringen’ Glaciation (~ MIS6), and up to three earlier Middle Pleistocene glaciations that can be tentatively correlated to the regional glaciation history. Evidence suggests that deep bedrock trough incision and/or partial re-excavation last occurred mainly during the ‘Beringen’ and ‘Habsburg’ Glaciations. Second-order, ‘inlaid’ glacial basins document separate glacier re-advances during the Beringen Glaciation. The arrangement of subglacial basins in the Glatt valley with different sub-parallel or bifurcating bedrock troughs, re-excavated segments, and inlaid basins document changes in the magnitude and the spatial focus of subglacial erosion over time. The Glatt valley may thus serve as a key example for the glacial landscape evolution in many other repeatedly glaciated forelands.     

地震方法在城市浅覆盖区活断层调查中的应用

反射地震方法是当前探测城市地震活断层的主要方法,该方法在厚覆盖区探测效果较好.在浅覆盖区采用的接收排列长度较短,震源干扰波对浅层反射波干扰严重,且要求的分别率较高,应用反射地震方法探测城市活断层难度较大.北戴河鸽子窝断裂是秦皇岛—大连断裂在陆地上的一部分.由于该断裂为隐伏断裂,对断裂的倾向、断距、上断点和空间展布存在不确定性.为查明该断裂的空间展布形态、性质以及活动性,采用高精度浅层地震探测技术探测该断裂获得了十分清晰的反射地震图像,依据该地震剖面能够对第四系内部界面、基岩和基岩风化层及断裂构造进行解释,为钻孔联合剖面位置的布设、钻孔深度的设计以及断裂活动性的评价提供了依据.最后经高精度钻孔联合地质剖面证实,地震勘探方法反演得到的主要地层界面和断裂构造特征与钻孔联合地质剖面吻合较好.     

祁连山七一冰川区表层沉积物中生物标志化合物的组成特征及来源研究

利用GC和GC—MS的分析方法,对祁连山七一冰川冰雪不溶微粒、冰尘和七一冰川流域表层土壤中的烷烃、脂肪酸、脂肪酸甲酯和长链酯、酮以及多环芳烃等生物标志化合物进行了分析,研究了它们的组成和分布特征,讨论了它们的环境地球化学意义。结果表明,生物标志化合物分布特征组成和分布特征指示了七一冰川地区的有机质具有藻类、高等植物、化石燃料燃烧产物等多种来源。冰雪不溶微粒和七一冰川流域表层土壤中有机物的来源相似,且这两种介质中的有机污染物种类多于冰尘,表明快速的工业化已经对七一冰川及其周围环境产生明显影响。     

利用两种指纹因子判别小流域泥沙来源

为精确识别黄土高原丘陵沟壑区典型小流域泥沙来源,分析了流域内“源-汇”地区土壤的理化性质及生物标志物（正构烷烃）作为潜在指纹识别因子,并建立了复合指纹模型。结果显示:单独的土壤理化指纹及正构烷烃均不能有效识别泥沙来源;土壤理化指纹和正构烷烃分别在林地、农地及沟道的辨别上显示出其局限性。多元化的复合指纹（碳优势指数CPI、Ca、TP、C₂₀、C₂₉、Fe）则能辨别90.5%的泥沙来源。模型结果显示沟道是该流域泥沙的主要来源,占60.8%,其次为农地占20.7%,林地占11.3%,草地占7.2%。研究表明,结合生物标志物的复合指纹法能更精确地反映泥沙来源,适用于各泥沙源头的地质条件差异较小的流域,对黄土高原小流域水土流失治理具有指导意义。