Multi-proxy evidence for Holocene lake-level and salinity changes at An Loch Mór,a coastal lake on the Aran Islands,Western Ireland

Curves for Holocene lake levels and salinity changes are presented for An Loch Mór, a small oligohaline lake on the Aran Islands off the west coast of Ireland, based on palaeoecological investigations of a 12 m long, lake-sediment core. New insights are also provided into Holocene sea-level change in the Galway Bay region. Particular emphasis has been placed on the ostracod fauna, both past and present. Salinity and lake-level changes were reconstructed from the fossil ostracod assemblages, based on the known tolerances of individual species and on the assemblages as a whole. Additional evidence was provided by other proxies including strontium–isotope ratios derived from ostracod shells and other carbonates, plant macrofossil and pollen analyses, and sedimentological changes. The early Holocene (pre-Boreal, i.e. 11.5–10 ka) was characterised by low lake levels and slightly elevated salinity values, probably the result of high evapotranspiration and low precipitation rather than elevated sea levels. Early Holocene plant and animal migration to the island does not seem to have been impeded but relative sea levels were not necessarily so low (below −40 m a.s.l.) that landbridges were present to the mainland. Between ca 10 and 8.5 ka, relatively high lake levels prevailed. At 8.3 and 7.5 ka, minor fluctuations (lowering) of the lake level occurred that are assumed to relate to early Holocene abrupt events. Beginning at 7.05 ka, lake levels declined sharply. A general trend towards rising lake levels started at ca 6.4 ka and accelerated at ca 5.6 ka as runoff increased as a result of Neolithic clearances. At ca 4.8 ka, lake levels began to rise once again, probably in response to changes in rainfall and/or evapotranspiration and runoff. Lower lake levels during the first half of the 1st millennium AD were probably a response to decreased runoff as a result of a drier climate coupled with regeneration of woody vegetation. The sharpest rise in both lake levels and salinity began during the ninth century AD, which is attributed to a rapid rise in relative sea level.     

Multi-proxy evidence for Late Pleistocene-Holocene climatic and environmental changes in Lop-Nur,Xinjiang, Northwest China

A 10.35-m-long sediment core from the Luobei depression in Lop-Nut, Xinjiang, Northwest China, pro- vides detailed information about environmental changes during the Late Pleistocene. The samples taken every 5 cm of the core were analyzed for 10 environmental proxies, including magnetic susceptibility, granularity, chroma, car-bonate and loss on ignition （LOI）, and pH value. The chronology data are provided by the uranium/thorium disequi-librium dates. The sediments of the section were deposited during the last 32000 years. The results of analysis of 10 proxies were examined using multivariate statistical analysis, and the principal components were calculated. According to the results, the Late Pleistocene sequence contains four climatic and environmental stages appearing in the cycles of cold-wet and warm-dry changes. During 10-9 ka BP, it was the earliest warm episode in the Holocene. Environmental changes in this district were restricted by global change, as suggested by the analysis of glacial-interglacial cycles. But it was different from the mutative trend of a monsoon region in East China because of its own characteristics, which was the situation of cold-wet and warm-dry climate-environment change. The candidate reason may be the uplift of the Tibet Plateau and the westerly wind circulation.     

Evaluation of the Holocene environmental changes of the southwest coast, India: A palaeopalynological approach

The climatic variability and the influence of temperature and sea level fluctuations on the earth??s surface configuration during the Holocene are being discussed all over the world. The present study evaluates the palaeo-environmental conditions of western coast of India during this epoch through the analysis of pollen grains embedded in a carbonaceous clay formation (? 0.4?C0.6?m) found sandwiched within the palaeodeposit of sand of Meenachil River basin. The carbon dating revealed that the clay formation has an age of 5786 ± 94 ¹⁴C yr BP, while the embedded wood samples have the age varying in between 2888 ± 78 and 5780 ± 95 ¹⁴C yr BP. The overall analysis suggests that the southwestern margin of India had experienced high intensity rainfall during the earlier part of the Atlantic chronozone due to then strengthened Asiatic monsoon, while water stagnation and hydrological modifications were observed during the later part. The dominance of weeds and lesser number of tree elements suggested a drier climate during the end of the Atlantic period. Besides, the morphometric rearrangement of the Meenachil River contemporaneous to the geomorphological modifications of the southwestern coast of India shall be classified into three categories: (1) Pre-Vembanad Lake formation, (2) Contemporaneous to lake formation and (3) Post-Lake formation.     

Tepexpan Palaeoindian site, Basin of Mexico: multi-proxy evidence for environmental change during the late Pleistocene–late Holocene

The Tepexpan Palaeoindian skeleton was discovered in 1947 close to the former Lake Texcoco margin, in the Basin of Mexico. The find has been the object of considerable interest and discussion over the last 60 years regarding its real age and archaeological interpretation. Here we report new AMS radiocarbon dates associated with the sedimentary succession at Tepexpan with ages between 19,110 ± 90 and 612 ± 22 ¹⁴C years BP and a new uranium-series date for the skeleton with an age of 4700 ± 200 years BP that indicates a mid Holocene age. The sedimentary succession was studied in detail using: stable isotopes, diatoms, organic geochemistry and tephrochronology. The multi-proxy evidence suggests large changes around the margins of Lake Texcoco in terms of the balance between aquatic and terrestrial plants, C₃ and C₄ plants, saline, alkaline and freshwater conditions, volcanic activity, marginal reworking of lake sediments and input from the drainage basin through the late Pleistocene–late Holocene. These changes had large impacts on the prehistoric human populations living by the lake shores since the late Pleistocene in the Basin of Mexico.     

Late Holocene environmental changes and anthropogenic impact in Dee Why Lagoon,New South Wales

Late Holocene environmental changes were examined in Dee Why Lagoon, New South Wales, based on the sedimentological, geochemical and geochronological analysis of six cores collected from the fluvial delta and lagoon basin. The lagoon formed about 7300–7200?cal yr BP, following the post-glacial marine transgression and establishment of a sand barrier. Infilling of the lagoon occurred at a rate of 0.09–0.15?mm/yr until about 3300–3200?cal yr BP, when the barrier closed, resulting in mostly freshwater conditions, as evidenced by a change from pyrite-rich units to sediment containing little sulfur and a lack of foraminifera. Sedimentation rates increased to 0.23 then 0.43?mm/yr until about 100?years ago. Post-European land clearance led to an increase in sedimentation rates to 1.0–1.3?mm/yr on the fluvial delta, which are lower than those from other wave-dominated estuaries in New South Wales as well as those estimated by previous studies in Dee Why Lagoon. Our study shows that the fluvial delta started forming much earlier than originally thought, based on results of radiometric dating, and confirmed using sedimentological and geochemical data, as well as a critical examination of historic aerial photographs. Human impact has resulted in an increase in heavy metal (Cu, Pb, Zn) and metalloid (As) concentrations in the recent sediment, most likely attributed to stormwater discharge. Pb and As concentrations are above the ANZECC high sediment quality guideline values at the site closest to the stormwater outlet, with As-based pesticides one of the possible sources. Using the mean enrichment quotient, which is based on normalised Cu, Pb and Zn concentrations over their normalised background concentrations, we show that the surface sediments in Dee Why Lagoon are severely enriched, reflecting the recent anthropogenic impact that has also led to an increase in sedimentation rates.     

Propagation characteristics of historical tsunamis that attacked the east coast of Korea

In this study, a numerical modeling system based on the dispersion–correction finite difference scheme equipped with a grid-nesting scheme is constructed. The model is applied to simulate the propagation of three historical tsunami events that attacked the east coast of Korea. The calculated free-surface displacements for the cases of the 1983 Akita and the 1993 Okushiri tsunamis are compared with the observations at four tidal stations along the east coast of Korea. The comparison shows that the results agree well with the observations. The analyses of the simulated results show that underwater topography, such as submerged rises and ridges, plays an important role in the propagation of tsunamis in this region.     

New faunal and isotopic evidence on the late Weichselian—Holocene oceanographic changes in the Norwegian Sea

Downcore studies of planktonic and benthonic foraminifera and δ¹⁸O and δ¹³C in the planktonic foraminifer Neogloboquadrina pachyderma (sin.) in two piston cores from the southern part of the Norwegian Sea suggest large changes in the oceanic circulation pattern at the end of oxygenisotope stage 2 and in the early part of stage 1. Prior to oxygen-isotope Termination IA (16,000–13,000 yr B.P.), an isolated watermass with lower oxygen content and temperature warmer than today existed below a low salinity ice-covered surface layer in the Norwegian Sea. Close to Termination IA, well-oxygenated deep water, probably with positive temperatures, was introduced. This deep water, which must have had physical and/or chemical parameters different from those of present deep water in the Norwegian Sea, could have been introduced from the North Atlantic or been formed within the basin by another mechanism than that which forms the present deep water of the Norwegian Sea. A seasonal ice cover in the southern part of the Norwegian Sea is proposed for the period between Termination IA and the beginning of IB (close to 10,000 yr B.P.). The present situation, with strong influx of warm Atlantic surface-water and deep-water formation by surface cooling, was established at Termination IB.     

Middle and late Holocene sea-levels along the Israel Mediterranean coast — evidence from ancient water wells

During the course of a study of historical water wells along the Israeli shore, which has been in progress since 1984, an innovative method for investigating sea-level fluctuations was developed. Eighteen ancient water wells were re-dug, 14 by the author, and four by archaeologists. Most of the re-dug wells are found at archaeological sites located a very short distance inland from the present shoreline. Evidence of ancient ground-water levels found in the wells directly reflects on historic eustatic sea-level changes, and the rate at which the end of the post-glacial transgression advanced. A critical question concerns the durability and life span of these wells, as the true age is very important for the accurate reconstruction of a sea-level curve. The Pre-Pottery Neolithic well of Atlit-Yam, which is the oldest known well in the world (ca. 8000 yr old), enabled the most accurate sea-level reconstruction for early Holocene times. Sea-level rise during that period of the Atlit-Yam site was of the order of 20 mm yr⁻¹ at the beginning, slowing to 6–8 mm yr⁻¹ at the abandonment of this site at ca. 7.5 ka BP, when it was flooded by the advancing and rising sea. After reaching its present level, sea-level fluctuations for the past 2.5 millennia were not greater than 1.5 to 2 m. © 1997 John Wiley & Sons, Ltd.     

Relationship between heavy metals and clay mineralogy of the modern sediment of salt marsh at the east coast of Wadden Sea, Denmark

Salt marshes play a significant roll in the marine and coast ecological systems. They can function as a sink for pollutants that would otherwise be harmful to the environment. Our investigation is mainly focused on clay mineralogy of the salt marsh sediment, metal associations in the environment of the modern （centennial） salt marsh sediment and possible relation between these metal associations and clay minerals involved. The studied salt marsh is located in the Skalingen Peninsula, West Denmark. About 85 percent of the deposited materials, including the heavy metals, was imported from the North Sea while only a small quantity of the materials was transported through the Varde River whose mouth is located about 10 km from the salt marsh, at the opposite side of the lagoon. A 25 cm high monolithic profile of the salt marsh sediment was collected and was cut into 1-cm slices. The rate of sediment accumulation, detailed grain size distribution, clay mineralogy, dating of the profile （^210Pb and ^137Cs）, content of organic matter as well as 17 metals： K, Ca, Ti, Mn, Fe, V, Cr, Co, Ni, Cu, Zn, Br, Rb, Sr, Y, Zr, Nb were investigated. Principal components and factor analyses demonstrated strong positive loadings for most of the studied metals, fine grain fractions as well as organic matter, indicating a close relation among these components. Mn, Fe, Ni, Cu, Zn, Rb were found best correlated to the clay fraction （〈2 microns）, which comprises primarily illite, kaolinite, minor chlorite and lesser smectite/illite mixed layer.     

A late Holocene record of environmental changes from the Aliki lagoon,Egion, North Peloponnesus,Greece

Aliki lagoon is a small lagoon located on the micro-tidal south coast of the Gulf of Corinth, Greece. The sediments of the lagoon recovered in three cores provide a record of late Holocene environmental change, including tectonic subsidence, tsunami layers, and change in local vegetation and sedimentation. Four periods of rapid environmental changes were identified over a 5000-yr-long record. These date from about 4700, 3000, 2500 and 2000 yr BP. Each change is linked to activity on the Egion fault, a deepening of the lagoonal bottom and a rise in relative sea level. Six tsunami events are recorded and have been caused by earthquakes on the Egion fault (three events ∼4700, ∼3000 and ∼2500 BP), Eliki fault (2350±40 yr BP) and two more distal fault ruptures. The vegetation history and pollen zones are similar to those recognised by Jahns (Vegetation Hist. Archaebot. 2 (1993) 187) on the Argive Plain, 100 km southeast of the lagoon. Five successive sedimentological configurations are established in relation to the time frame provided by the tectonic activity: (1) crevasse splay; (2) fresh to brackish water marsh; (3) and (4) brackish to hypersaline “blind” lagoon, and (5) brackish to hypersaline “blind” lagoon or brackish open lagoon.     

A comparison of evidence for late Holocene summer temperature variations in the northern hemisphere

Data on glacier, tree-line, tree-ring, pollen, and ice-core variations in North America, Greenland, and Europe during the last 2000 yr (up to A.D. 1800) are compared in detail on the century time scale. Only data that may be indicative of summer temperature changes are included, since these comprise most of the available paleoclimatic information, although some variations (especially of glaciers) may have been in response to precipitation changes instead. Radiocarbon dates and ¹⁴C-dated records are converted to calendar (dendrochronological) years using the calibration of M. Stuiver (1982, Radiocarbon 24, 1–26). Despite the basic uncertainties in dating, interpretation, response times, and “noise level” of proxy climatic data, there is at times good agreement among different kinds of evidence from within a region to suggest an episode of generally warmer or cooler summers. Three previously identified episodes find expression in records from all of the regions considered: the “Little Ice Age” of the last few centuries, a “Medieval Warm Period” around the 12th century A.D., and an earlier cold period some time between the 8th and 10th centuries. However, the timing of minima and maxima within these episodes seems to have varied from region to region (although the evidence is consistent within regions). In the 15th century, summers were warm in the eastern Canadian Arctic and southern Greenland while there was a cold episode in Europe and western North America.     

京山屈家岭地区全新世中晚期环境变化及其对人类活动的影响

通过对江汉平原北部的野外考察,结合屈家岭剖面粒度、Rb/Sr比值、磁化率和已有孢粉结果的综合分析,揭示了该地区全新世中晚期沉积环境和气候变化特征。结果表明,该剖面沉积物中粉砂(62.5～4μm)、粘粒(<4μm)约占其总量的95%以上,属于略含细砂的粘土质粉砂,概率累积曲线以三段式为主。结合地貌和岩性分析,确认该剖面以河流相沉积为主。沉积物粒度组成以粒径<30μm组分为主,同黄土的众数组分类似。也有部分样品的概率累积曲线呈现出北方黄土和下蜀黄土多见的两段式,但概率累计曲线段的斜率和中、细粒组分的相对含量都同黄土有差异。粒度组成方面同黄土沉积的某些相似特征说明,青木垱河流域广泛分布的黄土沉积可能影响了该剖面的沉积特征。沉积样品的磁化率、Rb/Sr比值和已有的孢粉分析结果反映的气候变化趋势基本上是同步的。5.2kaBP以来屈家岭遗址附近区域气候变化可以分成3个阶段:5.2～4.2kaBP期间,是较为温暖湿润的时期,水热条件好于现在,后期暖湿程度有波动性降低的趋势;4.2kaBP开始气候暖湿程度明显下降,气候转向干凉;2.0kaBP以来,本地区气候暖湿程度有所回升。该地区包括气候在内的环境变化,一定程度上影响了新石器晚期文化的演化历史。     

Palynological evidence for climatic and oceanic variability off NW Africa during the late Holocene

Pollen and organic-walled dinoflagellate cyst assemblages from core GeoB 9503-5 retrieved from the mud-belt ( 50 m water depth) off the Senegal River mouth have been analyzed to reconstruct short-term palaeoceanographic and palaeoenvironmental changes in subtropical NW Africa during the time interval from ca. 4200 to 1200 cal yr BP. Our study emphasizes significant coeval changes in continental and oceanic environments in and off Senegal and shows that initial dry conditions were followed by a strong and rapid increase in humidity between ca. 2900 and 2500 cal yr BP. After ca. 2500 cal yr BP, the environment slowly became drier again as indicated by slight increases in Sahelian savannah and desert elements in the pollen record. Around ca. 2200 cal yr BP, this relatively dry period ended with periodic pulses of high terrigenous contributions and strong fluctuations in fern spore and river plume dinoflagellate cyst percentages as well as in the fluxes of pollen, dinoflagellate cysts, fresh-water algae and plant cuticles, suggesting “episodic flash flood” events of the Senegal River. The driest phase developed after about 2100 cal yr BP.     

Holocene environmental change on the Atlantic coast of NW Iberia as inferred from the Ponzos wetland sequence

The intertidal environment of the Ponzos beach (NW Iberian Peninsula) hosts a sedimentary sequence (including large wood fragments) deposited during the first half of the Holocene in a hygrophilous continental wetland. Pollen and macrofossil data alongside radiocarbon dating allow reconstruction of the changes that occurred during the Early and Middle Holocene in the landscape of the NW Iberia coastal lowlands, as well as the local wetland plant communities, in response to the climate variations and the eustatic sea-level oscillations. The sequence represents the evolution of a coastal wetland from its initial phases as a hygrophilous wetland towards the subsequent installation of a freshwater lagoon. Pollen data show the dominant role of Atlantic (mainly deciduous) woody taxa, the scarcity of conifers and the lack of Mediterranean elements in the coastal landscapes around the Ponzos site. The presence and abundance of some taxa such as deciduous Quercus, Castanea, Fagus, Tilia and Ulmus during the Early Holocene provides further support for the occurrence of glacial refuges in the Cantabrian-Atlantic area during the Last Glaciation. The diverse vegetation that characterizes the modern landscapes in this territory established later, spreading from these glacial reservoirs of biodiversity. In this sense, the notable and early presence of Fagus at the beginning of the Holocene, a tree also previously recorded during several phases of the Last Glacial Cycle on the NW Iberia coasts, is noteworthy. In addition, during the Early and Middle Holocene are recorded other trees that are currently extirpated as natural taxa in the area, such as Pinus, Tilia and Carpinus.     

Rapid changes on the coast of Lake Peipsi and their environmental consequences

Lake Peipsi has a surface area of 3,555 km² and is the fourth largest inland body of water in Europe and one of the best-stocked for fish. Its complex geological history was controlled by the retreat of the Late Pleistocene ice, and more recently by climatic fluctuations and neotectonic movements. The northern part of the N-S elongated basin is now rising, the central part is stable, and the southern part is sinking, but in the past, the differences in elevations were much greater. These processes are still causing the water to spread from north to south, where flooding of large areas poses many social problems. Because of the considerable water-level fluctuations, exceeding 3 m, both the surface area and the volume of the lake vary greatly. High water levels cause marked shoreline damage and pose a serious threat to the buildings and roads in the immediate vicinity. Extensive changes on the coast are also due to the action of hummocky lake ice.     

Multi‐proxy evidence for early to mid‐Holocene environmental and climatic changes in northeastern Poland

Lauterbach, S., Brauer, A., Andersen, N., Danielopol, D. L., Dulski, P., Hüls, M., Milecka, K., Namiotko, T., Plessen, B., von Grafenstein, U. & DecLakes participants 2010: Multi‐proxy evidence for early to mid‐Holocene environmental and climatic changes in northeastern Poland. Boreas, 10.1111/j.1502‐3885.2010.00159.x. ISSN 0300‐9483. We investigated the sedimentary record of Lake Hańcza (northeastern Poland) using a multi‐proxy approach, focusing on early to mid‐Holocene climatic and environmental changes. AMS ¹⁴C dating of terrestrial macrofossils and sedimentation rate estimates from occasional varve thickness measurements were used to establish a chronology. The onset of the Holocene at c. 11 600 cal. a BP is marked by the decline of Lateglacial shrub vegetation and a shift from clastic‐detrital deposition to an autochthonous sedimentation dominated by biochemical calcite precipitation. Between 10 000 and 9000 cal. a BP, a further environmental and climatic improvement is indicated by the spread of deciduous forests, an increase in lake organic matter and a 1.7‰ rise in the oxygen isotope ratios of both endogenic calcite and ostracod valves. Rising δ¹⁸O values were probably caused by a combination of hydrological and climatic factors. The persistence of relatively cold and dry climate conditions in northeastern Poland during the first one and a half millennia of the Holocene could be related to a regional eastern European atmospheric circulation pattern. Prevailing anticyclonic circulation linked to a high‐pressure cell above the retreating Scandinavian Ice Sheet might have blocked the influence of warm and moist Westerlies and attenuated the early Holocene climatic amelioration in the Lake Hańcza region until the final decay of the ice sheet.     

Clay mineralogy of the late pleistocene red sediments of the Visakhapatnam region,east coast of India

The fine-fraction mineralogy of the red sediments and of the upland soils along the Visakhapatnam—Bhimunipatnam coastal region has been studied by X-ray analysis. Dominant kaolinite with subordinate illite is the general clay-mineral assemblage in both the red sediments and the soils. The similar clay-mineral composition indicates that the upland soils are the source for the clay material in the red sediments. Montmorillonite is present in some samples and shows greater abundance in the red sediments than in the soils. The additional montmorillonite is considered to have been formed by post-depositional diagenesis in the red sediments at the expense of illite. Differences in the intensity of the weathering process controlled by the gradient in the source area have been suggested as being responsible for the variation in type and abundance of the clay minerals in the red sediments. It is inferred that humid and tropical to subtropical climatic conditions prevailed and persisted throughout the Late Pleistocene and Holocene in the Visakhapatnam region.     

Palynological evidence for late Holocene environmental change on the Gimhae fluvial plain,Southern Korean peninsula: Reconstructing the rise and fall of Golden Crown Gaya State

This paper presents the results of detailed studies of palynomorphs recovered from two cores collected near the Yeanri burial mound on the Gimhae fluvial plain. Two local pollen zones were recognized on the basis of variations in the palynofloral assemblage: a lower Pollen Zone I, dominated by a Pinus‐Quercus assemblage, and an upper Pollen Zone II, dominated by a Pinus‐Quercus‐Gramineae assemblage. The palynological and molluscan analyses indicate that the depositional environments changed from a lower intertidal flat of a shallow bay environment to an upper intertidal flat in a shallow bay (before 1280 ± 110 ¹⁴C yr B.P.), and finally to a fluvial plain similar to that of today. This environmental change may have resulted from uplift along the Yangsan Fault. Afterward, the exposed area was modified by human activities, as indicated by a sudden increase in grassland herbaceous pollen grains. The loss of this bay likely had a dramatic effect on the Golden Crown Gaya State (3rd–7th centuries A.D.), which used it as a major port for regional trade, and may explain why it eventually merged with the Shilla State. © 2003 Wiley Periodicals, Inc.